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Studies on the Acid Induced Unfolding of Human Serum Albumin

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Abstract:

The acid induced unfolding of HSA (Human Serum Albumin) was studied using UV-difference spectroscopy, fluorescence spectroscopy and far-UV CD spectroscopy. In UV-difference spectroscopy, the molar extinction coefficient decreased from N state to F state. Partially buried Tyr residues are transferred from a medium of high polarizability (native N state ) to a medium of low polarizability (F state). This is followed by loss of two electrostatic interactions Lys 205- Glu 465 and Arg218-Asp451 or one electrostatic interaction Lys205-Glu 465 / Arg218-Asp451 and one buried carboxyl group of acidic amino acid. Similarly, UV-difference spectroscopy showed a decrease in absorbance in F&8652;E transition due to exposure of completely buried tyrosine residues from medium of high polarizability (F state) to a medium of low polarizability (E state). This is also followed by loss of one electrostatic interaction out of three electrostatic interactions namely, Asp187-Lys432, Asp187-Lys521 and Lys190-Glu425. The tryptophanyl fluorescence spectra showed that the N&8652;F transition is accompanied by a decrease in fluorescence intensity. This implies that there is partial exposure of Trp214 to aqueous environment. Consequently, there is a loss of two electrostatic interactions Lys 205-Glu 465 and Arg218-Asp451 or one electrostatic interaction Lys205-Glu 465 / Arg218-Asp451 and one buried carboxyl group of acidic amino acid in N&8652;F transition. The tryptophanyl fluorescence spectroscopy also showed that partially exposed Trp214 residue becomes nearly completely exposed in F&8652;E transition. This is also followed by loss of two electrostatic interactions out of three Asp 187-Lys432,Asp187-Arg521 and Lys190-Glu425 in F&8652;E transition. Taken together, these results showed that in N&8652;F and F&8652;E transitions a different number of electrostatic interaction is detected by different techniques. Secondly, in both N&8652;F and F&8652;E transitions, chromophoric groups are exposed first to aqueous environment and this is followed by loss of electrostatic interactions.





Keywords: Acid induced unfolding; F&8652;E transition; N&8652;F transition; UV-difference spectroscopy; far-UV CD spectroscopy; fluorescence spectroscopy

Document Type: Research Article

DOI: http://dx.doi.org/10.2174/092986609787601750

Publication date: March 1, 2009

More about this publication?
  • Protein & Peptide Letters publishes short papers in all important aspects of protein and peptide research, including structural studies, recombinant expression, function, synthesis, enzymology, immunology, molecular modeling, drug design etc. Manuscripts must have a significant element of novelty, timeliness and urgency that merit rapid publication. Reports of crystallisation, and preliminary structure determinations of biologically important proteins are acceptable. Purely theoretical papers are also acceptable provided they provide new insight into the principles of protein/peptide structure and function.
ben/ppl/2009/00000016/00000003/art00017
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