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1.
Mol Biol Rep ; 48(6): 5135-5142, 2021 Jun.
Article in English | MEDLINE | ID: mdl-34231097

ABSTRACT

Actin-binding proteins (ABPs) and various signaling systems are involved in the process of squamous cell carcinoma of the larynx and hypopharynx (SCCLH) metastasis. The clinical significance of these proteins has not yet been determined. We analyzed the relationship between the mRNA levels of cofilin 1 (CFL1), profilin 1 (PFN1), adenylyl cyclase-associated protein 1 (CAP1), SNAI1 and RND3 and SCCLH metastasis. The serum levels of the above ABPs were estimated and the relationship between them and their mRNA expressions was analyzed. The expression levels of ABP mRNAs were measured by real-time RT-PCR in paired tissue samples taken from 54 patients with SCCLH (T1-4N0-1M0). Expression analysis was performed using the 2-ΔΔCT method. The levels of ABPs in the blood serum were measured by ELISA. Statistical analysis was carried out using the SPSS Statistica 20.0 software package. No significant difference in the mRNA gene expression in tumor tissue of patients with T1-3N0M0 SCCLH and patients with T2-4N1-2M0 SCCLH was found. High expression of RND3 mRNA was accompanied by an increase in mRNA expression of all studied ABPs. In the blood serum of T2-4N1-2M0 patients, the level of PFN1 was lower by 21% and the level of CAP1 was higher by 75% than those observed in T1-4N0M0 patients. The data obtained showed that RND3 is involved in the regulation of molecular cascades of SCCLH metastasis. PFN1 and CAP1 serum levels can be good classifiers of metastases in patients with SCCLH.


Subject(s)
Hypopharyngeal Neoplasms/metabolism , Laryngeal Neoplasms/metabolism , Microfilament Proteins/genetics , Adult , Aged , Carcinoma, Squamous Cell/pathology , Cell Cycle Proteins/analysis , Cell Cycle Proteins/blood , Cell Cycle Proteins/genetics , Cofilin 1/analysis , Cofilin 1/blood , Cofilin 1/genetics , Cytoskeletal Proteins/analysis , Cytoskeletal Proteins/blood , Cytoskeletal Proteins/genetics , Cytoskeleton/metabolism , Female , Head and Neck Neoplasms/pathology , Humans , Hypopharyngeal Neoplasms/blood , Hypopharyngeal Neoplasms/genetics , Laryngeal Neoplasms/blood , Male , Microfilament Proteins/metabolism , Middle Aged , Profilins/analysis , Profilins/blood , Profilins/genetics , RNA, Messenger/genetics , Russia , Serum/metabolism , Signal Transduction/genetics , Snail Family Transcription Factors/genetics , Squamous Cell Carcinoma of Head and Neck/genetics , Squamous Cell Carcinoma of Head and Neck/metabolism , Squamous Cell Carcinoma of Head and Neck/pathology , rho GTP-Binding Proteins/genetics
2.
Int J Med Sci ; 17(17): 2850-2860, 2020.
Article in English | MEDLINE | ID: mdl-33162813

ABSTRACT

Renal fibrosis is one of the main causes of chronic kidney disease. Many studies have focused on fibroblasts and myofibroblasts involved in renal fibrogenesis. Recently, several studies have reported that renal proximal tubule epithelial cells are possible initiators of renal fibrosis. However, the mechanism through which cells induce renal fibrosis is poorly understood. In this study, we found that CK2α induces fibrosis in renal proximal tubule epithelial cells (TH1) by regulating the expression of profilin-1 (Pfn1). CKD mouse model and TH1 cells treated with P-cresol also showed an increased level of Pfn1. The knockdown of CK2α suppressed fibrosis in TH1 cells via the downregulation of Pfn1. In particular, CK2α knockdown inhibited the expression of stress fibers and fibrosis-related proteins in P-cresol-treated TH1 cells. Furthermore, the knockdown of CK2α inhibited mitochondrial dysfunction and restored cellular senescence and cell cycle in P-cresol-treated TH1 cells. These results indicate that CK2α induces renal fibrosis through Pfn1, which makes CK2α a key target molecule in the treatment of fibrosis related to chronic kidney disease.


Subject(s)
Kidney Tubules, Proximal/pathology , Profilins/metabolism , Renal Insufficiency, Chronic/pathology , Adenine/administration & dosage , Adenine/toxicity , Animals , Casein Kinase II/genetics , Casein Kinase II/metabolism , Cell Line , Cellular Senescence , Cresols/toxicity , Disease Models, Animal , Epithelial Cells , Fibrosis , Gene Knockdown Techniques , Humans , Kidney Tubules, Proximal/drug effects , Male , Profilins/blood , Profilins/genetics , Renal Insufficiency, Chronic/blood , Renal Insufficiency, Chronic/chemically induced
3.
Eur Rev Med Pharmacol Sci ; 24(15): 8112-8116, 2020 08.
Article in English | MEDLINE | ID: mdl-32767339

ABSTRACT

OBJECTIVE: Profilin 1 (Pfn1) is likely to be involved in atherogenesis and myocardial infarction (MI). Clinical data on this subject are very limited. The aim of this study was to search for associations between serum Pfn1 and a number of parameters in MI patients: symptom onset to PCI time (OPT), myocardial necrosis markers, thrombolysis in myocardial infarction (TIMI) flow, antiplatelet drugs, heparin administration and typical atherosclerosis risk factors. PATIENTS AND METHODS: We included patients with type 1 MI (according to the Third Universal Definition of Myocardial Infarction) who were able to precisely determine the time of symptom onset. Exclusion criteria involved conditions potentially altering platelet function. We screened 114 patients and included 65. We assessed serum Pfn1 in three time points: on admission (Pfn1_0), 24 hours post PCI (Pfn1_24) and 48 hours post PCI (Pfn1_48) and correlated it with OPT, cardiac necrosis markers (troponin T, CK, CKMB), TIMI flow in the infarct-related artery, pre-hospital P2Y12-antagonist and heparin administration and known atherosclerosis risk factors. RESULTS: Patients with a shorter OPT had higher Pfn1_0 (838.5 vs. 687.1 pg/ml, p=0.007). Patients with impaired coronary flow post PCI had lower Pfn1_24 (748.2 vs. 925.2 pg/ml, p=0.017) and Pfn1_48 (744.5 vs. 879.8, p=0.031. Pfn1_24 and Pfn1_48 were lower in patients who received a P2Y12 antagonist prior to hospital admission. Diabetic patients presented with lower Pfn1_0 concentrations. CONCLUSIONS: This is the first study assessing Pfn1 in type 1 MI patients in relation to the chosen parameters. Pfn1 may be a biochemical tool to objectify information on OPT in MI patients. We found an association between Pfn1 and post-PCI TIMI flow, antiplatelet drug administration and diabetes mellitus.


Subject(s)
Myocardial Infarction/blood , Profilins/blood , Biomarkers/blood , Humans
4.
Allergy ; 75(4): 853-861, 2020 04.
Article in English | MEDLINE | ID: mdl-31804710

ABSTRACT

BACKGROUND: The capacity of profilin to induce allergic symptoms in patients with respiratory allergy has been questioned. In this sense, the aim of this study was to investigate the correlation between profilin exposure and induction of symptoms in a prospective case-control study. METHODS: The concentration of profilin as well as pollen levels in the air was measured. A diary score of symptoms was collected from allergic patients. Seventy-nine individuals were included in the study; fifty cases and 28 controls were positive or negative to profilin, respectively. Conjunctival and bronchial provocation tests were performed with purified profilin (Pho d 2) in a subgroup of cases and controls. RESULTS: Profilin was detected in the environment on 133 days (maximum peak of 0.56 ng/m3 ). A positive correlation between profilin and pollen count of Olea and Poaceae was observed (ρ = 0.24; P < .001). Intensity of total, nasal and ocular symptoms was statistically higher in cases than in controls (P < .001). The risk of suffering symptoms, measured by the percentage of patients who presented any of the symptoms each day, was also higher in cases than in controls. The provocation test was positive in 95% of bronchial and 90% of conjunctival challenges in cases, and negative in all controls. CONCLUSIONS: Profilin was detected in the environment and had the ability to induce a specific allergen response. Patients sensitized to this panallergen showed more symptoms and were more likely to have symptoms. Therefore, sensitization to profilin seems to be a marker of severity in patients with rhinoconjunctivitis and asthma mediated by pollen.


Subject(s)
Allergens , Hypersensitivity , Pollen , Profilins , Case-Control Studies , Humans , Hypersensitivity/blood , Pollen/immunology , Profilins/blood , Prospective Studies
5.
Medicina (Kaunas) ; 55(5)2019 May 21.
Article in English | MEDLINE | ID: mdl-31117233

ABSTRACT

BACKGROUND AND OBJECTIVES: Nearly 20-30% of the world's population suffers from allergic rhinitis, among them 15% are progressing to asthma conditions. Sorghum bicolor profilin (Sorb PF), one of the panallergens, was identified, but the allergen specificity is not yet characterized. MATERIALS AND METHODS: To map the antigenic determinants responsible for IgE binding, the present study is focused on in silico modeling, simulation of Sorb PF and docking of the Sorb PF peptides (PF1-6) against IgG and IgE, followed by in vivo evaluation of the peptides for its allergenicity in mice. RESULTS: Peptide PF3 and PF4 displayed high docking G-scores (-9.05) against IgE only. The mice sensitized with PF3 peptide showed increased levels of IL5, IL12, TNF-alpha, and GMCSF when compared to other peptides and controls, signifying a strong, Th2-based response. Concurrently, the Th1 pathway was inhibited by low levels of cytokine IL2, IFN-γ, and IL-10 justifying the role of PF3 in allergenic IgE response. CONCLUSIONS: Based on the results of overlapping peptides PF3 and PF4, the N-terminal part of the PF3 peptide (TGQALVI) plays a crucial role in allergenic response of Sorghum profilin.


Subject(s)
Computer Simulation , Peptide Mapping/methods , Profilins/analysis , Sorghum/adverse effects , Animals , Disease Models, Animal , Epitopes/analysis , Mice , Profilins/blood , Sorghum/cytology
6.
J Mass Spectrom ; 53(12): 1189-1197, 2018 Dec.
Article in English | MEDLINE | ID: mdl-30251292

ABSTRACT

In the hospital, blood samples are collected to monitor patients' health states, and thus various protein-based clinical methods have been developed. However, some proteins are found to change in abundances during the process of blood collection and storage. In order to account such pre-analytical effects, we performed liquid chromatography multiple reaction monitoring mass spectrometry (LC-MRM-MS) on 15 selected proteins in plasma samples prepared by varying storage time and temperature of whole blood prior to plasma isolation. Two cytosolic proteins, profilin-1 (PFN1) and thymosin beta-4 (TMSB4X), were absolutely quantified using 15 N-labeled recombinant proteins spiked externally. The other 13 proteins were quantified in a relative way compared with the two reference proteins. Triplicated LC-MRM-MS measurements showed that the median CV of MRM peak areas was 5.7%. The amounts of PFN1 and TMSB4X increased rapidly depending on the storage time between blood collection and plasma preparation. It indicates the leakage of cellular components into the plasma fraction. Relative quantification further revealed that five proteins including PFN1, S10A8, S10A9, S10A11, and TMSB4X showed significant difference (P < 0.05). We further monitored PFN1 and TMSB4X on 40 samples collected for protein diagnostics under a typical clinical study condition. Compared with the plasma samples prepared within a day, the level of both PFN1 and TMSB4X increased in the plasma samples prepared from the blood collected the day before and kept overnight at 4°C (0.51 to 3.11 µg/mL for PFN1 and 0.98 to 5.36 µg/mL for TMSB4X in average). Our result suggests an effort of assuring plasma quality for accurate protein-based diagnosis or biomarker discovery and validation.


Subject(s)
Profilins/blood , Tandem Mass Spectrometry/methods , Thymosin/blood , Biomarkers/blood , Blood Preservation , Chromatography, High Pressure Liquid , Humans , Isotope Labeling , Nitrogen Isotopes , Plasma , Recombinant Proteins/blood , Time Factors
7.
Eur J Clin Invest ; 47(12)2017 Dec.
Article in English | MEDLINE | ID: mdl-28981140

ABSTRACT

BACKGROUND: Profilin-1 is a ubiquitous, actin-binding protein that plays an important role in the regulation of actin polymerization and cytoskeleton remodelling and contributes to vascular dysfunction. We conducted this study to investigate the association of serum profilin-1 levels with fatal and nonfatal CVE in a cohort of patients with stage 1-5 CKD. MATERIALS AND METHODS: Serum concentrations of profilin-1 levels were determined by enzyme-linked immunosorbent assay. Endothelium-dependent vasodilatation (flow-mediated dilatation [FMD]) and endothelium-independent vasodilatation (nitroglycerine-mediated dilatation [NMD]) of the brachial artery were assessed noninvasively, using high-resolution ultrasound. RESULTS: Both fatal and nonfatal CVE were significantly higher in patients with high profilin-1 levels. Kaplan-Meier survival curves showed that patients with profilin-1 below the median value (114 pg/mL) had higher cumulative survival compared with patients who had profilin-1 levels above the median value (log-rank test, P < .001). CONCLUSIONS: This is the first study that demonstrates the serum profilin-1 is independently associated with endothelial dysfunction, cardiovascular events and survival in patients with CKD.


Subject(s)
Cardiovascular Diseases/blood , Profilins/blood , Renal Insufficiency, Chronic/blood , Adult , Brachial Artery/diagnostic imaging , Brachial Artery/physiopathology , Cardiovascular Diseases/mortality , Cardiovascular Diseases/physiopathology , Cause of Death , Female , Humans , Kaplan-Meier Estimate , Male , Middle Aged , Mortality , Prognosis , Renal Insufficiency, Chronic/physiopathology , Ultrasonography , Vasodilation/physiology
8.
Am J Hypertens ; 30(10): 1024-1031, 2017 Oct 01.
Article in English | MEDLINE | ID: mdl-28541412

ABSTRACT

BACKGROUND: Animal researches reported that the dysfunction of profilin1 (PFN1) was involved in the physiological arterial stiffness and vascular remodeling linking to the etiology of hypertension (HT). This study mainly aims at evaluating the association of PFN1 and HT in a Han Chinese population. METHODS: A case-control study consisted of 2,012 HT cases and 2,210 controls was conducted and 2,116 participants from the healthy controls were further followed up for average 5.01 years. Logistic and Cox regression models were applied to evaluate the association of 4 tag single nucleotide polymorphisms (SNPs) of PFN1 and ENO3 with HT. RESULTS: There was no significant association of the 4 SNPs between HT cases and controls even after adjustment for confounding factors (P > 0.05). Haplotype analysis did not identify any significant haplotype with HT. There were no statistical difference of systolic blood pressure (BP) and diastolic BP among different genotypes in antihypertensive-treated group and untreated group. In follow-up population, there was no significant association of candidate SNPs with HT even after adjustment for covariates (all P > 0.05). Of note, the plasma profilin1 level of HT cases was significantly higher than that of control subjects (P = 0.011). The profilin1 levels of controls significantly decreased with variation of rs238243 at PFN1 (P = 0.041), and the profilin1 levels of HT cases increased with variation of rs238238 at ENO3 (P = 0.004). CONCLUSIONS: Our results suggest that HT cases displayed an elevated plasma profilin1. Variants of rs238243 and rs238238 might regulate profilin1 expression by epigenetic modification and indirectly affects the susceptible threshold of HT.


Subject(s)
Blood Pressure/genetics , Hypertension/genetics , Polymorphism, Single Nucleotide , Profilins/genetics , Aged , Antihypertensive Agents/therapeutic use , Asian People/genetics , Blood Pressure/drug effects , Case-Control Studies , Chi-Square Distribution , China , Female , Follow-Up Studies , Genetic Association Studies , Genetic Predisposition to Disease , Haplotypes , Humans , Hypertension/diagnosis , Hypertension/ethnology , Hypertension/physiopathology , Incidence , Linear Models , Logistic Models , Male , Middle Aged , Odds Ratio , Phenotype , Phosphopyruvate Hydratase/genetics , Profilins/blood , Proportional Hazards Models , Risk Factors
9.
Article in English | MEDLINE | ID: mdl-27164624

ABSTRACT

BACKGROUND: Multiple sensitization is frequent among pollen-allergic patients. The goal of this study was to determine the diagnostic accuracy of the ImmunoCAP ISAC 112 (ISAC112) microarray in allergy to pollen from several taxa and its clinical utility in a Spanish population. METHODS: Specific IgE was determined in 390 pollen-allergic patients using the ISAC112 microarray. Diagnostic accuracy (sensitivity, specificity, predictive values, and area under the ROC curve) was calculated for the diagnosis of allergy to pollen from grass (n=49), cypress (n=75), olive tree (n=33), plane tree (n=63), and pellitory of the wall (n=17) and compared with that of the singleplex ImmunoCAP immunoassay. RESULTS: The sensitivity of the ISAC112 microarray ranged from 68.2% for allergy to plane tree pollen to 93.9% for allergy to grass pollen. The specificity was >90%. The AUC for the diagnosis of allergy to plane tree pollen was 0.798, whereas the AUC for the remaining cases was ≥0.876. The accuracy of ISAC112 was higher than that of ImmunoCAP for plane tree pollen and similar for the remaining pollens. The frequency of sensitization to most species-specific allergenic components and profilins varied between the different geographical regions studied. A total of 73% of pollen-allergic patients were sensitized to species-specific components of more than 1 pollen type. CONCLUSIONS: The ISAC112 microarray is an accurate tool for the diagnosis of allergy to pollen from grass, cypress, olive tree, plane tree, and pellitory of the wall. The features of the ISAC112 microarray are similar or superior (in the case of plane tree pollen) to those of ImmunoCAP. This microarray is particularly useful for the etiologic diagnosis of pollinosis in patients sensitized to multiple pollen species whose pollination periods overlap.


Subject(s)
Allergens/immunology , Immunoglobulin E/blood , Microarray Analysis/statistics & numerical data , Pollen/immunology , Respiratory Hypersensitivity/diagnosis , Respiratory Hypersensitivity/immunology , Adult , Allergens/classification , Area Under Curve , Female , Gene Expression , Humans , Male , Middle Aged , Poaceae/immunology , Pollen/classification , Predictive Value of Tests , Profilins/blood , Profilins/genetics , ROC Curve , Respiratory Hypersensitivity/blood , Respiratory Hypersensitivity/pathology , Spain , Species Specificity , Trees/immunology
10.
Article in English | MEDLINE | ID: mdl-27105922

ABSTRACT

OBJECTIVE: Major depressive disorder (MDD) is a systemic and multifactorial disorder involving complex interactions between genetic predisposition and disturbances of various molecular pathways. Its underlying molecular pathophysiology remains unclear, and no valid and objective diagnostic tools for the condition are available. METHODS: We performed large-scale proteomic profiling to identify novel peripheral biomarkers implicated in the pathophysiology of MDD in 25 drug-free female MDD patients and 25 healthy controls. First, quantitative serum proteome profiles were obtained and analyzed by liquid chromatography-tandem mass spectrometry using serum samples from 10 MDD patients and 10 healthy controls. Next, candidate biomarker sets, including differentially expressed proteins from the profiling experiment and those identified in the literature, were verified using multiple-reaction monitoring in 25 patients and 25 healthy controls. The final panel of potential biomarkers was selected using multiparametric statistical analysis. RESULTS: We identified a serum biomarker panel consisting of six proteins: apolipoprotein D, apolipoprotein B, vitamin D-binding protein, ceruloplasmin, hornerin, and profilin 1, which could be used to distinguish MDD patients from controls with 68% diagnostic accuracy. Our results suggest that modulation of the immune and inflammatory systems and lipid metabolism are involved in the pathophysiology of MDD. CONCLUSIONS: Our findings of functional proteomic changes in the peripheral blood of patients with MDD further clarify the molecular biological pathway underlying depression. Further studies using larger, independent cohorts are needed to verify the role of these candidate biomarkers for the diagnosis of MDD.


Subject(s)
Depressive Disorder, Major/blood , Adult , Apolipoprotein B-100/blood , Apolipoproteins D/blood , Biomarkers/blood , Blood Chemical Analysis , Calcium-Binding Proteins/blood , Ceruloplasmin/metabolism , Chromatography, High Pressure Liquid , Cohort Studies , Female , Gene Expression Profiling , Humans , Intermediate Filament Proteins/blood , Profilins/blood , Proteome , Psychiatric Status Rating Scales , Tandem Mass Spectrometry , Vitamin D-Binding Protein/blood
12.
Vet Parasitol ; 181(2-4): 97-105, 2011 Sep 27.
Article in English | MEDLINE | ID: mdl-21676547

ABSTRACT

Two phytonutrient mixtures, VAC (carvacrol, cinnamaldehyde, and Capsicum oleoresin), and MC (Capsicum oleoresin and turmeric oleoresin), were evaluated for their effects on chicken immune responses following immunization with an Eimeria profilin protein. Chickens were fed with a non-supplemented diet, or with VAC- or MC-supplemented diets, immunized with profilin, and orally challenged with virulent oocysts of Eimeria tenella. Immunity against infection was evaluated by body weight, fecal oocyst shedding, profilin antibody levels, lymphocyte recall responses, cytokine expression, and lymphocyte subpopulations. Following immunization and infection, chickens fed the VAC- or MC-supplemented diets showed increased body weights, greater profilin antibody levels, and/or greater lymphocyte proliferation compared with non-supplemented controls. Prior to Eimeria infection, immunized chickens on the MC-supplemented diet showed reduced IFN-γ and IL-6 levels, but increased expression of TNFSF15, compared with non-supplemented controls. Post-infection levels of IFN-γ and IL-6 were increased, while IL-17F transcripts were decreased, with MC-supplementation. For VAC-supplemented diets, decreased IL-17F and TNFSF15 levels were observed only in infected chickens. Finally, immunized chickens fed the MC-supplemented diet exhibited increased MHC class II(+), CD4(+), CD8(+), TCR1+, or TCR2(+) T cells compared with nonsupplemented controls. Animals on the VAC-containing diet only displayed an increase in K1(+) macrophages. In conclusion, dietary supplementation with VAC or MC alters immune parameters following recombinant protein vaccination against avian coccidiosis.


Subject(s)
Chickens , Coccidiosis/veterinary , Eimeria tenella , Poultry Diseases/prevention & control , Protozoan Vaccines/immunology , Acrolein/analogs & derivatives , Acrolein/pharmacology , Animal Feed , Animal Nutritional Physiological Phenomena , Animals , Antibodies, Protozoan , Capsicum/chemistry , Cell Proliferation , Coccidiosis/prevention & control , Curcuma/chemistry , Cymenes , Cytokines/genetics , Cytokines/metabolism , Dietary Supplements , Feces/parasitology , Gene Expression Regulation , Lymphocytes/drug effects , Lymphocytes/physiology , Monoterpenes/pharmacology , Plant Extracts/chemistry , Plant Extracts/pharmacology , Poultry Diseases/parasitology , Profilins/blood , Profilins/metabolism , RNA, Messenger/genetics , RNA, Messenger/metabolism , Spleen/cytology , Weight Gain/drug effects
13.
Br J Haematol ; 150(4): 463-72, 2010 Aug.
Article in English | MEDLINE | ID: mdl-20618332

ABSTRACT

A proteomic approach was applied to study the protein expression profile of peripheral T-cells derived from patients at the onset of different B-lymphoproliferative diseases, because a rising interest in specific actions played by T-cells in such pathologies has emerged. Decreased levels of profilin-1 and cofilin-1 and increased levels of coronin1A and prohibitin were found in patients, compared with healthy controls. The protein-protein interaction network of these proteins was studied using a web-based bioinformatics tool, highlighting the actin cytoskeleton regulation as the main biological process involved in peripheral T-cells of such patients. Unsupervised cluster analysis of protein expression data shows that the recorded alteration of T-cell proteome was specifically induced by B-cell pathologies.


Subject(s)
Biomarkers, Tumor/blood , Lymphoma, B-Cell/immunology , Neoplasm Proteins/blood , T-Lymphocytes/metabolism , Adult , Aged , Cluster Analysis , Cofilin 1/blood , Female , Humans , Leukemia, Lymphocytic, Chronic, B-Cell/immunology , Male , Middle Aged , Profilins/blood , Proteomics/methods
14.
Biochemistry ; 46(23): 6931-43, 2007 Jun 12.
Article in English | MEDLINE | ID: mdl-17511469

ABSTRACT

The acid-induced unfolding of human platelet profilin (HPP) can be minimally modeled as a three-state process. Equilibrium unfolding studies have been performed on human platelet profilin1 (HPP) and monitored by far-UV circular dichroism, tryptophan fluorescence, ANS binding, and NMR spectroscopy. Far-UV CD measurements obtained by acid titration demonstrate that HPP unfolds via a three-state mechanism (N --> I --> U), with a highly populated intermediate between pH 4 and 5. Approximately 80% of native helical secondary structural content remains at pH 4, as indicated by monitoring the CD signal at 222 nm. The stability (DeltaGH2O) of the native conformation at pH 7.0 (obtained by monitoring the change in tryptophan signal as a function of urea concentration) is 5.56 +/- 0.51 kcal mol-1; however, the DeltaGH2O for the intermediate species at pH 4 is 2.01 +/- 0.47 kcal mol-1. The calculated m-values for the pH 7.0 and pH 4.0 species were 1.64 +/- 0.15 and 1.34 +/- 0.17 kcal mol-1 M-1, respectively, which is an indication that the native and intermediate species are similarly compact. Additionally, translational diffusion measurements obtained by NMR spectroscopy and ANS binding studies are consistent with a globular and compact conformation at both pH 7.0 and 4.0. The pKa values for the two histidine (His) residues located on helix 4 of HPP were determined to be 5.6 and 5.7 pH units. These pKa values coincide with the midpoint of the far-UV CD acid titration curve and suggest that the protonation of one or both His residues may play a role in the formation of the unfolding intermediate. Stable intermediate species populate the 2D 1H-15N HSQC NMR spectra between pH 4 and 5. A number of backbone and side-chain resonances show significant perturbations relative to the native spectrum; however, considerable nativelike tertiary contacts remain. Interestingly, the residues on HPP that are significantly altered at low pH coincide with segments of the G-actin binding surface and poly-l-proline binding interface. The earlier reports that a decrease in pH below 6.0 induces structural alterations in profilin, favoring dissociation of the profilin-actin complex, corresponds with the structural alterations observed in the partially unfolded species. Our findings suggest that a novel mechanism for pH induced disruption of the profilin-G-actin complex involve a nativelike unfolding intermediate of profilin.


Subject(s)
Blood Platelets/physiology , Profilins/blood , Profilins/chemistry , Acid-Base Equilibrium , Amino Acids/analysis , Crystallography, X-Ray , Hydrogen-Ion Concentration , Kinetics , Magnetic Resonance Spectroscopy , Models, Molecular , Profilins/isolation & purification , Protein Conformation
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