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Publication Abstract from PubMed

Myostatin (or growth/differentiation factor 8 [GDF8]) is a member of the transforming growth factor beta (TGF-beta) superfamily of growth factors and negatively regulates skeletal muscle growth. Its dysregulation is implicated in muscle wasting diseases. SRK-015 is a clinical-stage monoclonal antibody that prevents extracellular proteolytic activation of pro- and latent myostatin. Here, we used integrated structural and biochemical approaches to elucidate the molecular mechanism of an antibody-mediated neutralization of pro-myostatin activation. The crystal structure of pro-myostatin in complex with 29H4-16 Fab, a high-affinity variant of SRK-015, at 2.79 A resolution revealed that the antibody binds to a conformational epitope in the arm region of the prodomain distant from the proteolytic cleavage sites. This epitope is highly sequence divergent, sharing only limited similarity to other closely related members of the TGF-beta superfamily. Hydrogen/deuterium exchange-MS experiments indicated that antibody binding induces conformational changes in pro- and latent myostatin that span the arm region, the loops contiguous to the protease cleavage sites, and the latency-associated structural elements. Moreover, negative-stain EM with full-length antibodies disclosed a stable, ring-like antigen-antibody structure in which the two Fab arms of a single antibody occupy the two arm regions of the prodomain in the pro- and latent myostatin homodimers, suggesting a 1:1 (antibody:myostatin homodimer) binding stoichiometry. These results suggest that SRK-015 binding stabilizes the latent conformation and limits the accessibility of protease cleavage sites within the prodomain. These findings shed light on approaches that specifically block the extracellular activation of growth factors by targeting their precursor forms.

Structural basis for specific inhibition of extracellular activation of pro- or latent myostatin by the monoclonal antibody SRK-015.,Dagbay KB, Treece E, Streich FC Jr, Jackson JW, Faucette RR, Nikiforov A, Lin SC, Boston CJ, Nicholls SB, Capili AD, Carven GJ J Biol Chem. 2020 Feb 19. pii: RA119.012293. doi: 10.1074/jbc.RA119.012293. PMID:32075906^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.