Regulation of human ADAM 12 protease by the prodomain - Evidence for a functional, cysteine switch

The ADAMs (a disintegrin and metalloprotease) are a family of multidomain p roteins that are believed to play key roles in cell-cell and cell-matrix in teractions, We have shown recently that human ADAM 12-S (meltrin alpha) is an active metalloprotease. It is synthesized as a zymogen, with the prodoma in maintaining the protease in a latent form. We now provide evidence that the latency mechanism of ADAM 12 can be explained by the cysteine switch mo del, in which coordination of Zn2+ in the active site of the catalytic doma in by a cysteine residue in the prodomain is critical for inhibition of the protease. Replacing Cys(179) with other amino acids results in an ADAM 12 preform that is proteolytically active, but latency can be restored by plac ing cysteine at other positions in the propeptide, None of the amino acids adjacent to the crucial cysteine residue is essential for blocking activity of the protease domain. In addition to its latency function, the prodomain is required for exit of ADAM 12 protease from the endoplasmic reticulum, T issue inhibitor of metalloprotease-l, -2, and -3 were not found to block pr oteolytic activity of ADAM 12, hence a physiological inhibitor of ADAM 12 p rotease in the extracellular environment remains to be identified.