Cell surface-associated proteins which bind native type IV collagen or gelatin.

Gelatin coupled to Sepharose has been used to isolate [35S]methionine-labeled polypeptides of Mr = 47,000, 56,000, 62,000, and 65,000 from the 12,000 X g supernatant of detergent extracts of mouse embryo parietal endoderm cells. The polypeptides can also be recovered from various established cell lines which synthesize type IV procollagen, and in these cells the Mr = 47,000 polypeptide is the major gelatin-binding component. Several lines of evidence, including the results of continuous labeling and pulse-chase experiments, show that the polypeptides are not derived by proteolytic cleavage of larger precursors and are distinct from fragments of fibronectin. The Mr = 47,000, 62,000, and 65,000 polypeptides all contain N-linked oligosaccharide side chains, as judged by their labeling with [3H]mannose and their sensitivity to tunicamycin. The Mr = 62,000 and 65,000 polypeptides can be resolved by two-dimensional gel electrophoresis into species with different isoelectric points, and the Mr = 47,000 has a pI of 7.5-8.0. None of the gelatin-binding polypeptides appear to accumulate in the culture medium, and the Mr = 47,000, 62,000, and 65,000 species are labeled in a lactoperoxidase-catalyzed iodination of intact cells, suggesting that they are associated with the cell surface. Only the Mr = 47,000 glycoprotein binds to native type IV collagen. Possible functions for these surface components in vivo are discussed.