The backbone structure of the major cold-shock protein CS7.4 of Escherichia coli in solution includes extensive β-sheet structure

Abstract

CS7.4 is the major cold-shock protein specifically expressed to a level as high as 13% of the total cellular protein within the first hour when Escherichia coli cell culture is shifted from 37 to 15°C [Goldstein et al. (1990) Proc. Natl. Acad. Sci. USA 87, 283-287]. It consists of 70 amino acid residues with a very high content of aromatic residues. CS7.4 was overproduced and purified to homogeneity. Its secondary structure was analyzed by examining circular dichroism at both the far and near-UV regions; the results suggest that the protein is largely β-sheet in conformation. The predominance of β-sheet structure in the protein was confirmed by using Fourier-transform infrared spectroscopy. A folded compact conformation was also verified by fluorescence emission spectroscopy. We evaluated Tm, δH, and δS from the thermal denaturation profile of the protein. Unusual spectral features observed in the far-UV region are attributed to the high content of aromatic residues. The protein is relatively small and contains no disulfide bonds. However, it is surprisingly stable to heat denaturation. © 1993 BY THE JOURNAL OF BIOCHEMISTRY.