Analysis of gamma beta, beta gamma, gamma gamma, beta beta continuous turns in proteins

We report the observation of continuous turns in proteins which comprise in dividual gamma -turns or beta -turns or both that are situated immediately one after the other along the polypeptide chain. The continuous turns were identified from a representative data set of three-dimensional protein crys tal structures. The gamma beta/beta gamma, gamma gamma and beta beta contin uous turns represent peptides of varying amino acid residue lengths and con formations. The continuous turns frequently observed in proteins were: gamm a beta, between a coil and a strand; beta gamma, between a helix and a stra nd; gamma gamma between coils; and beta beta, either between a strand and a coil or between strands or coils. We determined the statistically signific ant amino acid residue preferences at individual positions in the turn, cal culated amino acid positional potentials and analyzed main chain hydrogen b onds and side-chain interactions likely to stabilize the continuous turns. The data on continuous turns have been integrated in the database of struct ural motifs in proteins (DSMP) on our web server at (http://www.cdfd.org.in /dsmp.html). This is useful to make queries on sequences compatible with di fferent continuous turns.