A general method to assess similarity of protein structures, with applications to T4 bacteriophage lysozyme

A method is proposed that permits the structural similarity between any pair of proteins to be analyzed in a completely general manner. In the proposed procedure, all possible structural segments of a given length from one protein are compared with all possible segments from the other protein. This set of comparisons reveals any structural similarities between the two proteins being compared, and also provides a basis for estimating the probability that a particular degree of structural homology could have occurred by chance. Application of the method to the comparison of T4 bacteriophage lysozyme and carp calcium-binding protein suggests that the previously reported structural similarity between parts of these two proteins [Tufty, R. M.& Kretsinger, R. H. (1975) Science 187, 167-169] is no better than would be expected by chance. On the other hand, the structural correspondence between phage lysozyme and hen egg-white lysozyme [Rossman, M.G. & Argos, P. (1976) J. Mol. Biol. 105, 75-96] does appear to be significant.