RESUMEN
Bone morphogenetic protein 1 (BMP-1), which is a tolloid member of the astacin-like family of zinc metalloproteinases, is a highly effective procollagen C-proteinase (PCP) and chordinase. On the other hand, mammalian tolloid like-2 (mTLL-2) does not cleave chordin or procollagen; procollagen is cleaved by mTLL-2 in the presence of high levels of procollagen C-proteinase enhancer-1 (PCPE-1), for reasons that are unknown. We used these differences in activity between BMP-1 and mTLL-2 to narrow in on the domains in BMP-1 that specify PCP and chordinase activity. Using a domain swap approach, we showed that: 1) the metalloproteinase and CUB2 domains of BMP-1 are absolutely required for PCP activity; swaps with either of the corresponding domains in BMP-1 and mTLL-2 did not result in procollagen cleavage and 2) the proteinase domain of mTLL-2 can cleave chordin if coupled to the CUB1 domain of BMP-1. Therefore, the minimal structure for chordinase activity comprises a metalloproteinase domain (either from BMP-1 or from mTLL-2) and the CUB1 domain of BMP-1 (the CUB1 domain of mTLL-2 cannot substitute for the CUB1 domain of BMP-1). We showed that the minimal procollagen C-proteinase (BMP-1 lacking the EGF and CUB3 domain) was enhanced by PCPE-1 but not as well as BMP-1 retaining the CUB3 domain. Further studies showed that PCPE-1 had no effect on the ability of BMP-1 to cleave chordin. The data support a previously suggested mechanism of PCPE-1 whereby PCPE-1 interacts with procollagen, but in addition, the CUB3 domain of BMP-1 appears to augment the interaction.