Sidekick Homolog 1, Cell Adhesion Molecule (SDK1)

The Sdk proteins were concentrated at synaptic sites, and Sdk-positive synapses were restricted to the 2 (of at least 10) sublaminae to which Sdk-expressing cells projected. Ectopic expression of Sdk in Sdk-negative cells redirected their processes to an Sdk-positive sublamina.

These results implicated Sdks as determinants of lamina-specific synaptic connectivity. The predicted vertebrate, Drosophila, and C. elegans SDK proteins are similar in size and share an identical domain structure. From N to C terminus, each SDK protein contains a signal sequence, 6 immunoglobulin C2 motifs, 13 fibronectin type III motifs, a single transmembrane domain, and an approximately 200-amino acid cytoplasmic domain. A C-terminal hexapeptide, GFSSFV, is conserved in all SDKs.