Identification and cloning of a female antenna-specific odorant-binding protein in the mosquito Culex quinquefasciatus

We have identified and cloned a cDNA encoding the first odorant-binding protein isolated from mosquitoes. The protein isolated from female antennae of Culex quinquefasciatus (CquiOBP) was not detected in legs (control tissue) or in antennal extracts from males, and showed mobility in native polyacrylamide gels similar to that of the pheromone-binding protein from Bombyx mori. The open reading frame of the cloned cDNA encoded a hydrophobic signal peptide (24 residues) and an acid mature protein (pI 5.5) of 125 amino acid residues (calculated molecular mass 14,504 Da). The transcript was detected by RT-PCR with antennal, but not with leg tissues. CquiOPB shared the highest amino acid identity with a product deduced from Drosophila melanogaster PBPRP-3 cDNA (58.6%), OBPs from scarab beetles (35%), and moths (28%). In addition, CquiOBP showed the hallmark of insect odorant-binding proteins, the six Cys residues.