A high performance prediction system of coiled coil domains containing heptad breaks: SOSUIcoil

The coiled coil structure in proteins is characterized by heptad repeats of hydrophobic amino acids, but many breaks of the heptad repeats are observed within coiled coil regions which are the main cause of the errors in the currently used prediction systems for coiled coils. For understanding the characteristics of coiled coils including heptad breaks, the features of coiled coils were studies focusing on three problems: (1) the determination of appropriate register for the breaks in heptad repeat regions, (2) the discriminations of coiled coil regions using physical properties of amino acid segments which have heptad repeats and (3) the elucidation of the structural difference among several types of heptad breaks. Appropriate registers of heptad repeats and breaks were determined by two steps: first, the typical template of heptad repeats was applied to amino acid sequences and then several types of template for heptad breaks were applied to the segments around inconsistent points of the heptad repeat regions, leading to the most appropriate registers. Then, the coiled coil regions were discriminated from other types of regions by the canonical discriminant analysis, using ten parameters (three physicochemical properties and seven number densities of amino acids). The novel coiled coil prediction system SOSUIcoil showed better performances of coiled coil prediction than other prediction systems. Furthermore, the structures of segments around the heptad breaks were analyzed, indicating that some types of heptad breaks tend to form coiled coil structure whereas the other types are at the end of coiled coils.