Fibrillin microfibril structure identifies long-range effects of inherited pathogenic mutations affecting a key regulatory TGFβ-binding site

Genetic mutations in fibrillin microfibrils cause a range of serious inherited diseases such as Marfan syndrome (MFS) and Weill-Marchesani syndrome (WMS). These diseases typically show major dysregulation of tissue development and growth, particularly in skeletal long bones, but links between the mutations and the diseases are unknown. In this study we reveal the detailed cryo-EM structure of native fibrillin microfibrils from mammalian tissue. The major bead region showed pseudo 8-fold symmetry and a buried protease resistant N-terminal core. Based on this structure, we show a WMS deletion mutant induces a rearrangement with long-range effects blocking interaction with latent TGFβ-binding protein (LTBP)-1 at a remote site. Separate deletion of this binding site resulted in the assembly of shorter fibrillin microfibrils with structural alterations. These results establish that in complex extracellular protein assemblies, such as in fibrillin, mutations may have long-range structural consequences to disrupt growth factor signalling and cause disease.