Structural and biochemical evaluation of Ceratitiscapitata odorant‐binding protein 22 affinity for odorants involved in intersex communication

Abstract

In insects, odorant‐binding proteins (OBPs) connect the peripheral sensory system to receptors of olfactory organs. Medfly Ceratitis capitata CcapObp22 shows 37% identity and close phylogenetic affinities with Drosophila melanogaster OBP69a/pheromone‐binding protein related protein 1. The CcapObp22 gene is transcribed in the antennae and maxillary palps, suggesting an active role in olfaction. Here, we recombinantly produced CcapObp22, obtaining a 13.5 kDa protein capable of binding multiple strongly hydrophobic terpene compounds, including medfly male pheromone components. The highest binding affinity [half maximal effective concentration (EC50) = 0.48 µM] was to (E,E)‐α‐farnesene, one of the most abundant compounds in the male pheromone blend. This odorant was used in cocrystallization experiments, yielding the structure of CcapOBP22. The monomeric structure shows the typical OBP folding, constituted by six α‐helical elements interconnected by three disulphide bridges. A C‐terminal seventh α‐helix constitutes the wall of a deep, L‐shaped hydrophobic cavity. Analysis of the electron density in this cavity suggested trapping of farnesene in the crystal structure, although with partial occupancy. Superposition of the CcapOBP22 structure with related seven‐helical OBPs highlights striking similarity in the organization of the C‐terminal segment of these proteins. Collectively, our molecular and physiological data on medfly CcapOBP22 suggest its involvement in intersex olfactory communication.

Aedes aegypti Odorant Binding Protein 22 selectively binds fatty acids through a conformational change in its C-terminal tail

“…There are three structures of single domain OBPs that have an additional seventh C-terminal helix; An gambiae OBP7 (PDB 3R1O) 68 , Locusta migratoria OBP1 (LmigOBP1, PDB 4PT1) 69 and the Mediterranean fruit fly, Ceratitis capitate OBP22 (PDB 6NHE) 70 . Of these, AeOBP22 is most similar to LmigOBP1 (Dali Z = 12.1) ( Fig.…”

Characterization of MaltOBP1, a Minus-C Odorant-Binding Protein, From the Japanese Pine Sawyer Beetle, Monochamus alternatus Hope (Coleoptera: Cerambycidae)

“…The C-terminus has been shown to be an important component in binding and releasing OBPs to odorants (Sun et al, 2016). In AmelOBP14 and Ceratitis capitata CcapOBP22, which belong to a class of OBPs that possesses eight cysteines (Plus-C OBPs), the C-terminus segment forms an external seventh helix at the interface between the protein exterior and the internal cavity (Spinelli et al, 2012;Falchetto et al, 2019). However, D. helophoroides DhelOBP21, with a short C-terminus, possesses five helices, unlike other insect OBPs .…”

“…Elevated expression in nonolfactory regions, i.e., leg and wing, suggests that MaltOBP1 participates in other physiological activities in addition to perception and recognition of semiochemicals in M. alternatus. A number of OBPs were found to be expressed in nonolfactory tissues, including head (R. ferrugineus RferOBP7, Yan et al, 2016), thorax (R. ferrugineus RferOBP11, Yan et al, 2016), abdomen (Agrilus mali AmalOBP8, Cui et al, 2018), and palps (C. capitata, CcapOBP22, Falchetto et al, 2019), indicating that these OBPs play other physiological roles. For instance, orthologous OBP10 from two sibling Helicoverpa species was expressed in both chemosensory and reproductive organs, and a function as an oviposition deterrent in Helicoverpa species was suggested, potentially to avoid cannibalism of conspecific larvae (Sun et al, 2012).…”

“…Studies involving OBP identification (Li L. et al, 2017;Zhao et al, 2018), protein structural analysis (Northey et al, 2016;Falchetto et al, 2019), immunocytochemistry in specific olfactory sensilla Zhang et al, 2018), ligand binding properties (Sun et al, 2017(Sun et al, , 2018, and in vivo RNA interference (Yin et al, 2018;He et al, 2019) have demonstrated that insect OBPs play crucial roles in odorant discrimination, binding, and transportation. These proteins carry lipophilic odorants to the olfactory receptor cells in the sensillar lymph surrounding the sensory dendrite (Pelosi et al, 2014(Pelosi et al, , 2018.…”

Identification of olfactory genes and functional analysis of BminCSP and BminOBP21 in Bactrocera minax

“…Odorant binding proteins (OBPs) and chemosensory proteins (CSPs) are typically located on antennae and mouthparts and are also major proteins involved in recognition of volatiles. OBPs and CSPs play an important role in transporting incoming odorants to corresponding receptors and in transferring the odorant-degrading enzymes (ODEs) to the receptors [13, 14]. Previous studies have shown that insects communicate with their environment through detection of odorant molecules [15].…”