Specific interactions among odorant-binding proteins of the African malaria vector Anopheles gambiae

In this report we present results from a comprehensive study undertaken toward the identification of proteins interacting with odourant-binding proteins (OBPs) of the African malaria vector Anopheles gambiae with a focus on the interactions among different OBPs. From an initial screen for proteins that interact with a member of the Plus-C group of OBPs, OBP48, which is primarily expressed in female antennae and downregulated after a blood meal, a number of interacting proteins were identified, which included five classic OBPs and OBP48 itself. The interacting OBPs as well as a number of other classic and Plus-C group OBPs that were not identified in the initial screen, were expressed in lepidopteran cells and subsequently examined for in vitro interactions in the absence of exogenously added ligands. Co-immunoprecipitation and chemical cross-linking studies suggest that OBP48 is capable of homodimerizing, heterodimerizing and forming higher order complexes with those examined examples of classical OBPs identified in the initial screen but not with other classical or Plus-C group OBPs that failed to appear in the screen. The latter OBPs are, however, also capable of forming homodimers in vitro and, at least in the case of two examined classic OBPs, heterodimers as well. These results suggest a previously unsuspected potential of nonrandom combinatorial complexity that may be crucial for odour discrimination by the mosquito.