Pivotal Molecular Determinants of Peptidic and Collagen Triple Helicase Activities Reside in the S3 Subsite of Matrix

The mechanism of triple helical collagen unwinding and cleavage by collagenases in the matrix metallopro-teinase (MMP) family is complex and remains enigmatic. Recent reports show that triple helicase activity is ini-tiated by the hemopexin C domain of membrane type 1-MMP, whereas catalytically inactive full-length inter-stitial collagenase (MMP-1) exhibits full triple helicase functionality pointing to active site determinants that are needed to complete the triple helicase mechanism. In MMP-8, the neutrophil collagenase, a conserved Gly at the S3 substrate specificity subsite is replaced by Asn188 that forms a highly unusual cis bond with Tyr189, a conserved active site residue in the collagenases. Only in MMP-1 is the S3 Gly also replaced, and there too a cis configured Glu-Tyr occurs. Thus, this high energy pep