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Effects of molecular crowding by saccharides on α‐chymotrypsin dimerization
Author(s) -
Patel Chetan N.,
Noble Schroeder M.,
Weatherly Gresham T.,
Tripathy Ashutosh,
Winzor Donald J.,
Pielak Gary J.
Publication year - 2002
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.4450102
Subject(s) - osmolyte , chemistry , chymotrypsin , dimer , trypsin , lysozyme , biochemistry , stereochemistry , biophysics , enzyme , organic chemistry , biology
Given the importance of protein complexes as therapeutic targets, it is necessary to understand the physical chemistry of these interactions under the crowded conditions that exist in cells. We have used sedimentation equilibrium to quantify the enhancement of the reversible homodimerization of α‐chymotrypsin by high concentrations of the osmolytes glucose, sucrose, and raffinose. In an attempt to rationalize the osmolyte‐mediated stabilization of the α‐chymotrypsin homodimer, we have used models based on binding interactions (transfer‐free energy analysis) and steric interactions (excluded volume theory) to predict the stabilization. Although transfer‐free energy analysis predicts reasonably well the relatively small stabilization observed for complex formation between cytochrome c and cytochrome c peroxidase, as well as that between bobtail quail lysozyme and a monoclonal Fab fragment, it underestimates the sugar‐mediated stabilization of the α‐chymotrypsin dimer. Although predictions based on excluded volume theory overestimate the stabilization, it would seem that a major determinant in the observed stabilization of the α‐chymotrypsin homodimer is the thermodynamic nonideality arising from molecular crowding by the three small sugars.