Biological and structural characterizations of mutations in X-linked spondyloepiphyseal dysplasia tarda

Abstract

Spondyloepiphyseal dysplasia tarda (SEDT), an X-linked genetic disease manifesting itself in a disproportionate skeletal structure, is caused by mutations in the SEDL gene. Four missense mutations (S73L, V130D, F83S, and D47Y) have been identified by molecular diagnosis as disease-causing SEDT. Nevertheless, how SEDL mutations disrupt the skeletal structure and cause disease remains unknown. We report here the cloning, expression, and characterization of three different missense mutations (S73L, V130D, and D47Y) in mouse SEDL. The overexpression of the D47Y mutation was mainly observed in the supernatant but those of the S73L and V130D mutations are shown in the insoluble pellets. The substitution of the S73L mutation induces the exposure to hydrophobic amino acids and causes aggregation. That of V130D might break hydrophobic interaction and decrease the secondary structure. The CD spectra of three mutants (S73L, V130D, and D47Y) showed that the a-helices decreased more than that of wild-type SEDL. The F83S (stop) mutant might suggest a large conformational change as the mutant V130D. In order to visualize conformational changes in mutated structures, we used molecular modeling techniques minimizing the total energy. These results could provide the biological characterization and conformational information of the SEDL mutants and suggest the clinical severity of the disorder among human SEDL patients.