Primary structure of the bovine beta-crystallin Bp chain. Internal duplication and homology with gamma-crystallin.

The major polypeptide chain of bovine beta-crystallin, beta Bp, was fragmented by means of cyanogen bromide treatment and by enzymatic digestions. Manual and automated Edman degradation of the resulting peptides provided the complete amino acid sequence of the beta Bp chain. The N-terminal alanine residue was shown to be N-alpha-acetylated by mass spectrometry. The chain has a length of 204 residues and a calculated molecular weight of 23210. There is a considerable degree of homology between the N-terminal and C-terminal halves of the chain, presumably reflecting a tandem duplication of a shorter ancestral gene. The sequence of beta Bp is sufficiently related to that of gamma-crystallin II to place these proteins in the same superfamily. No sequence relationship was found with the alpha-crystallin chains.