Solution Structure and Dynamics of a Calcium Binding Epidermal Growth Factor-like Domain Pair from the Neonatal Region of Human Fibrillin-1

Fibrillin-1 is a mosaic protein mainly composed of 43 calcium binding epidermal growth factor-like (cbEGF) domains arranged as multiple, tandem repeats. Mutations within the fibrillin-1 gene cause Marfan syndrome (MFS), a heritable disease of connective tissue. More than 60% of MFS-causing mutations identified are localized to cbEGFs, emphasizing that the native properties of these domains are critical for fibrillin-1 function. The cbEGF12–13 domain pair is within the longest run of cbEGFs, and many mutations that cluster in this region are associated with severe, neonatal MFS. The NMR solution structure of Ca 2+ -loaded cbEGF12–13 exhibits a near-linear, rod-like arrangement of domains. This observation supports the hypothesis that all fibrillin-1 (cb)EGF-cbEGF pairs, characterized by a single interdomain linker residue, possess this rod-like structure. The domain arrangement of cbEGF12–13 is stabilized by additional interdomain packing interactions to those observed for cbEGF32–33, which may help to explain the previously reported higher calcium binding affinity of cbEGF13. Based on this structure, a model of cbEGF11–15 that encompasses all known neonatal MFS missense mutations has highlighted a potential binding region. Backbone dynamics data confirm the extended structure of cbEGF12–13 and lend support to the hypothesis that a correlation exists between backbone flexibility and cbEGF domain calcium affinity. These results provide important insight into the potential consequences of MFS-associated mutations for the assembly and biomechanical properties of connective tissue microfibrils.