Effect of pH and phosphate ions on self-association properties of the major cold-shock protein from Bacillus subtilis.

The intermolecular interactions of the major cold-shock protein from Bacillus subtilis (CspB) in solution in the presence of different salts, including phosphate, have been studied by means of scanning calorimetry and size-exclusion chromatography. Calorimetric results indicate that, in all cases, protein unfolding can be approximated by a 2-state model, but the modes of unfolding can differ depending on the conditions. In the presence of phosphate, the cooperative folding unit is a monomer, whereas in the absence of phosphate, the cooperative unit is a dimer. The difference in the self-association of CspB in the presence and absence of phosphate was supported by size-exclusion chromatography. These results are compared with recent structural studies of CspB in crystal and in solution.