Open AccessMolten globule‐like state of human serum albumin at low pH
Author(s) -
Muzammil Salman,
Kumar Yogesh,
Tayyab Saad
Publication year - 1999
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1327.1999.00810.x
Subject(s) - chemistry , tryptophan , molten globule , guanidine , fluorescence , acrylamide , quenching (fluorescence) , human serum albumin , viscosity , crystallography , analytical chemistry (journal) , chromatography , amino acid , organic chemistry , circular dichroism , biochemistry , monomer , physics , quantum mechanics , polymer
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.