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Biophys. J. BioFAST: First Published January 27, 2006. doi:10.1529/biophysj.105.071050
© 2006 by the Biophysical Society.

A more recent version of this article appeared on April 15, 2006.
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Stina Lindman
Wei-Feng Xue
Olga Szczepankiewicz
Mikael C. Bauer
Hanna Nilsson
Sara Linse
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PROTEINS

Salting the Charged Surface - pH and Salt Dependence of Protein G B1 Stability

Stina Lindman 1*, Wei-Feng Xue 1, Olga Szczepankiewicz 1, Mikael C. Bauer 1, Hanna Nilsson 1 and Sara Linse 1

1 Lund University

* To whom correspondence should be addressed. E-mail: stina.lindman{at}bpc.lu.se.

Submitted on August 1, 2005
Revised on September 8, 2005
Accepted on 29 December 2005


  Abstract
The present study shows significant effects of protein surface charges on stability and these effects are not eliminated by salt screening. The stability for a variant of protein G B1 domain was studied in the pH-range of 1.5-11 at low, 0.15M and 2M salt. The variant has three mutations; T2Q, N8D, N37D; to guarantee an intact covalent chain at all pH-values. The stability of the protein shows distinct pH dependence with the highest stability close to the isoelectric point. The stability is pH dependent at all three NaCl-concentrations indicating that interactions involving charged residues are important at all three conditions. We find that 2M salt stabilizes the protein at low pH (protein net charge is +6 and total number of charges is 6) but not at high pH (net charge is ≤-6 and total number of charges is ≥18). Furthermore, 0.15M salt slightly decreases the stability of the protein over the pH-range. The results show that a net charge of the protein is destabilizing and indicate that proteins contain charges for other reasons than improved stability. Salt seems to reduce the electrostatic contributions to stability under conditions with few total charges but cannot eliminate electrostatic effects in highly charged systems.

Key Words: PGB1, electrostatic interactions, global analysis, protein folding, protein stability




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S. Lindman, S. Linse, F. A. A. Mulder, and I. Andre
pKa Values for Side-Chain Carboxyl Groups of a PGB1 Variant Explain Salt and pH-Dependent Stability
Biophys. J., January 1, 2007; 92(1): 257 - 266.
[Abstract] [Full Text] [PDF]


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Copyright © 2006 by the Biophysical Society.