Three-dimensional structure and Molecular Evolution of Tandem repeals within Ice Nucleation Proteins

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Certain bacteria nucleate the crystallization of ice. The ice-nucleation activity is conferred by a protein (ice nucleation protein ; INP). The amino acid sequences of the INPs with molecular weights near 120kDa have a central repeating domain (comprising approximately 81% of the total sequence). The repeating domain consists of tandem repeats with the consensus sequence of AxxxSxxx. The structure of the INPs is still unknown. The purpose of the present study is to investigate the evolution and the structure of the INPs. First, we performed, comparative sequence analysis of ten INPs in details. The analysis revealed that the repeating domain is separated into four subdomains (R^c, R^1, R^2 and R^N). On the basis of this result, the evolutionary history was discussed. Secondly, we performed NMR experiments of synthetic peptide H-SGLRSVLTAGYGSSLISGRRSSLT-OH corresponding to sections of the R^N subdomain. The NMR results indicated the presence of a loop conformation in the sequence of LTAGY.