A domain structure common to hemopexin, vitronectin, interstitial collagenase, and a collagenase homolog

The sequence of hemopexin consists almost entirely of two homologous domains joined by a short hinge region; the domain structure, with its own characteristic features, is derived from four short tandem repeats. Each repeat contains several alternating clusters of hydrophobic and hydrophilic residues but also has some individual features as a consequence of its position in the domain. Here we present evidence for the presence of a single hemopexin domain in an interstitial collagenase and in a collagenase homolog, as well as of two copies of the domain in vitronectin. The functions of all of these proteins involve binding to various proteins and smaller molecules. We suggest that the presence of this domain may facilitate these binding activities. Our analysis also suggests a tentative identification of substrate-binding and catalytic domains in the collagenase and its homolog.