Chondroitin 4-sulfate covalently cross-links the chains of the human blood protein pre-alpha-inhibitor

The human blood protein pre-alpha-inhibitor is composed of one heavy and one light protein chain. The chains are covalently linked to each other by a structure that has not previously been described, which we designate a protein-glycosaminoglycan-protein (PGP) cross-link. A combination of protein and carbohydrate analytical techniques indicates that the interchain linkage is mediated by a chondroitin 4-sulfate glycosaminoglycan that originates from a typical O-glycosidic link to Ser-10 of the light chain. The heavy chain is esterified, via the alpha-carbon of its C-terminal Asp, to C-6 of an internal N-acetylgalactosamine of the glycosaminoglycan chain. This PGP cross-link may be present in other proteins, but could have been overlooked due to the heterogeneous behavior of proteins containing glycosaminoglycan.