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Osmolytes stabilize Ribonuclease S by stabilizing its fragments S protein and S peptide to compact folding-competent states

Ratnaparkhi, Girish S and Varadarajan, R (2001) Osmolytes stabilize Ribonuclease S by stabilizing its fragments S protein and S peptide to compact folding-competent states. In: Journal of Biological Chemistry, 276 (31). pp. 28789-28798.

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Abstract

Osmolytes stabilize proteins to thermal and chemical denaturation. We have studied the effects of the osmolytes sarcosine, betaine, trimethylamine-N-oxide and taurine on the structure and stability of the protein:peptide complex RNase S using X-ray crystallography and titration calorimetry respectively. The stability of RNase S in a given osmolyte is directly correlated with the ability of the osmolyte to stabilize compact forms of S pro and S pep, the protein and peptide components of the RNase S complex. The largest degree of stabilization is achieved with 6 M sarcosine which increases the denaturation temperatures of RNase S and S pro by 24.6 and $17.4 ^oC$ respectively at pH 5 and protects both proteins against tryptic cleavage. Four crystal structures of RNase S in the presence of different osmolytes do not offer any evidence for osmolyte binding to the folded state of the protein or any perturbation in the water structure surrounding the protein. The degree of stabilization in 6M sarcosine increases with temperature, ranging from -0.52 kcal $mol ^{-1}$ at $20^oC$ to -5.4 kcal $mol ^{-1}$ at $60 ^oC$. The data support the thesis that osmolytes which stabilize proteins, do so by perturbing unfolded states, which change conformation to a compact, folding competent state in the presence of osmolyte. The increased stabilization thus results from a decrease in conformational entropy of the unfolded state.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to American Society for Biochemistry and Molecular Biology.
Keywords: Ribonuclease;Sarcosine;Calorimetry;Crystal structure
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited: 15 Oct 2007
Last Modified: 19 Sep 2010 04:39
URI: http://eprints.iisc.ernet.in/id/eprint/12012

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