CHARACTERIZATION OF A NOVEL COLLAGEN CHAIN IN HUMAN-PLACENTA AND ITS RELATION TO AB-COLLAGEN

A novel collagen chain, termed αC, has been isolated from human placenta by limited pepsin digestion. The collagen containing the aC chain copurifies with placental AB collagen during selective salt precipitation but is virtually absent from fetal birth membranes, which contain relatively larger amounts of AB. Both native AB and aC-containing collagens are resistant to human skin collagenase under conditions that support cleavage of type I by greater than 90%. The αC chain was separated from αB by phosphocellulose chromatography and subsequently from aA by chromatography on CM-cellulose. Its amino acid composition is distinct from aA and aB although all three chains possess compo-sitional features in common; the carbohydrate content of the aC chain was intermediate between those of αA and αB. Analysis by NaDodSO4-polyacrylamide gel electrophoresis of peptides produced by CNBr cleavage and by limited digestion with the enzyme mast cell protease indicated different and unique products for the aA, αB, and αC chains. The data support the existence of another collagen chain which is related to the αA and αB chains but which is structurally unique. The proteins containing these chains may in turn comprise a subfamily of collagen isotypes which represents a divergence from and/or specialization of the type IV basement membrane collagens. © 1979, American Chemical Society. All rights reserved.