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A novel super-secondary structure of beta-proteins. A triple-strand corner.

A novel super-secondary structure of beta-proteins, denoted here as a triple-strand corner, is considered in this paper. This structure can be represented as an antiparallel triple-strand beta-sheet folded on itself so that the two beta-beta-hairpins are packed approximately orthogonally in different layers and the central strand bends by 90 degrees in the right-handed direction when passing from one layer to the other. In all the triple-strand corners observed in proteins, the first beta-beta-hairpins are right-handed and the second ones are left-handed when viewed from the concave sides of the corners. Arrangement of other beta-strands in the proteins involving the triple-strand corners is also examined.