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