Solution NMR structure of the cold-shock protein from the hyperthermophilic bacterium Thermotoga maritima

Cold-shock proteins (Csps) are a subgroup of the cold-induced proteins pref erentially expressed in bacteria and other organisms on reduction of the gr owth temperature below the physiological temperature. They are related to t he cold-shock domain found in eukaryotes and are some of the most conserved proteins known. Their exact function is still not known, but translational regulation, possibly via RNA chaperoning, has been discussed. Here we present the structure of a hyperthermophilic member of the Csp fami ly. The NMR solution structure of TmCsp from Thermotoga maritima, the hyper thermophilic member of this class of proteins, was solved on the basis of 1 015 conformational constraints. It contains five beta strands combined in t wo antiparallel beta sheets making up a beta barrel structure, in which bet a strands 1-4 are arranged in a Greek-key topology. The side chain of R2, w hich is exclusively found in thermophilic members of the Csp family, probab ly participates in a peripheral ion cluster involving residues D20, R2, E47 and K63, suggesting that the thermostability of TmCsp is based on the peri pheral ion cluster around the side chain of R2.