Greek key motif

This motif is formed by 4 beta-strands. In the example shown, which is from an immunoglobulin protein, the strands are ordered
3-2-1-4 and they are all anti-parallel. As is often the case with Greek keys, all four strands are not in the same sheet. 3 and 2 are in one sheet, and 1 and 4 are in another.

Refined structure of an intact IgG2a monoclonal antibody.
Harris, L.J., Larson, S.B., Hasel, K.W., McPherson, A.
(1997) Biochemistry 36: 1581-1597

(PubMed)

1igt (PDB)

(Strand 2 has a beta-bulge, and I had to use a trick to get Jmol to show it as a continuous beta-strand.)

Greek key design