Structural basis for the contribution of latent TGFβ binding protein to TGFβ latency and activation.

Transforming growth factor-β (TGFβ) is a potent cytokine that controls all aspects of cellular behavior. TGFβ is secreted in complex with its prodomain and latent TGFβ-binding protein-1 (LTBP1), forming the large latent complex (LLC), which through interaction with the extracellular matrix enables integrin-mediated activation. Although TGFβ structures are known, the influence of LTBP1 on the structure and activity of TGFβ is unknown. Here, we report the LLC cryo-EM structure comprising the LTBP1 eight-cysteine domain covalently bound to TGFβ, revealing a hydrophobic interface between TGFβ and LTBP1. Structure-guided mutagenesis shows that the interface is important for complex formation and TGFβ activity. Our structure supports a contralateral domain swapped architecture in the LLC, and simulations show that this architecture requires increased force to overcome barriers for integrin-mediated activation, while the covalent attachment of TGFβ to LTBP1 redistributes force to reduce unfolding barriers. These insights will be important for therapeutic strategies targeting TGFβ.