The Anopheles gambiae D7-related are a cluster of salivary genes involved in blood feeding and belong to the insect odorant-binding protein superfamily.

The salivary glands of the mosquito Anopheles gambiae, the most important vector of human malaria, are an interesting target organ for molecular entomology studies both in virtue of their role in pathogen transmission and for the large variety of pharmacological activities which they secrete (anti-hemostatics, immuno-modulators, etc.). We started a few years ago a detailed molecular analysis of the An. gambiae salivary glands and, using the Signal Sequence Trap (SST) technique, we identified 22 novel genes which are either specifically expressed in the salivary glands or whose expression is highly enriched in female glands (1, 2). Among these are the platelet inhibitor apyrase (3), putative anticoagulants (cE5, gSG6, gSG7), a novel family of proteins that we named glandins, an insect Antigen 5 family member (gVAG) and a group of four D7-related salivary proteins (4). The D7-related (D7r) are similar in sequence to the Aedes aegypti D7 and form a cluster of closely linked genes located in a 6 kb region on chromosome arm 3R. Their function is still unknown but they are specifically and abundantly expressed in adult female salivary glands, suggesting that they probably play some essential role in blood-feeding. The D7r belong to a highly divergent family of proteins that is widely spread in blood-sucking Diptera (5) and they can be aligned, in virtue of four highly conserved cysteine residues, to an heterogeneous group of insect proteins belonging to the odorant-binding proteins superfamily. Despite the low sequence identity two members of this family, the Tenebrio molitor THP12 and the Bombyx mori pheromone-binding protein, share a similar tridimensional structure and are organized in six alfa-helices folded to delimit a pocket where small hydrophobic ligands can bind. Sequence comparison and secondary structure prediction analysis suggest that the D7r proteins may adopt a very similar folding and, therefore, may facilitate blood feeding by carrying or binding small hydrophobic molecules. (1) Arcà B et al, 1999 PNAS USA, 96: 1516-21. (2) Lanfrancotti A et al, 2002 FEBS Letters, 517: 67-71. (3) Lombardo F et al, 2000 JBC, 275: 23861-68. (4) Arcà B et al, 2002 Insect Mol Biol, 11:47-55. (5) Valenzuela J et al, 2002 Insect Mol Biol, 11: 149-155.