Antrodia cinnamomea boosts the anti-tumor activity of sorafenib in xenograft models of human hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) has been recognized worldwide as one of the major causes of cancer death. The medicinal fungus Antrodia cinnamomea (A. cinnamomea) has been served as a functional food for liver protection. The aim of the present study was to investigate the potential activity of A. cinnamomea extracts as a safe booster for the anticancer activity of sorafenib, a multi-kinase inhibitor approved for the treatment of HCC. The biologically active triterpenoids in the ethanolic extracts of A. cinnamomea (EAC) were initially identified by HPLC/LC/MS then the different extracts and sorafenib were assessed in vitro and in vivo. EAC could effectively sensitize HCC cells to low doses of sorafenib, which was perceived via the ability of the combination to repress cell viability and to induce cell cycle arrest and apoptosis in HCC cells. The ability of EAC to enhance sorafenib activity was mediated through targeting mitogen-activated protein (MAP) kinases, modulating cyclin proteins expression and inhibiting cancer cell invasion. Moreover, the proposed combination significantly suppressed ectopic tumor growth in mice with high safety margins compared to single-agent treatment. Thus, this study highlights the advantage of combining EAC with sorafenib as a potential adjuvant therapeutic strategy against HCC.

Anti-annexin A5 antibodies and 25-hydroxy-cholecalciferol in female patients with primary antiphospholipid syndrome.

Vascular antiphospholipid syndrome (VAPS) and obstetric (OAPS) are different entities because some patients only develop thrombosis (without recurrent pregnancy losses) and vice versa. Only two articles have reported that low 25-hydroxy-cholecalciferol (vitamin D3, VD3) levels were not correlated with the presence of conventional antiphospholipid antibodies (aPL Abs: anticardiolipin (aCL), anti-beta2glycoprotein I (aß2gpI), and lupus anticoagulant (LA)), but no article analyzed the association of VD3 and anti-annexin A5 (aanxA5) Abs. The aim of our study was to investigate the association between VD3, multiple positivity of conventional aPL and aanxA5 Abs levels only in female OAPS vs. VAPS. Our study included 62 consecutive female PAPS patients. Concentrations of Abs were measured by ELISA, while VD3 levels were determined by immunochemiluminescence. Only 10/62 (16.13%) had sufficient (≥ 30 ng/ml) VD3 levels, while 48/62 (77.42%) and 4/62 (6.45%) had insufficiency and VD3 deficiency, respectively. Statistically significant VD3 deficiency was noticed in VAPS (vs. OAPS, P = 0.013). A negative correlation between VD3 levels and the age of patients was noticed (r = - 0.493, P = 0.032) only in VAPS subgroup. Multiple positivity of aPL and aanxA5 Abs was not associated with VD3 deficiency. Newly emerging aPL Abs, such as aanxA5 Abs, or their combinations with classical aPL Abs are not associated with VD3 deficiency in neither OAPS nor VAPS patients. Due to its immunomodulatory roles in B-Ly homeostasis, supplementation with VD3 should be considered in APS, at least in subgroup with severe form of the disease, i.e., VAPS.

Anti-apoptotic potential of several antidiabetic medicinal plants of the eastern James Bay Cree pharmacopeia in cultured kidney cells.

BACKGROUND: Our team has identified 17 Boreal forest species from the traditional pharmacopeia of the Eastern James Bay Cree that presented promising in vitro and in vivo biological activities in the context of type 2 diabetes (T2D). We now screened the 17 plants extracts for potential anti-apoptotic activity in cultured kidney cells and investigated the underlying mechanisms. METHODS: MDCK (Madin-Darnby Canine Kidney) cell damage was induced by hypertonic medium (700 mOsm/L) in the presence or absence of maximal nontoxic concentrations of each of the 17 plant extracts. After 18 h' treatment, cells were stained with Annexin V (AnnV) and Propidium iodide (PI) and subjected to flow cytometry to assess the cytoprotective (AnnV-/PI-) and anti-apoptotic (AnnV+/PI-) potential of the 17 plant extracts. We then selected a representative subset of species (most cytoprotective, moderately so or neutral) to measure the activity of caspases 3, 8 and 9. RESULTS: Gaultheria hispidula and Abies balsamea are amongst the most powerful cytoprotective and anti-apoptotic plants and appear to exert their modulatory effect primarily by inhibiting caspase 9 in the mitochondrial apoptotic signaling pathway. CONCLUSION: We conclude that several Cree antidiabetic plants exert anti-apoptotic activity that may be relevant in the context of diabetic nephropathy (DN) that affects a significant proportion of Cree diabetics.

Co-delivery of Se nanoparticles and pooled SiRNAs for overcoming drug resistance mediated by P-glycoprotein and class III ß-tubulin in drug-resistant breast cancers.

Drug resistance mediated by P-glycoprotein (P-gp) and class III ß-tubulin (ß-tubulin III) is a major barrier in microtubule-targeting cancer chemotherapy. In this study, layered double hydroxide nanoparticles (LDHs) were employed to simultaneously deliver selenium (Se) and pooled small interfering RNAs (siRNAs) to achieve therapeutic efficacy. LDH-supported Se nanoparticles (Se@LDH) were compacted with siRNAs (anti-P-gp and anti-ß-tubulin III) via electrostatic interactions, which could protect siRNA from degradation. Se@LDH showed excellent abilities to deliver siRNA into cells, including enhancing siRNA internalization, and promoting siRNA escape from endosomes. siRNA transfection experiments further confirmed a higher gene silencing efficiency of Se@LDH than LDH. Interestingly, we found Se@LDH may be a microtubule (MT) stabilizing agent which could inhibit cell proliferation by blocking cell cycle at G2/M phase, disrupting normal mitotic spindle formation and inducing cell apoptosis. When complexed with different specific siRNAs, Se@LDH/siRNA nanoparticles, especially the Se@LDH-pooled siRNAs, exhibit an efficient gene-silencing effect that significantly downregulate the expression of P-gp and ß-tubulin III. Moreover, Se@LDH-pooled siRNAs could induce cell apoptosis, change cell morphology and increase cellular ROS levels through change the expression of Bcl-2/Bax, activation of caspase-3, PI3K/AKT/mTOR and MAPK/ERK pathways. These results suggested that co-delivery of Se and pooled siRNAs may be a promising strategy for overcoming the drug resistance mediated by P-gp and ß-tubulin III in drug-resistant breast cancers.

Resibufogenin Induces G1-Phase Arrest through the Proteasomal Degradation of Cyclin D1 in Human Malignant Tumor Cells.

Huachansu, a traditional Chinese medicine prepared from the dried toad skin, has been used in clinical studies for various cancers in China. Resibufogenin is a component of huachansu and classified as bufadienolides. Resibufogenin has been shown to exhibit the anti-proliferative effect against cancer cells. However, the molecular mechanism of resibufogenin remains unknown. Here we report that resibufogenin induces G1-phase arrest with hypophosphorylation of retinoblastoma (RB) protein and down-regulation of cyclin D1 expression in human colon cancer HT-29 cells. Since the down-regulation of cyclin D1 was completely blocked by a proteasome inhibitor MG132, the suppression of cyclin D1 expression by resibufogenin was considered to be in a proteasome-dependent manner. It is known that glycogen synthase kinase-3ß (GSK-3ß) induces the proteasomal degradation of cyclin D1. The addition of GSK-3ß inhibitor SB216763 inhibited the reduction of cyclin D1 caused by resibufogenin. These effects on cyclin D1 by resibufogenin were also observed in human lung cancer A549 cells. These findings suggest that the anti-proliferative effect of resibufogenin may be attributed to the degradation of cyclin D1 caused by the activation of GSK-3ß.

Anticancer phototherapy using activation of E-combretastatins by two-photon-induced isomerization.

The photoisomerization of relatively nontoxic E-combretastatins to clinically active Z-isomers is shown to occur in solution through both one- and two-photon excitations at 340 and 625 nm, respectively. The photoisomerization is also demonstrated to induce mammalian cell death by a two-photon absorption process at 625 nm. Unlike conventional photodynamic therapy (PDT), the mechanism of photoisomerization is oxygen-independent and active in hypoxic environments such as in tumors. The use of red or near-infrared (NIR) light for two-photon excitation allows greater tissue penetration than conventional UV one-photon excitation. The results provide a baseline for the development of a novel phototherapy that overcomes nondiscriminative systemic toxicity of Z-combretastatins and the limitations of PDT drugs that require the presence of oxygen to promote their activity, with the added benefits of two-photon red or NIR excitation for deeper tissue penetration.

Protective effects of puerariae radix extract and its single compounds on methylglyoxal-induced apoptosis in human retinal pigment epithelial cells.

ETHNOPHARMACOLOGICAL RELEVANCE: In Korea, Puerariae radix is a medicinal plant traditionally used to treat various diseases including diabetes mellitus. To provide pharmacological basis for Puerariae radix in the treatment of diabetes, we investigated the protective effects of the ethanolic extract and its single compounds on apoptosis associated with glycation in human retinal pigment epithelial (RPE) cells. MATERIALS AND METHODS: In the present work, a quantified ethanolic extract or single compounds of Puerariae radix were selected to determine its anti-apoptotic effect in human RPE cells cultured with methylglyoxal (MG), which is a stimulator of glycation. To assess the protective effect of the extract or single compounds, the cytotoxicity assessment was performed using an MTT assay in the human RPE cells. Selected active compounds or extracts were tested by FACS analysis with annexin V staining for apoptosis. RESULTS: Daidzein (1), daidzin (2), puerarin (3), 3'-hydroxy-daidzein 8-C-apiosyl (1→6) glucoside (4), and daidzein 8-C-apiosyl (1→6) glucoside (5), and pueroside B (6) were isolated from an ethanolic extract of Puerariae radix. MG-induced apoptosis was completely inhibited by Puerariae radix, ethanolic extract, and single compounds. Of the six major compounds, daidzin (2) and 3'-hydroxy-daidzein 8-C-apiosyl (1→6) glucoside (4) significantly inhibited MG-induced apoptosis. CONCLUSION: Our results provide the first evidence that, due to its anti-glycation effect, Puerariae radix extract could inhibit MG-induced apoptosis in the cultured human RPE cells. These data suggest that Puerariae radix extract, especially its single compounds daidzin and 3'-hydroxy-daidzein 8-C-apiosyl (1→6) glucoside, has potential utility as a preventive agent for glycation-related diabetic retinopathy.

Viewing dynamic interactions of proteins and a model lipid membrane with atomic force microscopy.

The information covered in this chapter will present a model homogenous membrane preparation technique and dynamic imaging procedure that can be successfully applied to more than one type of lipid study and atomic force microscope (AFM) instrument setup. The basic procedural steps have been used with an Asylum Research MFP-3D BIO and the Bruker (formerly, Veeco) BioScope. The AFM imaging protocol has been supplemented by procedures (not to be presented in this chapter) of ellipsometry, standardized western blotting, and dot-blots to verify appropriate purity and activity of all experimental molecular components; excellent purity and activity level of the lipids, proteins, and drug(s) greatly influence the success of imaging experiments in the scanning probe microscopy field. The major goal of the chapter is to provide detailed procedures for sample preparation and operation of the Asylum Research MFP-3D BIO AFM. In addition, one should be cognizant that our comprehensive description in the use of the MFP-3D BIO's functions for successful image acquisitions and analyses is greatly enhanced by Asylum Research's (AR's) accompanying extensive manual(s), technical notes, and AR's users forum. Ultimately, the stepwise protocol and information will allow novice personnel to begin acquiring quality images for processing and analysis with minimal supervision.

The synergistic apoptotic interaction of panaxadiol and epigallocatechin gallate in human colorectal cancer cells.

Panaxadiol (PD) is a purified sapogenin of ginseng saponins, which exhibits anticancer activity. Epigallocatechin gallate (EGCG), a major catechin in green tea, is a strong botanical antioxidant. In this study, we investigated the possible synergistic anticancer effects of PD and EGCG on human colorectal cancer cells and explored the potential role of apoptosis in the synergistic activities. Effects of selected compounds on HCT-116 and SW-480 human colorectal cancer cells were evaluated by a modified trichrome stain cell proliferation analysis. Cell cycle distribution and apoptotic effects were analyzed by flow cytometry after staining with PI/RNase or annexin V/PI. Cell growth was suppressed after treatment with PD (10 and 20 µm) for 48 h. When PD (10 and 20 µm) was combined with EGCG (10, 20, and 30 µm), significantly enhanced antiproliferative effects were observed in both cell lines. Combining 20 µm of PD with 20 and 30 µm of EGCG significantly decreased S-phase fractions of cells. In the apoptotic assay, the combination of PD and EGCG significantly increased the percentage of apoptotic cells compared with PD alone (p < 0.01). The synergistic apoptotic effects were also supported by docking analysis, which demonstrated that PD and EGCG bound in two different sites of the annexin V protein. Data from this study suggested that apoptosis might play an important role in the EGCG-enhanced antiproliferative effects of PD on human colorectal cancer cells.

Antileukemic action of (-)-epicatechin in the spleen of rats with acute myeloid leukemia.

The aim of this study was to investigate whether (-)-epicatechin (EC) can induce DNA damage and apoptosis of cancer cells in the spleen of rat with acute myeloid leukemia. Healthy and leukemic rats were given EC by gavage at a dose of 40 mg/kg b.w. for 22 consecutive days. Spleen cells were subjected for analysis of DNA damage and apoptosis. The amount of DNA damage was estimated by the comet assay, while apoptosis was examined by flow cytometry using Annexin V staining. Leukemic cells were identified in the spleen cells by indirect immunofluorescence using RM-124 antibody followed by flow cytometry analysis. The results show that EC did not affect DNA damage in the splenocytes of healthy rats, but significantly increased the extent of DNA strand breaks in the spleen cells of leukemic animals. EC administration to leukemic rats induced a significant increase in the level of Annexin V-positive leukemic cells, but the level of non-leukemic Annexin V-positive cells remained unchanged in comparison to control. The percentage of leukemic cells decreased significantly under EC influence comparing to the untreated group. The results of the study reveal that EC could be used as an effective supplement of standard therapy against acute myeloid leukemia.

Identification of acupuncture-specific proteins in the process of electro-acupuncture after spinal cord injury.

Spinal cord injury (SCI) is a serious condition often affecting young and healthy individuals around the world. Electro-acupuncture (EA) has been proven to contribute towards neurologic and functional recoveries in SCI, but the underlying mechanism remains largely unknown especially regarding neural specific proteins involved in the development of EA. The protein expression profile of spinal cord in both SCI and EA treatment models was analyzed by using two-dimensional electrophoresis-based proteomics. Using a MALDI-TOF/TOF MS and subsequent protein database searching, we identified changes in 15 proteins in the spinal cord following Governor Vessel (GV) EA treatment on SCI. These proteins are involved in inflammation, cell adhesion and migration, signal transduction and apoptosis processes. We selected 2 proteins (ANXA5 and CRMP2) beneficial to neuronal survival and axonal regeneration, and further identified these protein changes using Western blot analysis. Subsequently, Nissl staining and immunofluorescence double labeling approaches were used to explore possible role of the two neural specific proteins in the process of GV-EA treatment on SCI. Our results suggest that ANXA5 and CRMP2 may be neural specific proteins in the process of GV-EA treatment on SCI. This work might contribute to the better understanding of the mechanism involved in EA treatment on SCI at protein levels and provide a new therapeutic strategy for SCI.

Entropic and enthalpic contributions to annexin V-membrane binding: a comprehensive quantitative model.

Annexin V binds to membranes with very high affinity, but the factors responsible remain to be quantitatively elucidated. Analysis by isothermal microcalorimetry and calcium titration under conditions of low membrane occupancy showed that there was a strongly positive entropy change upon binding. For vesicles containing 25% phosphatidylserine at 0.15 m ionic strength, the free energy of binding was -53 kcal/mol protein, whereas the enthalpy of binding was -38 kcal/mol. Addition of 4 m urea decreased the free energy of binding by about 30% without denaturing the protein, suggesting that hydrophobic forces make a significant contribution to binding affinity. This was confirmed by mutagenesis studies that showed that binding affinity was modulated by the hydrophobicity of surface residues that are likely to enter the interfacial region upon protein-membrane binding. The change in free energy was quantitatively consistent with predictions from the Wimley-White scale of interfacial hydrophobicity. In contrast, binding affinity was not increased by making the protein surface more positively charged, nor decreased by making it more negatively charged, ruling out general ionic interactions as major contributors to binding affinity. The affinity of annexin V was the same regardless of the head group present on the anionic phospholipids tested (phosphatidylserine, phosphatidylglycerol, phosphatidylmethanol, and cardiolipin), ruling out specific interactions between the protein and non-phosphate moieties of the head group as a significant contributor to binding affinity. Analysis by fluorescence resonance energy transfer showed that multimers did not form on phosphatidylserine membranes at low occupancy, indicating that annexin-annexin interactions did not contribute to binding affinity. In summary, binding of annexin V to membranes is driven by both enthalpic and entropic forces. Dehydration of hydrophobic regions of the protein surface as they enter the interfacial region makes an important contribution to overall binding affinity, supplementing the role of protein-calcium-phosphate chelates.

Comprehensive interaction of dicalcin with annexins in frog olfactory and respiratory cilia.

Dicalcin (renamed from p26olf) is a dimer form of S100 proteins found in frog olfactory epithelium. S100 proteins form a group of EF-hand Ca(2+)-binding proteins, and are known to interact with many kinds of target protein to modify their activities. To determine the role of dicalcin in the olfactory epithelium, we identified its binding proteins. Several proteins in frog olfactory epithelium were found to bind to dicalcin in a Ca(2+)-dependent manner. Among them, 38 kDa and 35 kDa proteins were most abundant. Our analysis showed that these were a mixture of annexin A1, annexin A2 and annexin A5. Immunohistochemical analysis showed that dicalcin and all of these three subtypes of annexin colocalize in the olfactory cilia. Dicalcin was found to be present in a quantity almost sufficient to bind all of these annexins. Colocalization of dicalcin and the three subtypes of annexin was also observed in the frog respiratory cilia. Dicalcin facilitated Ca(2+)-dependent liposome aggregation caused by annexin A1 or annexin A2, and this facilitation was additive when both annexin A1 and annexin A2 were present. In this facilitation effect, the effective Ca(2+) concentrations were different between annexin A1 and annexin A2, and therefore the dicalcin-annexin system in frog olfactory and respiratory cilia can cover a wide range of Ca(2+) concentrations. These results suggested that this system is associated with abnormal increases in the Ca(2+) concentration in the olfactory and other motile cilia.

Protective effect of green tea polyphenols on the SH-SY5Y cells against 6-OHDA induced apoptosis through ROS-NO pathway.

Green tea polyphenols (GTP) are thought to help prevent oxidative stress-related diseases, such as cancer, cardiovascular disease, neurodegenerative disease, and aging. We here investigate the protective mechanisms of GTP on SH-SY5Y cells against apoptosis induced by the pro-parkinsonian neurotoxin 6-hydroxydopamine (6-OHDA). GTP rescued the changes in condensed nuclear and apoptotic bodies, attenuated 6-OHDA-induced early apoptosis, prevented the decrease in mitochondrial membrane potential, and suppressed accumulation of reactive oxygen species (ROS) and of intracellular free Ca(2+). GTP also counteracted the 6-OHDA-induced nitric oxide increase and overexpression of nNOS and iNOS, and decreased the level of protein-bound 3-nitrotyrosine (3-NT). In addition, GTP inhibited the autooxidation of 6-OHDA and scavenged oxygen free radicals in a dose- and time-dependent manner. Our results show that the protective effects of GTP on SH-SY5Y cells are mediated, at least in part, by controlling the ROS-NO pathway.

Detection of apoptosis in cartilage in situ and in isolated chondrocytes.

Apoptosis is a form of programmed cell death conceptually opposed to necrosis. In view of the inherent difficulty in accurately detecting apoptosis in chondrocytes, this chapter describes complementary techniques that may be used in combination. During apoptotic death, protein and DNA breakdown is accomplished by caspases (cysteine proteases) in a highly regulated manner. Activation of caspases occurs in the initiation and/or the execution phase of certain apoptotic programs and represents an early physiologic marker of apoptosis. Here we present an immunoblotting technique that allows the detection of caspase-3 processing in cultured human chondrocytes. Apoptosis leads to plasma membrane asymmetry and to externalization of phosphatidylserine residues, which are bound with high affinity by annexin V. In the early stages of apoptosis, cells typically have an intact cell membrane. Apoptotic cells will not stain positive with propidium iodide, whereas externalization of phosphatidylserine will be detected by annexin V. Terminal deoxynucleotidyl transferase (TdT)-mediated nick-end labeling (TUNEL) works on the principle that DNA strand breaks (single or double) that occur during apoptosis can be identified by labeling free 3'-hydroxyl termini. Labeled nucleotides are polymerized to these termini in a reaction catalyzed by TdT. The tissue can then be examined histologically for identification of TUNEL-positive cells in situ.

Growth inhibition, cell-cycle arrest and apoptosis in human T-cell leukemia by the isothiocyanate sulforaphane.

Glucosinolates (GL) can inhibit, retard or reverse experimental multistage carcinogenesis. When brassica plant tissue is broken, GLs are hydrolyzed by the endogenous enzyme myrosinase (Myr), releasing many products including isothiocyanates (ITC). Synthetic ITCs like sulforaphane exert chemopreventive effects against chemically induced tumors in animals, modulating enzymes required for carcinogens' activation/detoxification and/or the induction of cell-cycle arrest and apoptosis in tumor cell lines. To investigate the chemopreventive potential of ITCs while reproducing the circumstances of dietary contact with sulforaphane, we studied proliferation, apoptosis induction and p53, bcl-2 and bax protein expression in Jurkat T-leukemia cells by sulforaphane, the ITC generated in situ in a quantitative manner by Myr starting from glucoraphanin (GRA). Jurkat cells were treated with different doses of GRA-Myr mixture. Effects on cell growth or survival were evaluated by counting trypan blue-excluding cells. Cell-cycle progression, apoptosis and expression of p53, bax and bcl-2 proteins were analyzed by flow cytometry. Results were analyzed by two-sided Fisher's exact test. Sulforaphane, but not GRA, caused G(2)/M-phase arrest (P = 0.028) and increase of apoptotic cell fraction (P < 0.0001) in a time- and dose-dependent manner. Necrosis was observed after prolonged exposure to elevated sulforaphane doses. Moreover, it markedly increased p53 and bax protein expression, and slightly affected bcl-2 expression. These findings indicate that sulforaphane but not the native GL GRA can exert both protective and toxic effects inhibiting leukemic cell growth. Sulforaphane therefore deserves study as a potential chemopreventive/chemotherapeutic antileukemic agent.

Incorporation of beta-selenolo[3,2-b]pyrrolyl-alanine into proteins for phase determination in protein X-ray crystallography.

beta-Selenolo[3,2-b]pyrrolyl-L-alanine that mimics tryptophan with the benzene ring of the indole moiety replaced by selenophene, was incorporated into human annexin V and barstar. This was achieved by fermentation and expression in a Trp-auxotrophic Escherichia coli host strain using the selective pressure incorporation method. The seleno- proteins were obtained in yields comparable to those of the wild-type proteins and exhibit full crystallographic isomorphism to the parent proteins, but expectedly show altered absorbance profiles and quenched tryptophan fluorescence. Since the occurrence of tryptophan residues in proteins is rare, incorporation of the electron-rich selenium-containing tryptophan surrogate into proteins represents a useful supplementation and even a promising novel alternative to selenomethionine for solving the phase problem in protein X-ray crystallography.

Domain structure and molecular conformation in annexin V/1,2-dimyristoyl-sn-glycero-3-phosphate/Ca2+ aqueous monolayers: a Brewster angle microscopy/infrared reflection-absorption spectroscopy study.

Annexins comprise a family of proteins that exhibit a Ca2+-dependent binding to phospholipid membranes that is possibly relevant to their in vivo function. Although substantial structural information about the ternary (protein/lipid/Ca2+) interaction in bulk phases has been derived from a variety of techniques, little is known about the temporal and spatial organization of ternary monolayer films. The effect of Ca2+ on the interactions between annexin V (AxV) and anionic DMPA monolayers was therefore investigated using three complementary approaches: surface pressure measurements, infrared reflection-absorption spectroscopy (IRRAS), and Brewster angle microscopy (BAM). In the absence of Ca2+, the injection of AxV into an aqueous subphase beneath a DMPA monolayer initially in a liquid expanded phase produced BAM images revealing domains of protein presumably surrounded by liquid-expanded lipid. The protein-rich areas expanded with time, resulting in reduction of the area available to the DMPA and, eventually, in the formation of condensed lipid domains in spatial regions separate from the protein film. There was thus no evidence for a specific binary AxV/lipid interaction. In contrast, injection of AxV/Ca2+ at a total Ca2+ concentration of 10 microM beneath a DMPA monolayer revealed no pure protein domains, but rather the slow formation of pinhead structures. This was followed by slow (>2 h) rigidification of the whole film accompanied by an increase in surface pressure, and connection of solid domains to form a structure resembling strings of pearls. These changes were characteristic of this specific ternary interaction. Acyl chain conformational order of the DMPA, as measured by nu(sym)CH2 near 2850 cm(-1), was increased in both the AxV/DMPA and AxV/DMPA/Ca2+ monolayers compared to either DMPA monolayers alone or in the presence of Ca2+. The utility of the combined structural and temporal information derived from these three complementary techniques for the study of monolayers in situ at the air/water interface is evident from this work.

High-level biosynthetic substitution of methionine in proteins by its analogs 2-aminohexanoic acid, selenomethionine, telluromethionine and ethionine in Escherichia coli.

We have utilized a T7 polymerase/promoter system for the high-level incorporation of methionine analogs with suitable labels for structural research (X-ray and NMR studies) on recombinant annexin V produced in Escherichia coli. Here, we describe, to our knowledge, the first biosynthetic high-level substitution of methionine by 2-aminohexanoic acid (norleucine), ethionine and telluromethionine in a protein. The replacement has been confirmed by electrospray mass spectroscopy, amino acid analysis and X-ray structural analysis. Conditions for expression were optimized concerning the frequency of appearance of revertants, high-level replacement and maximal protein yield. For the incorporation of norleucine and ethionine, E. coli B834 (DE3)(hsd metB), which is auxotrophic for methionine, was grown under methionine-limited conditions with an excess of the analog in the culture medium, and the expression of protein under the control of the T7 promoter was induced after the methionine supply had been exhausted. The factor limiting the high-level incorporation of telluromethionine into protein is its sensitivity towards oxidation. To overcome this problem, bacteria were grown with a limited amount of methionine, harvested after its exhaustion and resuspended in fresh media without methionine; telluromethionine was added and protein synthesis induced. Under these conditions, significant amounts of protein can be expressed before telluromethionine has been completely degraded (within hours). Biosynthetic incorporation of heavy atoms such as tellurium into recombinant proteins can accelerate the process of obtaining heavy-atom derivatives suitable for X-ray structural analysis, supplementing the traditional trial-and-error preparation of heavy-atom derivatives for the method of multiple isomorphous replacement. Furthermore, the successful high-level incorporation of amino acid analogs can provide single-atom mutations for the detailed study of the structure and function of proteins.