Single-chain structure of human ceruloplasmin: the complete amino acid sequence of the whole molecule.

Abstract

The amino acid sequence of the amino-terminal 67,000-dalton (67-kDa [kilodaltons]) fragment of human ceruloplasmin was determined and overlapping sequences were established between the 67-kDa and 50-kDa, and between the 50-kDa and 19-kDa fragments. The 67-kDa fragment contains 480 amino acid residues and 3 glucosamine oligosaccharides. These results together with previous sequence data for the 50-kDa and 19-kDa fragments complete the amino acid sequence of human ceruloplasmin. The polypeptide chain has a total of 1046 amino acid residues (MW 120,085) and has attachment sites for 4 glucosamine oligosaccharides; together these account for the total molecular mass of human ceruloplasmin (132 kDa). The sequence analysis of the peptides overlapping the fragments showed that 1 additional amino acid, arginine, is present between the 67-kDa and 50-kDa fragments, and another, lysine, is between the 50-kDa and 19-kDa fragments. Only 2 apparent sites of amino acid interchange have been identified in the polypeptide chain. Both involve a single-point interchange of glycine and lysine that would result in a difference in charge. The results of the complete sequence analysis verified that human ceruloplasmin is composed of a single polypeptide chain and that the subunit-like fragments are produced by proteolytic cleavage during purification (and possibly also in vivo).