Cloning of a new human gene with short consensus repeats using the EST database

M. Nangaku, Stuart J. Shankland, Kiyoshi Kurokawa, Karol Bomsztyk, Richard J. Johnson, William G. Couser

The complement system, which provides many of the effector functions of humoral immunity and inflammation, is tightly regulated by various complement regulatory proteins. The most common structural feature of these proteins is a motif called short consensus repeat (SCR). In order to identify a new human complement regulatory protein, we performed a similarity search using SCR on the expressed sequence tag (EST) database and found a partial sequence of a new human gene. Using a probe containing this partial sequence, we obtained a full-length cDNA of this gene from a human umbilical vein endothelial cell (HUVEC) library. The sequencing reaction demonstrated an open reading frame of 1383 nucleotides coding for a 461 amino acid polypeptide with a deduced relative molecular mass of 51 000. Structural analysis showed that the protein has three SCRs with one transmembrane domain. A characteristic feature of these SCR was that they have six conserved cysteines per repeat instead of the usual four. Therefore, we named this cDNA THECY (three hexa-cysteine motifs). A six cysteine motif is a characteristic feature of selectins. We used northern blot analysis to show that a 2.0 kilobase (kb) transcript was ubiquitously present in most organs studied, and the mRNA was most abundant in the heart. In conclusion, we discovered a member of a new class of membrane-bound SCR-containing molecules using the EST database. Utilization of the EST database may be useful in the search for other new immunological proteins. The function of this gene remains to be elucidated.