THE BACKBONE STRUCTURE OF THE MAJOR COLD-SHOCK PROTEIN CS7.4 OF ESCHERICHIA-COLI IN SOLUTION INCLUDES EXTENSIVE BETA-SHEET STRUCTURE

CS7.4 is the major cold-shock protein specifically expressed to a leve l as high as 13% of the total cellular protein within the first hour w hen Escherichia coli cell culture is shifted from 37 to 15 degrees C [ Goldstein et al. (1990) Proc. Natl. Acad. Sci. USA 87, 283-287]. It co nsists of 70 amino acid residues with a very high content of aromatic residues. CS7.4 was overproduced and purified to homogeneity. Its seco ndary structure was analyzed by examining circular dichroism at both t he far and near-UV regions; the results suggest that the protein is la rgely beta-sheet in conformation. The predominance of beta-sheet struc ture in the protein was confirmed by using Fourier-transform infrared spectroscopy. A folded compact conformation was also verified by fluor escence emission spectroscopy. We evaluated T-m, Delta H, and Delta S from the thermal denaturation profile of the protein. Unusual spectral features observed in the far-UV region are attributed to the high con tent of aromatic residues. The protein is relatively small and contain s no disulfide bonds. However, it is surprisingly stable to heat denat uration.