Characterization of SMOC-2, a modular extracellular calcium-binding protein.

We have isolated the novel gene SMOC-2, which encodes a secreted modular protein containing an EF-hand calcium-binding domain homologous to that in BM-40. It further consists of two thyroglobulin-like domains, a follistatin-like domain and a novel domain found only in the homologous SMOC-1. Phylogenetic analysis of the calcium-binding domain sequences showed that SMOC-1 and -2 form a separate group within the BM-40 family. The human and mouse SMOC-2 sequences are coded for by genes consisting of 13 exons located on chromosomes 6 and 17, respectively. Analysis of recombinantly expressed protein showed that SMOC-2 is a glycoprotein with a calcium-dependent conformation. Results from Northern blots and reverse transcription PCR revealed a widespread expression in many tissues.