Targeting Aminoglycoside Acetyltransferase Activity of Mycobacterium tuberculosis (H37Rv) Derived Eis (Enhanced Intracellular Survival) Protein with Quercetin.

Eis (Enhanced intracellular survival) protein is an aminoglycoside acetyltransferase enzyme classified under the family - GNAT (GCN5-related family of N-acetyltransferases) secreted by Mycobacterium tuberculosis (Mtb). The enzymatic activity of Eis results in the acetylation of kanamycin, thereby impairing the drug's action. In this study, we expressed and purified recombinant Eis (rEis) to determine the enzymatic activity of Eis and its potential inhibitor. Glide-enhanced precision docking was used to perform molecular docking with chosen ligands. Quercetin was found to interact Eis with a maximum binding affinity of -8.379 kcal/mol as compared to other ligands. Quercetin shows a specific interaction between the positively charged amino acid arginine in Eis and the aromatic ring of quercetin through π-cation interaction. Further, the effect of rEis was studied on the antibiotic activity of kanamycin A in the presence and absence of quercetin. It was observed that the activity of rEis aminoglycoside acetyltransferase decreased with increasing quercetin concentration. The results from the disk diffusion assay confirmed that increasing the concentration of quercetin inhibits the rEis protein activity. In conclusion, quercetin may act as a potential Eis inhibitor.

Antitumor Activity of Taxol Engross Taxol-Caveolin-1 Interaction via Lipid Raft Structure-"Caveolae".

Taxol is one of the most widely used natural antitumor drugs that have shown considerable success in treating cancers of different lineage. However, the development of resistance to taxol is still a significant issue. Caveolae, the cave-like structures found on the surface of many cancerous cells, are enriched in cholesterol and are known to play a pivotal role in drug uptake. Caveolin-1 (Cav-1), the principal structural proteins of the caveolae, interacts with signaling molecules through a scaffolding domain. In the present study, we observed that Cav-1-GFP clusters were instantly recruited to the cell membrane. Interestingly, Caveolae formation followed by internalization was observed after the treatment with time. The recruitment and the formation of the Cav-1-GFP clusters are provided in supplementary video 2 (SV2). The results obtained from molecular docking indicate favorable taxol-Cav-1 interaction. To further confirm the influence of Cav-1 proteins in the uptake and effects of taxol, the cells were treated with beta-cyclodextrin (ß-CD), cholesterol, and taxol combinations. The result suggests that the depletion of cholesterol in HeLa cells makes them less susceptible to taxol at a lower concentration. These observations provide evidence of the interaction between Cav-1 and taxol. Further studies that may elucidate the molecular mechanism of uptake of taxol through caveolae/Cav-1 will help to determine if Cav-1 can be used to increase the uptake of taxol by cancer cells and sensitize the drug-resistant cancer cells to taxol.

Organic osmolyte betaine mitigates the deleterious effects of Diclofenac in vivo in wistar albino rats

Abstract Diclofenac sodium (DF) is a non-steroidal anti-inflammatory drug (NSAID) that possesses antipyretic, analgesic, antinociceptive and anti-inflammatory activities. Like other NSAIDs, DF is known to be associated with renal, cardiovascular, and gastrointestinal complications. The present study was carried out to evaluate the adverse effects of DF in vivo in wistar albino rats and to assess if oral administration of the organic osmolyte betaine mitigates the adverse effect of DF. Eighteen male Wistar rats were divided into three groups, one group of animals was fed orally with 20 mg/kg of DF once/day, and the other group received a combination of 20 mg/kg of DF and 30 mg/kg of betaine, once/day. Apart from the hematological and biochemical parameters, histopathological changes in the liver, lungs, brain, heart and kidney were also investigated. Histopathological alterations that were found in the liver, kidney, and lungs of DF-treated animals were found to be minimal or absent in DF + betaine-treated animals, as compared to untreated control. The results showed that betaine mitigates the adverse effects associated with DF treatment.

Effect of pH on Diclofenac-Lysozyme Interaction: Structural and Functional Aspect.

As a nonsteroidal antiinflammatory drug, diclofenac (DCF) is used in the treatment of a variety of human ailments. It has already been reported that the use of this class of drugs for a longer duration is associated with numerous side effects such as cardiovascular implications, reno-medullary complications, etc. In the present study, the effect of DCF on the structure, stability, and function of lysozyme was studied. The study was designed to examine the effect of DCF only at various pH values. Heat-induced denaturation of lysozyme was analyzed in the presence and absence of various molar concentrations of DCF at different pH values. The values of thermodynamic parameters, the midpoint of denaturation (T m), enthalpy change at T m (ΔH m), constant pressure heat capacity change (ΔC p), and Gibbs energy change at 25°C (ΔG D o), thus obtained under a given set of conditions (pH and molar concentration of DCF), demonstrated the following 1) DCF destabilized lysozyme with respect of T m and ΔG D o at all the pH values, 2) the magnitude of protein destabilization is lesser at acidic pH than at physiological pH, 3) structural changes in lysozyme are less projecting at pH 2.0 than at pH 7.0, and 4) quenching is observed at both pH values. Furthermore, the process of protein destabilization in the presence of DCF is entropically driven.

Immunomodulatory Effects of Jacalin, a Dietary Plant Lectin on the Peripheral Blood Mononuclear Cells (PBMCs).

The tumor microenvironment that refers to the tumor's surroundings is a key modulator of tumor growth and invasion. The tumor-derived signals are known to downregulate the anti-tumor effects of the effector cells present in the TME. Thus, the cross-talk between the tumor cells with the surrounding immune cells helps in evading the tumor surveillance as well as aiding in tumor growth and proliferation. Hence, knowledge regarding the effects of drugs/compound on the tumor-stromal interactions is gaining importance. In the present study, the effects of jacalin, a dietary lectin on the proliferation and cytokine production of peripheral blood mononuclear cells (PBMCs), are investigated. Jacalin was shown to act as a mitogen of PBMCs, the key cytokine secreting immune cells. Also, jacalin initially induced increased mRNA expression of pro-inflammatory cytokine IFN-γ; however, prolonged stimulation of PBMCs resulted in increased expression of anti-inflammatory cytokine, mainly TGF-ß. Furthermore, 6 h jacalin prestimulated PBMCs (Jac-PBMCs) were shown to inhibit HeLa cell proliferation while 24 h Jac-PBMCs were found to favor tumor growth. Thus, it may be postulated that while jacalin initially polarizes the PBMCs to hinder the tumor growth, after a stipulated time point, interaction of jacalin with PBMCs can lead to an immunosuppressive TME that may probably assist in tumor growth and progression.

Designing of a Chimeric Vaccine Using EIS (Rv2416c) Protein Against Mycobacterium tuberculosis H37Rv: an Immunoinformatics Approach.

Mycobacterium tuberculosis (Mtb) is a respiratory pathogen that causes tuberculosis (TB). There are a large number of proteins that are involved in the pathogenesis of TB. Stimulating the immune response against TB is very important to clear the pathogens from host. In the present study, an immunoinformatics conduit is used for designing an epitope based chimeric vaccine against TB. Enhanced intracellular survival (EIS) protein from Mtb is used for designing the chimeric vaccine. One B cell epitope, 8 cytotoxic T lymphocyte (CTL), and 6 helper T lymphocyte (HTL) epitopes were predicted based on the MHC allele binding, immunogenicity, antigenicity, allergenicity, toxicity and IFN epitopes. The selected epitopes were used for chimeric vaccine designing. Furthermore, 3D structure elucidation, structural refinement and validation of the designed chimeric vaccine were carried out. The 3D structure was used for protein-protein docking studies with Toll-like receptor 4 (TLR-4), followed by molecular dynamic simulation (MDS) and the interaction between the chimeric vaccine and TLR-4 complex was verified.

Increased ERK phosphorylation and caveolin-1 expression on K562 human chronic myelogenous leukemia cells by jacalin, a dietary plant lectin.

The potential antitumor effects of jacalin, the plant lectin that specifically recognizes the tumor-associated Thomsen-Friedenreich antigen has been extensively studied. We had earlier reported jacalin to be mitogenic to K562, the Bcr-Abl expressing erythroleukemia cell line. The dearth of studies highlighting the proliferative effects of jacalin and other lectins motivated us to unveil the mechanism underlying the mitogenic effects of jacalin. Caveolin-1 (cav-1) is an integral membrane protein, known to play a crucial role in cell signaling, lipid transport, and membrane trafficking. The role of cav-1 in tumorigenesis is considered to be controversial as it can suppress as well as promote tumor growth, depending on the cellular context. In the present study, we propose that cav-1 plays the central role in the mitogenic effects of jacalin on the K562 cells. In accordance, the mRNA, as well as protein expression of cav-1 was found to be upregulated in the jacalin-treated K562 cells as compared to the untreated control. Further, jacalin stimulation also increased the phosphorylation of ERK and Akt. The rationale that leads to the initial conjecture about cav-1 was that the sequence of jacalin possesses a cav-1-binding site.

Increased Expression of TGF-ß and IFN-γ in Peripheral Blood Mononuclear Cells (PBMCs) Cultured in Conditioned Medium (CM) of K562 Cell Culture.

In the present study, we investigated the effects of conditioned media (CM) collected from the cancer cell lines (K562, MCF-7, and HeLa) on peripheral blood mononuclear cells (PBMCs) isolated from the healthy human blood. The soluble factors in the CM are probably responsible for the differential mRNA expressions of Foxp3, Helios, Neuropilin- 1 (NRP-1), and glycoprotein A repetitions predominant (GARP), along with IFN-γ and TGF-ß in PBMCs cultured with cancer cells CM. The PBMCs cultured with CM of K562 showed increased expression of Foxp3, Helios, NRP-1, GARP, IFN-γ, and TGF-ß compared to PBMCs cultured with CM of MCF-7 and HeLa cells. In addition, the intracellular staining on PBMCs cultured with CM from cell lines were also evaluated for CD4, CD25, Foxp3, Helios, and NRP-1 by multicolor flow cytometry. The expression of CD4+CD25+Foxp3+, CD4+Helios+Foxp3+ and CD+NRP-1+Foxp3+ showed retarded cell population compared to control PBMCs. Our data suggest that soluble factors in CM of cancer cells may trigger the immune response in PBMCs resulting in a systematic response. Further research could lead to the identification of specific soluble factors that are involved in trafficking of cells into the immune cascades, which could be a safe and promising strategy for targeting human cancers.

Differential expression of Helios, Neuropilin-1 and FoxP3 in head and neck squamous cell carcinoma (HNSCC) patients.

In recent years, studies have begun to explore the immune involvement in head and neck tumors. Advanced stage head and neck squamous cell carcinoma (HNSCC) has a poor prognosis with low survival rates with high level of immune infiltrates. Tregs (regulatory T cells) play a crucial role in constructing an immunosuppressive tumor microenvironment. In the present study, we highlighted specific Treg markers and its factors in HNSCC solid tumors and peripheral blood of cancer patients. By histopathology and immunofluorescence staining, we observed differential expression of CD4, CD25, Foxp3, Helios and Neuropilin-1. Further, we analyzed the expression of Foxp3, Helios, Neuropilin-1 and GARP by qPCR and flow cytometry in whole blood and found to be elevated in HNSCC patients in comparison with healthy donors. Additionally, IFN-γ, TGF-ß, IL-6, IL-2, IL-10 and TNF-α expressions were also found to be relatively increased in the head and neck cancer patients when compared with healthy donors. Our findings emphasize that Tregs may be involved in promoting tumor progression. Helios and Neuropilin-1 could be potent markers in identifying subsets of Tregs. Association of soluble factors could sculpture the activity of Tregs. With further research, Treg markers and its associated soluble factors could be employed to block Tregs trafficking to the tumor, thus enlightening a potential strategy for targeting human cancers.

Sub-Micellar Concentration of Sodium Dodecyl Sulphate Prevents Thermal Denaturation Induced Aggregation of Plant Lectin, Jacalin.

The irreversible thermal unfolding of jacalin, the lectin purified from jackfruit seeds was accompanied by aggregation, where intermolecular interactions among the subunits are favoured over intramolecular interactions. The extent of aggregation increased as a function of temperature, time and protein concentration. The anionic surfactant, sodium dodecyl sulphate (SDS) significantly suppressed the formation of aggregates as observed by turbidity measurements and Rayleigh scattering assay. Moreover, far UV-CD spectra indicate that the protein ß sheet transforms into α helical structure, when denatured in the presence of 3 mM SDS. Further, jacalin when heated in the presence of SDS partially retained the hemagglutination activity when jacalin-SDS mixture was diluted to 1:8 factor since 3 mM SDS was found to lyse the red blood cells. Thus, SDS only altered the aggregation behaviour of jacalin by preventing intermolecular hydrogen bonding among the exposed residues but did not completely stabilize the native conformation.

Sustained mitogenic effect on K562 human chronic myelogenous leukemia cells by dietary lectin, jacalin.

Dietary lectins have been shown to affect the proliferation of human cancer cell lines. The anti-proliferative effects of lectins from varied sources have been extensively studied and in some cases, the underlying mechanism has been explored. Except for peanut agglutinin (PNA), the mitogenic effects of no other lectins have been studied in detail. In the present study, we have shown that jacalin, lectin purified from jackfruit (Artocarpus integrifolia) seeds act as a mitogen for K562, the Bcr-Abl expressing erythroleukemia cell line (K562) and the effect was found to be dose dependent. K562 cells remained in the proliferative state for a longer period even after the withdrawal of jacalin stimulation, thus jacalin was found to induce sustained mitogenic effect on K562 cells. Further, conditioned media from K562 cells treated with jacalin were observed to have the similar mitogenic effect even in the presence of galactose. Importantly, galactose which is a known ligand for jacalin will interact with functionally active jacalin present in the conditioned media and neutralise its effect. In addition, jacalin treatment also resulted in increased mRNA expression levels of pro-inflammatory cytokines including IL-1ß, IL-6 and IFN-γ. Our results indicate that jacalin induces secretion of soluble molecules, which maybe responsible for this observed increased proliferation of K562 cells.

Disulfiram suppresses growth of the malignant pleural mesothelioma cells in part by inducing apoptosis.

Dithiocarbamate compound Disulfiram (DSF) that binds with copper and functions as an inhibitor of aldehyde dehydrogenase is a Food and Drug Administration approved agent for treatment of alcoholism. Copper complexed DSF (DSF-Cu) also possesses anti-tumor and chemosensitizing properties; however, its molecular mechanisms of action remain unclear. Here we investigated malignant pleural mesothelioma (MPM) suppressive effects of DSF-Cu and the molecular mechanisms involved. DSF-Cu inhibited growth of the murine as well as human MPM cells in part by increasing levels of ubiquitinated proteins. DSF-Cu exposure stimulated apoptosis in MPM cells that involved activation of stress-activated protein kinases (SAPKs) p38 and JNK1/2, caspase-3, and cleavage of poly-(ADP-ribose)-polymerase, as well as increased expression of sulfatase 1 and apoptosis transducing CARP-1/CCAR1 protein. Gene-array based analyses revealed that DSF-Cu suppressed cell growth and metastasis-promoting genes including matrix metallopeptidase 3 and 10. DSF inhibited MPM cell growth and survival by upregulating cell cycle inhibitor p27Kip1, IGFBP7, and inhibitors of NF-κB such as ABIN 1 and 2 and Inhibitory κB (IκB)α and ß proteins. DSF-Cu promoted cleavage of vimentin, as well as serine-phosphorylation and lysine-63 linked ubiquitination of podoplanin. Administration of 50 mg/kg DSF-Cu by daily i.p injections inhibited growth of murine MPM cell-derived tumors in vivo. Although podoplanin expression often correlates with metastatic disease and poor prognosis, phosphorylation of serines in cytoplasmic domain of podoplanin has recently been shown to interfere with cellular motility and migration signaling. Post-translational modification of podoplanin and cleavage of vimentin by DSF-Cu underscore a metastasis inhibitory property of this agent and together with our in vivo studies underscore its potential as an anti-MPM agent.

CARP-1 functional mimetics are a novel class of small molecule inhibitors of malignant pleural mesothelioma cells.

Malignant pleural mesothelioma (MPM) is an asbestos-related thoracic malignancy that is characterized by late metastases, and resistance to therapeutic modalities. The toxic side-effects of MPM therapies often limit their clinical effectiveness, thus necessitating development of new agents to effectively treat and manage this disease in clinic. CARP-1 functional mimetics (CFMs) are a novel class of compounds that inhibit growth of diverse cancer cell types. Here we investigated MPM cell growth suppression by the CFMs and the molecular mechanisms involved. CFM-1, -4, and -5 inhibited MPM cell growth, in vitro, in part by stimulating apoptosis. Apoptosis by CFM-4 involved activation of pro-apoptotic stress-activated protein kinases (SAPKs) p38 and JNK, elevated CARP-1 expression, cleavage of PARP1, and loss of the oncogene c-myc as well as mitotic cyclin B1. Treatments of MPM cells with CFM-4 resulted in depletion of NF-κB signaling inhibitor ABIN1 and Inhibitory κB (IκB)α and ß, while increasing expression of pro-apoptotic death receptor (DR) 4 protein. CFM-4 enhanced expression of serine-phosphorylated podoplanin and cleavage of vimetin. CFMs also attenuated biological properties of the MPM cells by blocking their abilities to migrate, form colonies in suspension, and invade through the matrix-coated membranes. Both podoplanin and vimentin regulate processes of cell motility and invasion, and their expression often correlates with metastatic disease, and poor prognosis. The fact that phosphorylation of serines in the cytoplasmic domain of podoplanin interferes with processes of cellular motility, CFM-4-dependent elevated phosphorylated podoplanin and cleavage of vimentin underscore a metastasis inhibitory property of these compounds, and suggest that CFMs and/or their future analogs have potential as anti-MPM agents.

Thymoquinone suppression of the human hepatocellular carcinoma cell growth involves inhibition of IL-8 expression, elevated levels of TRAIL receptors, oxidative stress and apoptosis.

Hepatocellular carcinoma (HCC) is the fourth most common solid tumor worldwide. The chemokine interleukin-8 (IL-8) is overexpressed in HCC and is a potential target for therapy. Although the transcription factor NF-κB regulates IL-8 expression, and while thymoquinone (TQ; the most bioactive constituent of black seed oil) inhibits NF-κB activity, the precise mechanisms by which TQ regulates IL-8 and cancer cell growth remain to be clarified. Here, we report that TQ inhibited growth of HCC cells in a dose- and time-dependent manner, caused G2M cell cycle arrest, and stimulated apoptosis. Apoptosis was substantiated by activation of caspase-3 and -9, as well as cleavage of poly(ADP-ribose)polymerase. TQ treatments inhibited expression of NF-κB and suppressed IL-8 and its receptors. TQ treatments caused increased levels of reactive oxygen species (ROS) and mRNAs of oxidative stress-related genes, NQO1 and HO-1. Pretreatment of HepG2 cells with N-acetylcysteine, a scavenger of ROS, prevented TQ-induced cell death. TQ treatment stimulated mRNA expression of pro-apoptotic Bcl-xS and TRAIL death receptors, and inhibited expression of the anti-apoptotic gene Bcl-2. TQ enhanced TRAIL-induced death of HepG2 cells, in part by up-regulating TRAIL death receptors, inhibiting NF-κB and IL-8 and stimulating apoptosis. Altogether, these findings provide insights into the pleiotropic molecular mechanisms of TQ-dependent suppression of HCC cell growth and underscore potential of this compound as anti-HCC drug.

CARP-1 functional mimetics: a novel class of small molecule inhibitors of medulloblastoma cell growth.

Medulloblastomas (MBs) constitute an aggressive class of intracranial pediatric tumors. Current multimodality treatments for MBs include surgery, ionizing radiation, and chemotherapy. Toxic side effects of therapies coupled with high incidence of recurrence and the metastatic spread warrant development of more effective, less toxic therapies for this disease. CARP-1/CCAR1 is a peri-nuclear phospho-protein that is a co-activator of the cell cycle regulatory anaphase promoting complex/cyclosome (APC/C) E3 ligase. CARP-1 functional mimetics (CFMs) are a novel class of small molecule compounds that interfere with CARP-1 binding with APC/C subunit APC-2, and suppress growth of a variety of cancer cells in part by promoting apoptosis. Here we investigated MB growth inhibitory potential of the CFMs and found that CFM-4 inhibits growth of MB cells in part by inducing CARP-1 expression, promoting PARP cleavage, activating pro-apoptotic stress-activated protein kinases (SAPK) p38 and JNK, and apoptosis. Gene-array-based analysis of the CFM-4-treated Daoy MB cells indicated down-regulation of a number of key cell growth and metastasis-promoting genes including cell motility regulating small GTP binding protein p21Rac1, and extracellular matrix metallopeptidase (MMP)-10. Moreover, CFM-4 treatment stimulated expression of a number of molecules such as neurotrophin (NTF)3, and NF-κB signaling inhibitors ABIN1 and 2 proteins. Overexpression of NTF3 resulted in reduced MB cell viability while knock-down of NTF3 interfered with CFM-4-dependent loss of viability. CFMs also attenuated biological properties of the MB cells by blocking their abilities to migrate, form colonies in suspension, and invade through the matrix-coated membranes. Together our data support anti-MB properties of CFM-4, and provide a proof-of-concept basis for further development of CFMs as potential anti-cancer agents for MBs.

Cell cycle and apoptosis regulatory protein (CARP)-1 is expressed in osteoblasts and regulated by PTH.

Bone mass is dependent on osteoblast proliferation, differentiation and life-span of osteoblasts. Parathyroid hormone (PTH) controls osteoblast cell cycle regulatory proteins and suppresses mature osteoblasts apoptosis. Intermittent administration of PTH increases bone mass but the mechanism of action are complex and incompletely understood. Cell Cycle and Apoptosis Regulatory Protein (CARP)-1 (aka CCAR1) is a novel transducer of signaling by diverse agents including cell growth and differentiation factors. To gain further insight into the molecular mechanism, we investigated involvement of CARP-1 in PTH signaling in osteoblasts. Immunostaining studies revealed presence of CARP-1 in osteoblasts and osteocytes, while a minimal to absent levels were noted in the chondrocytes of femora from 10 to 12-week old mice. Treatment of 7-day differentiated MC3T3-E1 clone-4 (MC-4) mouse osteoblastic cells and primary calvarial osteoblasts with PTH for 30min to 5h followed by Western blot analysis showed 2- to 3-fold down-regulation of CARP-1 protein expression in a dose- and time-dependent manner compared to the respective vehicle treated control cells. H-89, a Protein Kinase A (PKA) inhibitor, suppressed PTH action on CARP-1 protein expression indicating PKA-dependent mechanism. PMA, a Protein Kinase C (PKC) agonist, mimicked PTH action, and the PKC inhibitor, GF109203X, partially blocked PTH-dependent downregulation of CARP-1, implying involvement of PKC. U0126, a Mitogen-Activated Protein Kinase (MAPK) Kinase (MEK) inhibitor, failed to interfere with CARP-1 suppression by PTH. In contrast, SB203580, p38 inhibitor, attenuated PTH down-regulation of CARP-1 suggesting that PTH utilized an Extracellular Signal Regulated Kinase (ERK)-independent but p38 dependent pathway to regulate CARP-1 protein expression in osteoblasts. Immunofluorescence staining of differentiated osteoblasts further revealed nuclear to cytoplasmic translocation of CARP-1 protein following PTH treatment. Collectively, our studies identified CARP-1 for the first time in osteoblasts and suggest its potential role in PTH signaling and bone anabolic action.

Relationship between functional activity and protein stability in the presence of all classes of stabilizing osmolytes.

We report the effects of stabilizing osmolytes (low molecular mass organic compounds that raise the midpoint of thermal denaturation) on the stability and function of RNase-A under physiological conditions (pH 6.0 and 25 degrees C). Measurements of Gibbs free energy change at 25 degrees C (DeltaG(D) degrees ) and kinetic parameters, Michaelis constant (K(m)) and catalytic constant (k(cat)) of the enzyme mediated hydrolysis of cytidine monophosphate, enabled us to classify stabilizing osmolytes into three different classes based on their effects on kinetic parameters and protein stability. (a) Polyhydric alcohols and amino acids and their derivatives do not have significant effects on DeltaG(D) degrees and functional activity (K(m) and k(cat)). (b) Methylamines increase DeltaG(D) degrees and k(cat), but decrease K(m). (c) Sugars increase DeltaG(D) degrees , but decrease both K(m) and k(cat). These findings suggest that, among the stabilizing osmolytes, (a) polyols, amino acids and amino acid derivatives are compatible solutes in terms of both stability and function, (b) methylamines are the best refolders (stabilizers), and (c) sugar osmolytes stabilize the protein, but they apparently do not yield functionally active folded molecules.

Glycine betaine may have opposite effects on protein stability at high and low pH values.

The compatible osmolyte glycine betaine (GB) is the most efficient osmoprotectant and best excluder from the protein surface. It can reverse protein aggregation and correct mutant protein defects and counter the harmful effects of urea and salts in vivo and in vitro. In this study we have investigated the pH dependence of the stabilizing effect of GB on three different proteins, namely, alpha-lactalbumin (alpha-LA), lysozyme and ribonuclease-A (RNase-A). We show here that (a) GB stabilizes RNase-A at all pH values, and (b) GB has opposite effects on two proteins at high pH and low pH values, namely, alpha-LA and lysozyme. This conclusion was reached by determining T(m) (midpoint of denaturation), DeltaH(m) (denaturational enthalpy change at T(m)), DeltaC(p) (constant-pressure heat capacity change) and DeltaG(D)(o) (denaturational Gibbs energy change at 25 degrees C) of proteins in the presence of different GB concentrations. Another conclusion of this study is that DeltaH(m) and DeltaC(p) are not significantly changed in the presence of GB. This study suggests that other methylated glycine osmolytes may also behave in the same manner.