PT  - JOURNAL ARTICLE
AU  - Ryan G. Walker
AU  - Jason C. McCoy
AU  - Magdalena Czepnik
AU  - Melanie J. Mills
AU  - Adam Hagg
AU  - Kelly L. Walton
AU  - Thomas Cotton
AU  - Marko Hyvönen
AU  - Richard T. Lee
AU  - Paul Gregorevic
AU  - Craig A. Harrison
AU  - Thomas B. Thompson
TI  - Molecular characterization of latent GDF8 reveals mechanisms of activation
AID  - 10.1101/155614
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 155614
4099  - http://biorxiv.org/content/early/2017/06/26/155614.short
4100  - http://biorxiv.org/content/early/2017/06/26/155614.full
AB  - Growth/differentiation factor 8 (GDF8) or myostatin negatively regulates of muscle mass. GDF8 is held in a latent state through interactions with its N-terminal prodomain, much like TGF-β. Using a combination of small angle X-ray scattering and mutagenesis, we characterized the interactions of GDF8 with its prodomain. Our results show that the prodomain:GDF8 complex can exist in a fully latent state and an activated or ‘triggered’ state where the prodomain remains in complex with the mature domain. However, these states are not reversible, indicating the latent GDF8 is ‘spring-loaded’. Structural analysis shows that the prodomain:GDF8 complex adopts an ‘open’ configuration, distinct from the latency state of TGF-β and more similar to the ‘open’ state of Activin A and BMP9 (non-latent complexes). We determined that GDF8 maintains similar features for latency, including the alpha-1 helix and fastener elements, and identified a series of mutations in the prodomain of GDF8 that alleviate latency, including I56E, which does not require activation by the protease Tolloid. Activating GDF8 mutations were analyzed in vivo and show increased effects on the muscle (e.g. decreased fiber size) compared to wild-type GDF8. Collectively, these results help characterize the latency and activation mechanisms of GDF8.