title: Heterogeneity of equilibrium molten globule state of cytochrome c induced by weak salt denaturants under physiological condition.
abstract: While many proteins are recognized to undergo folding via intermediate(s), the heterogeneity of equilibrium folding intermediate(s) along the folding pathway is less understood. In our present study, FTIR spectroscopy, far- and near-UV circular dichroism (CD), ANS and tryptophan fluorescence, near IR absorbance spectroscopy and dynamic light scattering (DLS) were used to study the structural and thermodynamic characteristics of the native (N), denatured (D) and intermediate state (X) of goat cytochorme c (cyt-c) induced by weak salt denaturants (LiBr, LiCl and LiClO4) at pH 6.0 and 25°C. The LiBr-induced denaturation of cyt-c measured by Soret absorption (Δε400) and CD ([θ]409), is a three-step process, N ↔ X ↔ D. It is observed that the X state obtained along the denaturation pathway of cyt-c possesses common structural and thermodynamic characteristics of the molten globule (MG) state. The MG state of cyt-c induced by LiBr is compared for its structural and thermodynamic parameters with those found in other solvent conditions such as LiCl, LiClO4 and acidic pH. Our observations suggest: (1) that the LiBr-induced MG state of cyt-c retains the native Met80-Fe(III) axial bond and Trp59-propionate interactions; (2) that LiBr-induced MG state of cyt-c is more compact retaining the hydrophobic interactions in comparison to the MG states induced by LiCl, LiClO4 and 0.5 M NaCl at pH 2.0; and (3) that there exists heterogeneity of equilibrium intermediates along the unfolding pathway of cyt-c as highly ordered (X1), classical (X2) and disordered (X3), i.e., D ↔ X3 ↔ X2 ↔ X1 ↔ N.
authors: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, Jamia Nagar, New Delhi, 110025, India.
authors: Hamidur
authors: H
authors: Rahaman
authors: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, Jamia Nagar, New Delhi, 110025, India.
authors: Md Khurshid
authors: MK
authors: Alam Khan
authors: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, Jamia Nagar, New Delhi, 110025, India.
authors: Md Imtaiyaz
authors: MI
authors: Hassan
authors: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, Jamia Nagar, New Delhi, 110025, India.
authors: Asimul
authors: A
authors: Islam
authors: Institute of Biochemistry and Biophysics, University of Tehran, Tehran, Iran.
authors: Ali Akbar
authors: AA
authors: Moosavi-Movahedi
authors: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, Jamia Nagar, New Delhi, 110025, India.
authors: Faizan
authors: F
authors: Ahmad
mesh_terms: D000818:Animals; D002942:Circular Dichroism; D045304:Cytochromes c / Q000737:chemistry* / Q000378:metabolism*; D006041:Goats; D006321:Heart / Q000502:physiology*; D018020:Lithium Compounds / Q000494:pharmacology*; D011487:Protein Conformation; D011489:Protein Denaturation / Q000187:drug effects*; D017510:Protein Folding / Q000187:drug effects*; D017550:Spectroscopy, Fourier Transform Infrared; D013816:Thermodynamics
chemical_list: D018020:Lithium Compounds; D045304:Cytochromes c