Cooperative interactions between odorant-binding proteins of Anopheles gambiae

Abstract

To understand olfactory discrimination in Anopheles gambiae, we made six purified recombinant OBPs and investigated their ligand-binding properties. All OBPs were expressed in bacteria with additional production of OBP47 in the yeast Kluveromyces lactis. Ligand-binding experiments, performed with a diverse set of organic compounds, revealed marked differences between the OBPs. Using the fluorescent probe N-phenyl-1-naphthylamine, we also measured the binding curves for binary mixtures of OBPs and obtained, in some cases, unexpected behaviour, which could only be explained by the OBPs forming heterodimers with binding characteristics different from those of the component proteins. This shows that OBPs in mosquitoes can form complexes with novel ligand specificities, thus amplifying the repertoire of OBPs and the number of semiochemicals that can be discriminated. Confirmation of the likely role of heterodimers was demonstrated by in situ hybridisation, suggesting that OBP1 and OBP4 are co-expressed in some antennal sensilla of A. gambiae.

New Insights into the Mechanism of Odorant Detection by the Malaria-transmitting Mosquito Anopheles gambiae

“…1C). That interactions with OBP1 are transmitted to residues that directly interact with the ligand may explain previous observations that the presence of OBP1 and OBP4 can lead to an increase in the binding affinity for a fluorescent dye (33). We conclude that binding of indole to OBP4 results in a significant increase in the conformational stability of residues that are required to allow interactions with OBP1.…”

“…gambiae it was recently demonstrated that perception of indole and 3-methyl-indole requires OBP1 (31), and this may involve the formation of interactions between OBP1 and OBP4 (32,33). This study reveals that binding of indole to OBP4 results in a dramatic conformational ordering that is required to form a binding site for OBP1.…”

“…gambiae OBP1 is required for in vivo responses to indole and 3-methyl indole (31), both of which are major components of incubated human sweat that is attractive to female mosquitoes (3-6). Additional studies have proposed that this response requires the formation of heterodimeric complexes between OBP1 and OBP4 (32,33 …”

“…gambiae OBP1 is required for in vivo responses to indole and 3-methyl indole (31), both of which are major components of incubated human sweat that is attractive to female mosquitoes (3)(4)(5)(6). Additional studies have proposed that this response requires the formation of heterodimeric complexes between OBP1 and OBP4 (32,33). This was based on observations that (a) OBP4 has a higher affinity for indole than OBP1, (b) OBP1 and OBP4 co-localize within sensilla, and (c) OBP4 can cooperatively increase the binding of a fluorescent dye (1-NPN) to OBP1 or OBP3 (33).…”

“…Additional studies have proposed that this response requires the formation of heterodimeric complexes between OBP1 and OBP4 (32,33). This was based on observations that (a) OBP4 has a higher affinity for indole than OBP1, (b) OBP1 and OBP4 co-localize within sensilla, and (c) OBP4 can cooperatively increase the binding of a fluorescent dye (1-NPN) to OBP1 or OBP3 (33). OBP4, OBP1, and OBP3 are the orthologues of the D. melanogaster OBPs LUSH, OS-E, and OS-F respectively, which are known to co-localize within the same sensilla (34).…”