title: Molten globule-like state of human serum albumin at low pH.
abstract: Human serum albumin (HSA), under conditions of low pH, is known to exist in two isomeric forms, the F form at around pH 4.0 and the E form below 3.0. We studied its conformation in the acid-denatured E form using far-UV and near-UV CD, binding of a hydrophobic probe, 1-anilinonaphthalene-8-sulfonic acid (ANS), thermal transition by far-UV and near-UV CD, tryptophan fluorescence, quenching of tryptophan fluorescence using a neutral quencher, acrylamide and viscosity measurements. The results show that HSA at pH 2.0 is characterized by a significant amount of secondary structure, as evident from far-UV CD spectra. The near-UV CD spectra showed a profound loss of tertiary structure. A marked increase in ANS fluorescence signified extensive solvent exposure of non-polar clusters. The temperature-dependence of both near-UV and far-UV CD signals did not exhibit a co-operative thermal transition. The intrinsic fluorescence and acrylamide quenching of the lone tryptophan residue, Trp214, showed that, in the acid-denatured state, it is buried in the interior in a non-polar environment. Intrinsic viscosity measurements showed that the acid-denatured state is relatively compact compared with that of the denatured state in 7 M guanidine hydrochloride. These results suggest that HSA at pH 2.0 represents the molten globule state, which has been shown previously for a number of proteins under mild denaturing conditions.
authors.affiliation: Interdisciplinary Biotechnology Unit, Aligarh Muslim University, India.
authors.forename: S
authors.initials: S
authors.lastname: Muzammil
authors.forename: Y
authors.initials: Y
authors.lastname: Kumar
authors.forename: S
authors.initials: S
authors.lastname: Tayyab
mesh_terms: D000817:Anilino Naphthalenesulfonates; D002942:Circular Dichroism; D006358:Hot Temperature; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012709:Serum Albumin / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D014783:Viscosity
chemical_list: D000817:Anilino Naphthalenesulfonates; D012709:Serum Albumin; C027132:1-anilino-8-naphthalenesulfonate