Growth differentiation factor 8 (GDF8)/myostatin is a latent TGF-β family member that potently inhibits skeletal muscle growth. Here， we compared the conformation and dynamics of precursor， latent， and Tolloid-cleaved GDF8 pro-complexes to understand structural mechanisms underlying latency and activation of GDF8. Negative stain electron microscopy (EM) of precursor and latent pro-complexes reveals a V-shaped conformation that is unaltered by furin cleavage and sharply contrasts with the ring-like， cross-armed conformation of latent TGF-β1. Surprisingly， Tolloid-cleaved GDF8 does not immediately dissociate， but in EM exhibits structural heterogeneity consistent with partial dissociation. Hydrogen-... More
Growth differentiation factor 8 (GDF8)/myostatin is a latent TGF-β family member that potently inhibits skeletal muscle growth. Here， we compared the conformation and dynamics of precursor， latent， and Tolloid-cleaved GDF8 pro-complexes to understand structural mechanisms underlying latency and activation of GDF8. Negative stain electron microscopy (EM) of precursor and latent pro-complexes reveals a V-shaped conformation that is unaltered by furin cleavage and sharply contrasts with the ring-like， cross-armed conformation of latent TGF-β1. Surprisingly， Tolloid-cleaved 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'- and β7'-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.
