The 160k alpha 1(IV) chain, a short form of a type IV collagen polypeptide, of bovine lens capsule retains the NC1 domain.

Abstract

We recently reported that the bovine lens capsule contained a shorter alpha 1(IV) chain (160k) as a major polypeptide in addition to the 180k alpha 1(IV) chain [J. Biochem. (1995) 117, 1298-1304]. Two experiments were performed to examine whether or not the 160k polypeptide retained the carboxyl-terminal NC1 domain. On immunoblotting analysis with a monoclonal antibody (H11) raised against the NC1 domain of the human alpha 1(IV) chain [positions 1643-1650; near the carboxyl-terminal end of the human alpha 1(IV) chain], the 180k and 160k polypeptides showed identical immunoreactivity, suggesting that the two chains had the same human alpha 1(IV) collagen NC1 domain sequence. Another monoclonal antibody (H21) specific for the NC1 domain of human alpha 2(IV) did not react with these polypeptides, but with the bands corresponding to 175k and 155k. The 160k polypeptide was selectively solubilized from bovine lens capsules, leaving the other major polypeptides, 180k and 175k, insoluble. The 160k polypeptide was separated by preparative electrophoresis. Bacterial collagenase digestion of the separated 160k polypeptide produced collagenase-resistant segments of about 29k and 30k in size based on globular standards. These sizes corresponded well with those of the NC1 domains of type IV collagen alpha chains (25-30k). The results indicated that the 160k polypeptide retained the carboxyl-terminal NC1 domain of the alpha 1(IV) chain. In turn, the 20k polypeptide of the amino-terminal region or the 7S domain of 180k alpha 1(IV) would have been excised to yield 160k alpha 1(IV), assuming that the 160k alpha 1(IV) chain is a processed form of the 180k alpha 1(IV) one and not an alternatively spliced chain of the alpha 1(IV) gene.