Identification and purification of a family of dimeric major cold shock protein homologs from the psychrotrophic Bacillus cereus WSBC 10201

Whole-cell protein patterns of a psychrotrophic Bacillus cereus strain from cultures grown at 7 and 30°C were compared. This analysis revealed that at least three major proteins are expressed at a significantly higher rate at 7°C than at 30°C. The most abundant of these cold-induced proteins was a small polypeptide of 7.5 kDa, designated CspA, of B. cereus. In addition, four small proteins very similar in size to CspA were seen on both 7°C and 30°C two-dimensional protein gels. Immunoblot analysis using B. cereus anti- CspA antibodies indicated that the five proteins described above plus an additional sixth protein not visible on silver-stained two-dimensional gels are members of a B. cereus cold shock protein family. This hypothesis was corroborated by cloning and sequencing of the genes encoding five proteins of this family. The protein sequences deduced are highly similar and show homology to small procaryotic cold shock proteins and to the cold shock domain of eucaryotic Y-box proteins. Besides CspA, only one of the additional five CspA homologs was slightly cold inducible. In the presence of 100 mM NaCl, the two purified members of the protein family (CspA and CspE) elute as dimers at an apparent molecular mass of 15 kDa from a gel filtration column. At higher salt concentrations, they dissociate into their monomers. Their ability to bind to the ATTGG motif of single-stranded oligonucleotides was demonstrated by band shift analysis.