Complete amino acid sequence of bovine beta 2-microglobulin.

beta 2-Microglobulin has been isolated and crystallized from bovine colostrum and represents the only crystalline form of this protein reported. The complete sequence of bovine beta 2-microglobulin was determined using only one proteolytic enzyme, Staphylococcus aureus V8 protease. Automated degradation of the intact molecule and two large peptides produced by enzymic digestion provided unequivocal placement of all residues. Bovine beta 2-microglobulin, molecular weight 11,630, contains 98 residues as compared with 99 for the human, rabbit, guinea pig, and murine proteins. The valine residue at position 49 in all the aforementioned species is deleted in the bovine variant. This crystalline protein is also uniquely characterized by three di-prolyl sequences in the first third of the molecule. beta 2-Microglobulin is a highly conserved protein, and in a comparison of absolute amino acid sequence differences among species, bovine beta 2- microglobulin ranges from a low of 24 substitutions as compared with the rabbit homologue and 26 for human to 32 for mouse and guinea pig.