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Biophys J, July 2001, p. 455-462, Vol. 81, No. 1

Biophysical Characterization of the Influence of Salt on Tetrameric SecB

Carien Dekker,* Bogos Agianian,dagger Martin Weik,dagger Giuseppe Zaccai,Dagger § Jan Kroon,dagger Piet Gros,dagger and Ben de Kruijff*

 *Department Biochemistry of Membranes, Institute of Biomembranes, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, NL-3584 CH Utrecht, The Netherlands;  dagger Department Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, NL-3584 CH Utrecht, The Netherlands;  Dagger Institut Laue Langevin, F-38042 Grenoble Cedex 9, France;  §Institut de Biologie Structurale CEA-CNRS, F-38027 Grenoble Cedex 1, France

SecB is a tetrameric chaperone, with a monomeric molecular mass of 17 kDa, that is involved in protein translocation in Escherichia coli. It has been hypothesized that SecB undergoes a conformational change as a function of the salt concentration. To gain more insight into the salt-dependent behavior of SecB, we studied the protein in solution by dynamic light scattering, size exclusion chromatography, analytical ultracentrifugation, and small angle neutron scattering. The results clearly demonstrate the large influence of the salt concentration on the behavior of SecB. At high salt concentration, SecB is a non-spherical protein with a radius of gyration of 3.4 nm. At low salt concentration the hydrodynamic radius of the protein is apparently decreased, whereas the ratio of the frictional coefficients is increased. The protein solution behaves in a non-ideal way at low salt concentrations, as was shown by the analytical ultracentrifugation data and a pronounced interparticle effect observed by small angle neutron scattering. A possible explanation is a change in surface charge distribution dependent on the salt concentration in the solvent. We summarize our data in a model for the salt-dependent conformation of tetrameric SecB.

Biophys J, July 2001, p. 455-462, Vol. 81, No. 1
© 2001 by the Biophysical Society   0006-3495/01/07/455/08  $2.00




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Copyright © 2001 by the Biophysical Society.