Silicon confers cucumber resistance to salinity stress through regulation of proline and cytokinins.

Salt stress is a continuous threat to global crop production. Here, we studied the alleviation role of exogenous silicon (Si) in NaCl-stressed cucumber, with special emphasis on plant growth, proline (Pro) and hormone metabolisms. The results showed that Si supplementation ameliorated the adverse effects of NaCl on plants growth, biomass, and oxidative stress. Salt stress greatly increased the content of Pro throughout the experiment, while Si regulated Pro content in two distinct ways. Si promoted the salt-induced Pro levels after 3 and 6 days of treatment, but decreased it after 9 and 12 days of treatment. Moreover, P5CS and ProDH activities and P5CS gene play important roles in Si and salt-regulated Pro levels in different stress phase. Under stress condition, Si addition tend to revert the content of ABA, IAA, cytokinin and SA to the control levels in most cases. Further correlation analysis revealed a negative correlation between the root cytokinin and Pro content after 3 days of treatment, suggesting the interaction between cytokinin and Pro metabolism. Exogenous application of Pro and ProDH competitive inhibitor D-Lactate confirmed the possible interplay between Pro and cytokinin metabolism. Further study identified several CKX (Csa4G647490 and Csa1G589070) and IPT (Csa7G392940 and Csa3G150100) genes that may be responsible for the regulation of cytokinin accumulation by Si and/or Pro after short-term of treatment. The results suggested that Pro is a key factor in Si-induced salt tolerance, and Si-increased Pro content may participate in the regulation of cytokinin metabolism under short-term of salt stress.

Effects of maternal L-proline supplementation on inflammatory cytokines at the placenta and fetus interface of mice.

Dietary L-proline (proline) supplementation during gestation enhances fetal survival and placental development in mice. The objective of the present study was to test the hypothesis that this beneficial effect of proline was associated with alterations in inflammatory response at the placenta and fetus interface. Populations of immune cells present in peripheral blood mononuclear cells (PBMC) were determined by flow cytometry analysis. The concentrations of immunoglobulins in plasma, and the concentrations of cytokines in plasma, uterus, placenta, and amniotic fluid were measured using a bead-based immunoassay. The data showed that proline supplementation led to higher (P < 0.05) populations of B lymphocytes (CD3-CD19+), natural killer (NK) cells (CD3-NK1.1+), and dendritic cells (DCs, CD11c+MHCII+) in peripheral blood, as compared with the controls. Conversely, mice fed a proline-supplemented diet had a lower population of neutrophils (CD11b+F4/80-). Further study showed that proline supplementation decreased (P < 0.05) the concentrations of (1) interleukin (IL)-23, IL-1α, and IL-6 in plasma; (2) IL-6 in the uterus; and (3) tumor necrosis factor alpha (TNF-α), monocyte chemotactic protein (MCP)-1, and IL-17 in the placenta; and (4) interferon (IFN)-γ in amniotic fluid, compared with controls. Conversely, proline supplementation resulted in higher (P < 0.05) concentrations of (1) IL-10, IL-17 and granulocyte-macrophage colony-stimulating factor (GM-CSF) in plasma; (2) IL-10 and IL-1α in the uterus; and (3) IL-1α, IL-1ß, IL-10, IL-27, and IFN-ß in amniotic fluid, compared with controls. Moreover, concentrations of immunoglobulin (Ig) G2b and IgM were enhanced (P < 0.05) by proline administration. Taken together, our results reveal a regulatory effect of proline in the immunological response at the maternal-fetal interface, which is critical for embryonic development and fetal survival.

Influence of the proline metabolism and glycine betaine on tolerance to salt stress in tomato (Solanum lycopersicum L.) commercial genotypes.

Tomato is the crop with the greatest economic importance in the world and salinity stress causes a reduction in the quantity and quality of crop production. The objective of this work is to verify if the accumulation of proline and glycine betaine (GB) and their metabolisms improve tolerance to salt stress. Two commercial genotypes of Solanum Lycopersicum L., Grand Brix and Marmande RAF were used for this work. The analyzed parameters were growth parameters, proline concentration and its metabolism, GB and its above betaine aldehyde dehydrogenase (BADH) synthesis and some related amino acids. Saline stress reduced biomass and relative growth rate (RGR) in both genotypes, this effect being greater in Marmande RAF. These results, together with the proline accumulation indicate that Grand Brix is more tolerant to saline stress. The proline increase in Grand Brix came by the ornithine pathway, leaving the glutamate pathway repressed. On the other hand, it was found in both genotypes a BADH and GB decreases as a salinity tolerance mechanism. We propose that, unlike proline, GB synthesis can produce H2O2 thereby, GB not act as compatible solute and salt tolerance does not improve.

Proline provides site-specific flexibility for in vivo collagen.

Fibrillar collagens have mechanical and biological roles, providing tissues with both tensile strength and cell binding sites which allow molecular interactions with cell-surface receptors such as integrins. A key question is: how do collagens allow tissue flexibility whilst maintaining well-defined ligand binding sites? Here we show that proline residues in collagen glycine-proline-hydroxyproline (Gly-Pro-Hyp) triplets provide local conformational flexibility, which in turn confers well-defined, low energy molecular compression-extension and bending, by employing two-dimensional 13C-13C correlation NMR spectroscopy on 13C-labelled intact ex vivo bone and in vitro osteoblast extracellular matrix. We also find that the positions of Gly-Pro-Hyp triplets are highly conserved between animal species, and are spatially clustered in the currently-accepted model of molecular ordering in collagen type I fibrils. We propose that the Gly-Pro-Hyp triplets in fibrillar collagens provide fibril "expansion joints" to maintain molecular ordering within the fibril, thereby preserving the structural integrity of ligand binding sites.

Probing the role of proline -135 on the structure, stability, and cell proliferation activity of human acidic fibroblast growth factor.

Human acidic fibroblast growth factor 1 (hFGF1) is a protein intricately involved in cell growth and tissue repair. In this study, we investigate the effect(s) of understanding the role of a conserved proline (P135), located in the heparin binding pocket, on the structure, stability, heparin binding affinity, and cell proliferation activity of hFGF1. Substitution of proline-135 with a positively charged lysine (P135K) resulted in partial destabilization of the protein; however, the overall structural integrity of the protein was maintained upon substitution of proline-135 with either a negative charge (P135E) or a polar amino acid (P135Q). Interestingly, upon heparin binding, an increase in thermal stability equivalent to that of wt-hFGF1 was observed when P135 was replaced with a positive (P135K) or a negative charge (P135E), or with a polar amino acid (P135Q). Surprisingly, introduction of negative charge in the heparin-binding pocket at position 135 (P135E) increased hFGF1's affinity for heparin by 3-fold, while the P135K mutation, did not alter the heparin-binding affinity. However, the enhanced heparin-binding affinity of mutant P135E did not translate to an increase in cell proliferation activity. Interestingly, the P135K and P135E double mutations, P135K/R136E and P135/R136E, reduced the heparin binding affinity by ∼3-fold. Furthermore, the cell proliferation activity was increased when the charge reversal mutation R136E was paired with both P135E (P135E/R136E) and P135K (P135K/R136E). Overall, the results of this study suggest that while heparin is useful for stabilizing hFGF1 on the cell surface, this interaction is not mandatory for activation of the FGF receptor.

Evaluation of proline functions in saline conditions.

More than one third of the world's irrigated lands are affected by salinity, which has great impact on plant growth and yield worldwide. Proline accumulation under salt stress has been indicated to correlate with salt tolerance. Exogenous application as well as genetic engineering of metabolic pathways involved in the metabolism of proline has been successful in improving tolerance to salinity. Correlation between proline accumulation as well as its proposed roles and salt adaptation, however, has not been clearly confirmed in several plant species. In addition, the studies relating proline functions and plant salt tolerance are always carried out in growth chambers, and are not successfully verified in field conditions. Further, plant salt tolerance is a complex trait, and studies based solely on proline accumulation do not adequately explain its functions in salinity tolerance, and thus it is difficult to interpret the discrepancies among different data. Moreover, several reports indicate that Pro role in salt tolerance is a matter of debates, as whether Pro accumulation has adaptive significance or is a consequence of alterations in cellular metabolism induced by salinity. As no consensus is obtained on the exact roles of proline production, proline exact roles in the adaptation to saline environments is therefore still lacking and is even a matter of debates. It is obvious that comprehensive future research is needed to establish the proline exact mechanism by which it enhances plant salt tolerance. We propose, however, that proline might be essential for improving salinity tolerance in some species/cultivars, but may not be relevant in others. Evidence supporting both arguments has been presented in order to reassess the feasibility of the proposed roles of Pro in plant salt tolerance mechanism.

Transcriptomic analysis comparing stay-green and senescent Sorghum bicolor lines identifies a role for proline biosynthesis in the stay-green trait.

Sorghum bicolor is an important cereal crop grown on the arid and semi-arid regions of >98 different countries. These regions are such that this crop is often subjected to low water conditions, which can compromise yields. Stay-green sorghum plants are able to retain green leaf area for longer under drought conditions and as such have higher yields than their senescent counterparts. However, the molecular and physiological basis of this drought tolerance is yet to be fully understood. Here, a transcriptomic approach was used to compare gene expression between stay-green (B35) and senescent (R16) sorghum varieties. Ontological analysis of the differentially expressed transcripts identified an enrichment of genes involved with the 'response to osmotic stress' Gene Ontology (GO) category. In particular, delta1-pyrroline-5-carboxylate synthase 2 (P5CS2) was highly expressed in the stay-green line compared with the senescent line, and this high expression was correlated with higher proline levels. Comparisons of the differentially expressed genes with those that lie in known stay-green qualitative trait loci (QTLs) revealed that P5CS2 lies within the Stg1 QTL. Polymorphisms in known cis-elements were identified in the putative promoter region of P5CS2 and these could be responsible for the differences in the expression of this gene. This study provides greater insight into the stay-green trait in sorghum. This will be greatly beneficial not only to improve our understanding of drought tolerance mechanisms in sorghum, but also to facilitate the improvement of future sorghum cultivars by marker-assisted selection (MAS).

Physiological and proteomics analyses reveal the mechanism of Eichhornia crassipes tolerance to high-concentration cadmium stress compared with Pistia stratiotes.

Cadmium (Cd) pollution is an environmental problem worldwide. Phytoremediation is a convenient method of removing Cd from both soil and water, but its efficiency is still low, especially in aquatic environments. Scientists have been trying to improve the ability of plants to absorb and accumulate Cd based on interactions between plants and Cd, especially the mechanism by which plants resist Cd. Eichhornia crassipes and Pistia stratiotes are aquatic plants commonly used in the phytoremediation of heavy metals. In the present study, we conducted physiological and biochemical analyses to compare the resistance of these two species to Cd stress at 100 mg/L. E. crassipes showed stronger resistance and was therefore used for subsequent comparative proteomics to explore the potential mechanism of E. crassipes tolerance to Cd stress at the protein level. The expression patterns of proteins in different functional categories revealed that the physiological activities and metabolic processes of E. crassipes were affected by exposure to Cd stress. However, when some proteins related to these processes were negatively inhibited, some analogous proteins were induced to compensate for the corresponding functions. As a result, E. crassipes could maintain more stable physiological parameters than P. stratiotes. Many stress-resistance substances and proteins, such as proline and heat shock proteins (HSPs) and post translational modifications, were found to be involved in the protection and repair of functional proteins. In addition, antioxidant enzymes played important roles in ROS detoxification. These findings will facilitate further understanding of the potential mechanism of plant response to Cd stress at the protein level.

Progesterone regulation of tissue factor depends on MEK1/2 activation and requires the proline-rich site on progesterone receptor.

To characterize the molecular mechanism and map the response element used by progesterone (P) to upregulate tissue factor (TF) in breast cancer cells. TF expression and mRNA levels were analyzed in breast cancer ZR-75 and T47D cells, using Western blot and real-time PCR, respectively. Mapping of the TF promoter was performed using luciferase vectors. Progesterone receptor (PR) and specificity protein 1 (Sp1) binding to the TF promoter were analyzed by chromatin immuno precipitation assay. Specific or selective inhibitors were used for the MEK1/2 and the c-Src pathways (UO126 and PP2, respectively). TF mRNA increase peaks at 18 h following P treatment in ZR-75 and T47D cells. P upregulation occurs via a transcriptional mechanism that depends on PR and MEK1/2 activation, PR and Sp1 transcription factors bind to a region in the TF promoter that contains three Sp1 sites. TF mRNA upregulation requires an intact PR proline-rich site (mPRO), but it is independent from c-Src. TF upregulation by P is mediated by Sp1 sites in the TF promoter region. Transcriptional upregulation in breast cancer cells occurs via a new mechanism that requires MEK1/2 activation and the mPRO site but independent of c-Src activity. PR Phosphorylation at serine 294 and 345 is not essential.

Validación de un método por CLAR para la cuantificación de L-prolina en la tintura al 20 por ciento de Murraya paniculata L Jack / Validation of a high performance liquid chromatography method for quantitation of L-proline in 20 percent tincture from Murraya paniculata L Jack

Introducción: la búsqueda de técnicas analíticas para el control de la calidad de los medicamentos constituye un aspecto de gran interés en el campo farmacéutico, más si van dirigidas al estudio del o los marcadores químicos de las plantas medicinales, sus extractos y fitomedicamentos. Objetivo: validar un método de cromatografía líquida de alta resolución (CLAR) para la determinación cuantitativa del aminoácido L-prolina como sustancia marcador en la tintura de Murraya paniculata L. Jack. Métodos: en el método por CLAR, la separación se realizó en una columna C-18 (UP5ODB-150/046), se utilizó como fase móvil una mezcla de solución buffer fosfato, pH ajustado a 2,4 y acetonitrilo (70:30 v/v), con una velocidad de flujo de 0,6 mL/min, modo isocrático, con detección ultravioleta a 440 nm. El volumen de inyección de la muestra fue de 20 µL. El método fue validado según la categoría I, siguiendo las exigencias internacionales. Resultados: la curva de calibración fue lineal en el rango de concentraciones ensayadas (30 a 375 µg/mL), se observó una buena precisión con coeficientes de variación menores del 2 por ciento. Los valores de recobrado estuvieron dentro de los límites establecidos para los métodos cromatográficos (98-102 por ciento). Se demostró la especificidad del método, al no presentarse interferencias de picos adicionales en la zona de elusión del compuesto de interés (L-prolina). Conclusiones: el método analítico por CLAR, validado para la cuantificación del aminoácido L-prolina en la tintura de M. paniculata, demostró ser lineal, preciso, exacto y específico bajo las condiciones de estudio(AU)

Introduction: the search for analytical methods that may monitor the quality of drugs is an issue of great interest in the pharmaceutical field, even more if they are directed to studying chemical markers of medicinal plants, their extracts and phytomedicines. Objective: to validate a high-resolution liquid chromatography (HPLC) method for the quantitative determination of the L-proline amino acid as a marker substance in Murraya paniculata L. Jack tincture. Methods: in the HPLC, the separation was performed on a C-18 (UP5ODB-150/046) column, with a mixture of phosphate buffer solution, pH adjusted to 2.4 and acetonitrile (70:30 v/v) used as mobile phase, the flow rate was 0.6 mL/min, isocratic mode with UV detection set at 440 nm. The injection volume of the sample was 20 ÁL. The method was validated according to category I, following international requirements. Results: the calibration curve was linear over the concentration range tested (30-375 mg/mL), good precision was observed with a variation coefficient less than 2 percent. Recovery values were within the limits for chromatographic methods (98-102 percent). The method was specific since there was no-interference by additional peaks in the elution zone of the compound in question (L-proline). Conclusions: the HPLC analytical method, validated for the quantification of L-proline amino acid in M. paniculata tincture, proved to be linear, precise, accurate and specific under the study conditions(AU)

Validación de un método por CLAR para la cuantificación de L-prolina en la tintura al 20 por ciento de Murraya paniculata L. Jack / Validation of a high performance liquid chromatography method for quantitation of L-proline in 20 percent tincture from Murraya paniculata L. Jack

INTRODUCCIÓN: la búsqueda de técnicas analíticas para el control de la calidad de los medicamentos constituye un aspecto de gran interés en el campo farmacéutico, más si van dirigidas al estudio del o los marcadores químicos de las plantas medicinales, sus extractos y fitomedicamentos. OBJETIVO: validar un método de cromatografía líquida de alta resolución (CLAR) para la determinación cuantitativa del aminoácido L-prolina como sustancia marcador en la tintura de Murraya paniculata L. Jack. MÉTODOS: en el método por CLAR, la separación se realizó en una columna C-18 (UP5ODB-150/046), se utilizó como fase móvil una mezcla de solución buffer fosfato, pH ajustado a 2,4 y acetonitrilo (70:30 v/v), con una velocidad de flujo de 0,6 mL/min, modo isocrático, con detección ultravioleta a 440 nm. El volumen de inyección de la muestra fue de 20 µL. El método fue validado según la categoría I, siguiendo las exigencias internacionales. RESULTADOS: la curva de calibración fue lineal en el rango de concentraciones ensayadas (30 a 375 µg/mL), se observó una buena precisión con coeficientes de variación menores del 2 por ciento. Los valores de recobrado estuvieron dentro de los límites establecidos para los métodos cromatográficos (98-102 por ciento). Se demostró la especificidad del método, al no presentarse interferencias de picos adicionales en la zona de elusión del compuesto de interés (L-prolina). CONCLUSIONES: el método analítico por CLAR, validado para la cuantificación del aminoácido L-prolina en la tintura de M. paniculata, demostró ser lineal, preciso, exacto y específico bajo las condiciones de estudio(AU)

INTRODUCTION: the search for analytical methods that may monitor the quality of drugs is an issue of great interest in the pharmaceutical field, even more if they are directed to studying chemical markers of medicinal plants, their extracts and phytomedicines. OBJECTIVE: to validate a high-resolution liquid chromatography (HPLC) method for the quantitative determination of the L-proline amino acid as a marker substance in Murraya paniculata L. Jack tincture. METHODS: in the HPLC, the separation was performed on a C-18 (UP5ODB-150/046) column, with a mixture of phosphate buffer solution, pH adjusted to 2.4 and acetonitrile (70:30 v/v) used as mobile phase, the flow rate was 0.6 mL/min, isocratic mode with UV detection set at 440 nm. The injection volume of the sample was 20 µL. The method was validated according to category I, following international requirements. RESULTS: the calibration curve was linear over the concentration range tested (30-375 mg/mL), good precision was observed with a variation coefficient less than 2 percent. Recovery values were within the limits for chromatographic methods (98-102 percent). The method was specific since there was no-interference by additional peaks in the elution zone of the compound in question (L-proline). CONCLUSIONS: the HPLC analytical method, validated for the quantification of L-proline amino acid in M. paniculata tincture, proved to be linear, precise, accurate and specific under the study conditions(AU)

Is proline accumulation per se correlated with stress tolerance or is proline homeostasis a more critical issue?

Proline has been recognized as a multi-functional molecule, accumulating in high concentrations in response to a variety of abiotic stresses. It is able to protect cells from damage by acting as both an osmotic agent and a radical scavenger. Proline accumulated during a stress episode is degraded to provide a supply of energy to drive growth once the stress is relieved. Proline homeostasis is important for actively dividing cells as it helps to maintain sustainable growth under long-term stress. It also underpins the importance of the expansion of the proline sink during the transition from vegetative to reproductive growth and the initiation of seed development. Its role in the reproductive tissue is to stabilize seed set and productivity. Thus, to cope with abiotic stress, it is important to develop strategies to increase the proline sink in the reproductive tissue. We give a holistic account of proline homeostasis, taking into account the regulation of proline synthesis, its catabolism, and intra- and intercellular transport, all of which are vital components of growth and development in plants challenged by stress.

Flight muscle-specific Pro-Ala-rich extension of troponin is important for maintaining the insect-type myofilament lattice integrity.

Insect flight muscle (IFM) can oscillate at frequencies up to 1000Hz, owing to its capability of stretch activation (SA). It is a highly specialized form of cross striated muscles, and its peculiar features include the IFM-specific isoform of troponin-I (troponin-H or TnH) with an unusually long Pro-Ala-rich extension at the C-terminus. Although we have shown that this extension does not directly take part in SA, questions remain as to what its real role is and why it is expressed only in IFM. Here we explored the structural role of the extension, be comparing X-ray diffraction patterns and electron micrographs of bumblebee IFM fibers before and after enzymatic removal of the extension. The removal had a dramatic effect on diffraction patterns: In IFMs in general, the equatorial 2,0 reflection is much stronger than the 1,1 reflection, but after removal, their intensities became almost equal (stronger 1,1 is a feature of vertebrate skeletal muscle). Electron micrographs revealed that a substantial fraction of the thin filaments showed a tendency to move towards the vertebrate position (the trigonal position between three thick filaments), while the rest of the thin filaments remained in their original insect position (midway between two neighboring thick filaments). Therefore, one of the roles of the extension is suggested to keep the filament lattice in the correct configuration for IFM. This insect-type lattice structure is preserved among IFMs from varied insect orders but not in body muscles, suggesting that the maintenance of this lattice structure is important for flight functions.

Activation of p53 following ionizing radiation, but not other stressors, is dependent on the proline-rich domain (PRD).

The tumor suppressor protein, p53 is one of the most important cellular defences against malignant transformation. In response to cellular stressors p53 can induce apoptosis, cell cycle arrest or senescence as well as aid in DNA repair. Which p53 function is required for tumor suppression is unclear. The proline-rich domain (PRD) of p53 (residues 58-101) has been reported to be essential for the induction of apoptosis. To determine the importance of the PRD in tumor suppression in vivo we previously generated a mouse containing a 33-amino-acid deletion (residues 55-88) in p53 (mΔpro). We showed that mΔpro mice are protected from T-cell tumors but not late-onset B-cell tumors. Here, we characterize the functionality of the PRD and show that it is important for mediating the p53 response to DNA damage induced by γ-radiation, but not the p53-mediated responses to Ha-Ras expression or oxidative stress. We conclude that the PRD is important for receiving incoming activating signals. Failure of PRD mutants to respond to the activating signaling produced by DNA damage leads to impaired downstream signaling, accumulation of mutations, which potentially leads to late-onset tumors.

[Proline, a multifunctional amino-acid involved in plant adaptation to environmental constraints]. / La proline, un acide aminé multifonctionnel impliqué dans l'adaptation des plantes aux contraintes environnementales.

In addition to its role in primary metabolism as a component of proteins, proline is one of the most widely distributed compatible solutes that accumulates in plants during adverse environmental constraints and plays an important role in plant stress tolerance. Proline was proposed to act as stabilizer for proteins and macromolecular complexes, scavenger of free radicals and regulator of cellular redox potential. Intracellular proline concentration depends on a tight regulation between its biosynthesis and catabolism. However the exact role of proline and the signaling pathways involved in the regulation of its metabolism are not completely known yet. Investigation of proline metabolism in model plants would allow to acquire information about the diversity of the mechanisms developed by plants to overcome environmental constraints and to establish some reliable tools for the improvement of crop tolerance.

The TßR-I pre-helix extension is structurally ordered in the unbound form and its flanking prolines are essential for binding.

Transforming growth factor ß isoforms (TGF-ß) are among the most recently evolved members of a signaling superfamily with more than 30 members. TGF-ß play vital roles in regulating cellular growth and differentiation, and they signal through a highly restricted subset of receptors known as TGF-ß type I receptor (TßR-I) and TGF-ß type II receptor (TßR-II). TGF-ß's specificity for TßR-I has been proposed to arise from its pre-helix extension, a five-residue loop that binds in the cleft between TGF-ß and TßR-II. The structure and backbone dynamics of the unbound form of the TßR-I extracellular domain were determined using NMR to investigate the extension's role in binding. This showed that the unbound form is highly similar to the bound form in terms of both the ß-strand framework that defines the three-finger toxin fold and the extension and its characteristic cis-Ile54-Pro55 peptide bond. The NMR data further showed that the extension and two flanking 3(10) helices are rigid on the nanosecond-to-picosecond timescale. The functional significance of several residues within the extension was investigated by binding studies and reporter gene assays in cultured epithelial cells. These demonstrated that the pre-helix extension is essential for binding, with Pro55 and Pro59 each playing a major role. These findings suggest that the pre-helix extension and its flanking prolines evolved to endow the TGF-ß signaling complex with its unique specificity, departing from the ancestral promiscuity of the bone morphogenetic protein subfamily, where the binding interface of the type I receptor is highly flexible.

Prolines in ßA-sheet of neural cadherin act as a switch to control the dynamics of the equilibrium between monomer and dimer.

Neural cadherins dimerize through the formation of calcium-dependent strand-crossover structures. Dimerization of cadherins leads to cell-cell adhesion in multicellular organisms. Strand-crossover dimer forms exclusively between the first N-terminal extracellular modules (EC1) of the adhesive partners via swapping of their ßA-sheets and docking of tryptophan-2 in the hydrophobic pocket. In the apo-state wild-type cadherin is predominantly monomer, which indicates that the dimerization is energetically unfavorable in the absence of calcium. Addition of calcium favors dimer formation by creating strain in the monomer and lowering the energetic barrier between monomer and dimer. Dynamics of the monomer-dimer equilibrium is vital for plasticity of synapses. Prolines recurrently occur in proteins that form strand-crossover dimer and are believed to be the source of the strain in the monomer. N-cadherins have two proline residues in the ßA-sheet. We focused our studies on the role of these two prolines in calcium-dependent dimerization. Spectroscopic, electrophoretic, and chromatopgraphic studies showed that mutations of both prolines to alanines increased the dimerization affinity by ~20-fold and relieved the requirement of calcium in dimerization. The P5A and P6A mutant formed very stable dimers that required denaturation of protein to disassemble in the apo conditions. In summary, the proline residues act as a switch to control the dynamics of the equilibrium between monomer and dimer which is crucial for the plasticity of synapses.

A self-propagating matrix metalloprotease-9 (MMP-9) dependent cycle of chronic neutrophilic inflammation.

BACKGROUND: Chronic neutrophilic inflammation is a poorly understood feature in a variety of diseases with notable worldwide morbidity and mortality. We have recently characterized N-acetyl Pro-Gly-Pro (Ac-PGP) as an important neutrophil (PMN) chemoattractant in chronic inflammation generated from the breakdown of collagen by the actions of MMP-9. MMP-9 is present in the granules of PMNs and is differentially released during inflammation but whether Ac-PGP contributes to this ongoing proteolytic activity in chronic neutrophilic inflammation is currently unknown. METHODOLOGY/PRINCIPAL FINDINGS: Utilizing isolated primary blood PMNs from human donors, we found that Ac-PGP induces significant release of MMP-9 and concurrently activates the ERK1/2 MAPK pathway. This MMP-9 release is attenuated by an inhibitor of ERK1/2 MAPK and upstream blockade of CXCR1 and CXCR2 receptors with repertaxin leads to decreased MMP-9 release and ERK 1/2 MAPK activation. Supernatants obtained from PMNs stimulated by Ac-PGP generate more Ac-PGP when incubated with intact collagen ex vivo; this effect is inhibited by an ERK1/2 pathway inhibitor. Finally, clinical samples from individuals with CF demonstrate a notable correlation between Ac-PGP (as measured by liquid chromatography-tandem mass spectrometry) and MMP-9 levels even when accounting for total PMN burden. CONCLUSIONS/SIGNIFICANCE: These data indicate that ECM-derived Ac-PGP could result in a feed-forward cycle by releasing MMP-9 from activated PMNs through the ligation of CXCR1 and CXCR2 and subsequent activation of the ERK1/2 MAPK, highlighting for the first time a matrix-derived chemokine (matrikine) augmenting its generation through a discrete receptor/intracellular signaling pathway. These findings have notable implications to the development unrelenting chronic PMN inflammation in human disease.

Proline 96 of the copper ligand loop of amicyanin regulates electron transfer from methylamine dehydrogenase by positioning other residues at the protein-protein interface.

Amicyanin is a type 1 copper protein that serves as an electron acceptor for methylamine dehydrogenase (MADH). The site of interaction with MADH is a "hydrophobic patch" of amino acid residues including those that comprise a "ligand loop" that provides three of the four copper ligands. Three prolines are present in this region. Pro94 of the ligand loop was previously shown to strongly influence the redox potential of amicyanin but not affinity for MADH or mechanism of electron transfer (ET). In this study Pro96 of the ligand loop was mutated. P96A and P96G mutations did not affect the spectroscopic or redox properties of amicyanin but increased the K(d) for complex formation with MADH and altered the kinetic mechanism for the interprotein ET reaction. Values of reorganization energy (λ) and electronic coupling (H(AB)) for the ET reaction with MADH were both increased by the mutation, indicating that the true ET reaction observed with native amicyanin was now gated by or coupled to a reconfiguration of the proteins within the complex. The crystal structure of P96G amicyanin was very similar to that of native amicyanin, but notably, in addition to the change in Pro96, the side chains of residues Phe97 and Arg99 were oriented differently. These two residues were previously shown to make contacts with MADH that were important for stabilizing the amicyanin-MADH complex. The values of K(d), λ, and H(AB) for the reactions of the Pro96 mutants with MADH are remarkably similar to those obtained previously for P52G amicyanin. Mutation of this proline, also in the hydrophobic patch, caused reorientation of the side chain of Met51, another reside that interacted with MADH and caused a change in the kinetic mechanism of ET from MADH. These results show that proline residues near the copper site play key roles in positioning other amino acid residues at the amicyanin-MADH interface not only for specific binding to the redox protein partner but also to optimize the orientation of proteins for interprotein ET.

Effect of glyprolines PGP, GP, and PG on homeostasis of gastric mucosa in rats with experimental ethanol-induced gastric ulcers.

The decrease in the severity of erosions and ulcer lesions after preventive treatment with PGP or PG correlated with a decrease in the content of lipid peroxidation products to a control level. Activities of SOD and catalase also returned to control values. GP produced the weakest effect on pro- and antioxidant state of the gastric mucosa. We concluded that the pronounced preventive effect of PGP and PG on the development of ethanol-induced erosions and ulcer lesions is largely determined by their antioxidant properties. Glyprolines can be considered as a promising means for prevention and treatment of stomach and duodenal ulcers.