Mesoderm Development Candidate 1 (MESDC1)

The crystal structure shows a unique fold comprised of a 5- and 4-helix bundle. The 5-helix bundle is composed of non-sequential helices due to insertion of the 4-helix bundle into the loop at the C-terminus of helix α3. The linker connecting the bundles forms a two-stranded anti-parallel β-sheet likely limiting the relative movement of the two bundles. This suggests the 4-helix bundle has a unique role, and its pI (7.8) is higher than other rod domains.

Both helical bundles contain vinculin-binding sites, but that in the isolated 5-helix bundle is cryptic whereas that in the isolated 4-helix bundle is constitutively active. In contrast, both bundles are required for actin binding. Finally, MESDc1 protein, which is predicted to have a similar fold, is a novel actin binding protein.