NMR analysis of cbEGF domains gives new insights into the structural consequences of a P1148A substitution in fibrillin-1

Fibrillin-1 is a modular glycoprotein and a major component of the 10-12 nm microfibrils of the extracellular matrix. Mutations in the fibrillin-1 (FB N 1) gene result in the connective tissue disease the Marfan syndrome (MFS) and related disorders. The calcium binding EGF-like (cbEGF) domain is the predominant structural motif of the protein and >70% of mutations leading t o MFS disrupt this domain. A missense mutation which changes a proline to a lanine (P1148A) in cbEGF domain 13 has been associated with a number of fib rillin disorders including MFS and Shprintzen-Goldberg syndrome. However, i t has also been described as a polymorphism. In this study comparative NMR analyses on wild-type and mutant forms of covalently-linked fibrillin cbEGF domain pairs have been performed to investigate the structural consequence s of this substitution. A comparison of the two-dimensional NOESY spectra o f the wild-type and mutant forms of cbEGF domains 12 & 13 and cbEGF domains 13 & 14 indicated that the proline to alanine amino acid change does not i ntroduce a significant structural defect into cbEGF domain 13 or the adjace nt domains and most likely represents a polymorphism. These results demonst rate how, in the case of a protein with a well defined domain organisation such as fibrillin-1, comparative NMR analyses can be used to substantiate g enetic evidence for the polymorphic status of an amino acid.