PT - JOURNAL ARTICLE AU - Viet Q. Le AU - Roxana E. Iacob AU - Yuan Tian AU - William McConaughy AU - Justin Jackson AU - Yang Su AU - Bo Zhao AU - John R. Engen AU - Michelle Pirruccello-Straub AU - Timothy A. Springer TI - Tolloid cleavage activates latent GDF8 by priming the pro-complex for dissociation AID - 10.1101/154823 DP - 2017 Jan 01 TA - bioRxiv PG - 154823 4099 - http://biorxiv.org/content/early/2017/08/03/154823.short 4100 - http://biorxiv.org/content/early/2017/08/03/154823.full AB - Growth differentiation factor 8 (GDF8)/Myostatin is a latent TGF­β family member that potently inhibits skeletal muscle growth. Here, we compared the conformation and dynamics of precursor, latent, and Tolloid­cleaved GDF8 pro­complexes to understand structural mechanisms underlying latency and activation of GDF8. Negative stain electron microscopy (EM) of precursor and latent pro­complexes reveals a V­shaped conformation that is unaltered by furin cleavage and sharply contrasts with the ring­like, cross­armed conformation of latent TGF­β1. Surprisingly, Tolloid­cleaved GDF8 does not immediately dissociate, but in EM exhibits structural heterogeneity consistent with partial dissociation. Hydrogen–deuterium exchange was not affected by furin cleavage. In contrast, Tolloid cleavage, in the absence of prodomain–growth factor dissociation, increased exchange in regions that correspond in pro-TGF-β1 to the α1-helix, latency lasso, and β1 strand in the prodomain and to the β6’–7’ strands in the growth factor. Thus, these regions are important in maintaining GDF8 latency. Our results show that Tolloid cleavage activates latent GDF8 by destabilizing specific prodomain–growth factor interfaces and primes the growth factor for release from the prodomain.