Crystal structure of a novel type of odorant binding protein from Anopheles gambiae, belonging to the C+ class
Résumé
Anopheles gambiae (Agam) relies on its olfactory system to target human prey, leading eventually to injection of Plasmodium falciparum, the malaria vector. Odorant-binding proteins (OBPs) are the first line of proteins involved in odorant recognition. They interact with olfactory receptors and thus constitute an interesting target for insect control. We undertook a large-scale study of proteins belonging to the olfactory system of Agam with the aim of preventing insect bites by designing strong olfactory repellents. We determined the 3D structures of several Agam OBPs alone or in complex with model compounds. Here, we report the first 3D structure of a member of the OBP C+ class, AgamOBP47, which has a longer sequence than classical OBPs and contains 6 disulphide bridges. AgamOBP47 possesses a core of six a-helices and three disulphide bridges, similar to the classical OBP fold. Two extra loops and the N- and C-terminal extra segments contain two additional a-helices and are maintained together by three disulphide bridges. They are embrace the classical OBP core domain. The binding site of OBP47 is located between the core and the additional domains. Two crevices are observed on opposite sides of OBP47, which are joined together by a shallow channel of sufficient size to accommodate a model of the best tested ligand. The binding sites of C+ class OBPs exhibit therefore different characteristics of their binding site, as compared to classical OBPs, which should leave to markedly diverse functional implications.
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