The transmembrane endopeptidase ADAM10 is a critical catalyst for the regulated proteolysis of key drivers of mammalian development and physiology. As the primary human α-secretase, it is also responsible for non-amyloidogenic cleavage of APP. ADAM10 function requires the formation of a complex with one of six C8-tetraspanin (Tspan) proteins, which promote ADAM10 maturation and surface export. The identity of the bound Tspan also appears to modulate the selection of substrates for ADAM10 cleavage, with Tspan15 favoring N-cadherin and Tspan5 and Tspan14 directing ADAM10 cleavage of Notch. Here, we present single particle cryo-EM structures of three different Tspan-ADAM10 complexes captured in three functional states of the ADAM10 protein lifecycle. In the Tspan14-ADAM10 zymogen complex, the ADAM10 prodomain conceals the enzyme active site. In complexes of Tspan5 and Tspan14 with mature ADAM10, the enzyme adopts a closed conformation similar to that of the isolated ADAM10 ectodomain, masking the enzyme active site. In complexes of the Tspans determined in the presence of an active-site directed inhibitor, the enzyme adopts an open conformation with the active site above the plasma membrane poised for membrane-proximal substrate cleavage. In the Tspan15-ADAM10 complex, a secondary interface of Tspan15 with the ADAM10 catalytic domain holds the active site 20 angstroms above the membrane, a different secondary interface positions the active site roughly 30 angstroms above the membrane in the Tspan14-ADAM10 complex, and there is no secondary interface constraining the ADAM10 active site in the Tspan5-ADAM10 complex. Strikingly, each Tspan places the ADAM10 active site at different distances from the membrane, providing a molecular rationale for the distinct substrate selectivity of different ADAM10-Tspan complexes. This work also offers a molecular roadmap for targeted modulation of ADAM10 activity for therapeutic purposes.
Stephen C. Blacklow (Sun,) studied this question.