title: Testing the dependence of stabilizing effect of osmolytes on the fractional increase in the accessible surface area on thermal and chemical denaturations of proteins.
abstract: Here we have generated two different denatured states using heat- and guanidinium chloride (GdmCl)-induced denaturations of three disulfide bond free proteins (barstar, cytochrome-c and myoglobin). We have observed that these two denatured states of barstar and myoglobin are structurally and energetically different, for, heat-induced denatured state contains many un-melted residual structure that has a significant amount of secondary and tertiary interactions. We show that structural properties of the denatured state determine the magnitude of the protein stabilization in terms of Gibbs free energy change (ΔGD°) induced by an osmolyte, i.e., the greater the exposed surface area, the greater is the stabilization. Furthermore, we predicted the m-values (ability of osmolyte to fold or unfold proteins) using Tanford's transfer-free energy model for the transfer of proteins to osmolyte solutions. We observed that, for each protein, m-value is comparable with our experimental data in cases of TMAO (trimethylamine-N-oxide) and sarcosine. However, a significant discrepancy between predicted and experimental m-values were observed in the case of glycine-betaine.
authors.affiliation: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, New Delhi, 110025, India.
authors.forename: Safikur
authors.initials: S
authors.lastname: Rahman
authors.affiliation: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, New Delhi, 110025, India.
authors.forename: Syed Ausaf
authors.initials: SA
authors.lastname: Ali
authors.affiliation: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, New Delhi, 110025, India.
authors.forename: Asimul
authors.initials: A
authors.lastname: Islam
authors.affiliation: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, New Delhi, 110025, India.
authors.forename: Md Imtaiyaz
authors.initials: MI
authors.lastname: Hassan
authors.affiliation: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, New Delhi, 110025, India. Electronic address: fahmad@jmi.ac.in.
authors.forename: Faizan
authors.initials: F
authors.lastname: Ahmad
mesh_terms: D003198:Computer Simulation; D008956:Models, Chemical; D008958:Models, Molecular; D009995:Osmosis; D009997:Osmotic Pressure; D011487:Protein Conformation; D011489:Protein Denaturation; D011506:Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D013499:Surface Properties; D013696:Temperature; D013816:Thermodynamics
chemical_list: D011506:Proteins
keywords: Accessible surface area; Gibbs free energy; Methylamines; Osmolytes; Protein stabilization