Susceptibility of type V collagen to neutral proteases: evidence that the major molecular species is a thrombin-sensitive heteropolymer, [alpha 1(V)]2 alpha 2(V).

The susceptibility of human type V collagen to several neutral proteases was examined. Thrombin cleaved both the alpha 1(V) and alpha 2(V) chains of this protein at 34 degrees C, producing two pairs of fragments with apparent molecular weights of 95000 and 10000 on sodium dodecyl sulfate--polyacrylamide gel electrophoresis. Two-dimensional 125I-labeled peptide mapping of the larger fragments demonstrated that the upper band [which comigrated with alpha 1(I)] was derived from both the alpha 1(V) and alpha 2(V) chains, while the other component [which comigrated with alpha 2(I) was a product of alpha 1(V) alone. Cleavage of type V collagen, containing alpha 3(V) chains, with thrombin produced an analogous pattern with three high molecular weight bands. Chymotrypsin and trypsin cleaved type V collagen at 37 degrees C but not at lower temperatures. Digestion of type V collagen with elastase at 37 degrees C resulted in selective proteolysis of alpha 2(V), leaving alpha 1(V) essentially intact. Pepsin treatment of type V collagen from which alpha 2(V) had been removed by elastase treatment resulted in nearly complete degradation of alpha 1(V). These data support the hypothesis that a major fraction of native type V collagen is a heteropolymer with the chain composition [alpha 1(V)]2 alpha 2(V). Cleavage of type V collagen by thrombin may have physiologic significance in that breakdown of pericellular matrix may be an important step in the response of a tissue to injury.