Introduction- Many proteins are composed of several domains. For example, the protein pyruvate kinase has four domains. (Based on 1pkm.pdb, S.C.Allen & H.Muirhead, unpublished)
A HELIX-LOOP-HELIX at the amino terminal.
An EIGHT-STRANDED PARALLEL BETA SHEET, using the beat-alpha-beta motif.
A SEVEN-STRANDED ANTI-PARALLEL BETA SHEET, using the hairpin beta sheet motif.
And a TWISTED FIVE-STRANDED PARALLEL BETA SHEET, using the beta-alpha-beta motif.