期刊
PROTEIN SCIENCE
卷 10, 期 12, 页码 2485-2497出版社
WILEY
DOI: 10.1110/ps.ps.20801
关键词
preferential interactions; protein water-accessible surface area; protein folding; Hofmeister Series; urea; guanidinium chloride; guanidinium thiocyanate; peptide backbone
资金
- NIGMS NIH HHS [T32 GM008349, GM47022, R01 GM047022, 5 T32 GMO8349] Funding Source: Medline
To interpret effects of urea and guanidiniurn (GuH(+)) salts on processes that involve large changes in protein water- accessible surface area (ASA), and to predict these effects from structural information,, a thermodynamic characterization of the interactions of these solutes with different types of protein surface is required. In the present work we quantify the interactions of urea, GuHCl, GuHSCN, and, for comparison, KCI with native bovine serum albumin (BSA) surface, using vapor pressure osmometry (VPO) to obtain preferential interaction coefficients (Gamma (mu 3)) as functions of nondenaturing concentrations of these solutes (0-1 molal). From analysis of Gamma (mu 3) using the local-bulk domain model, we obtain concentration-independent partition coefficients K-P(nat) that characterize the accumulation of these solutes near native protein (BSA) surface: K-P,urea(nat) = 1.10 +/- 0.04, K-P,SCN-(nat) = 2.4 +/- 0,2, K-P,GuH+(nat) = 1.60 +/- 0.08, relative to K-P,K+(nat) equivalent to 1 and K-P,Cl-(nat) = 1.0 +/- 0.08. The relative magnitudes of K-P(nat) are consistent with the relative effectiveness of these solutes as perturbants of protein processes. From a comparison of partition coefficients for these solutes and native surface (K-P(nat)) with those determined by us previously for unfolded protein and alanine-based peptide surface K-P(unf) we dissect K-P into contributions from polar peptide backbone and other types of protein surface. For globular protein-urea interactions, we find K-P,urea(nat) = K-P,urea .(unf). We propose that this equality arises because polar peptide backbone is the same fraction (0. 13) of total ASA for both classes of surface. The analysis presented here quantifies and provides a physical basis for understanding Hofmcister effects of salt ions and the effects of uncharged solutes on protein processes in terms of K-P and the change in protein ASA.
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