Odorant Binding Proteins (OBPs) and Odorant Receptors (ORs) of Anopheles stephensi: Identification and comparative insights

Abstract

Anopheles stephensi is an important vector of malaria in the South Asia, the Middle East, and Eastern Africa. The olfactory system of An. stephensi plays an important role in host-seeking, oviposition, and feeding. Odorant binding proteins (OBPs) are globular proteins that play a pivotal role in insect olfaction by transporting semiochemicals through the sensillum lymph to odorant receptors (ORs). Custom motifs designed from annotated OBPs of Aedes aegypti, Drosophila melanogaster, and Anopheles gambiae were used for the identification of putative OBPs from protein sequences of the An. stephensi Indian strain. Further, BLASTp was also performed to identify missing OBPs and ORs. Subsequently, the presence of domains common to OBPs was confirmed. Identified OBPs were further classified into three sub-classes. Phylogenetic and syntenic analyses were carried out to find homology, and thus the evolutionary relationship between An. stephensi OBPs and ORs with those of An. gambiae, Ae. aegypti and D. melanogaster. Gene structure and physicochemical properties of the OBPs and ORs were also predicted. A total of 44 OBPs and 45 ORs were predicted from the protein sequences of An. stephensi. OBPs were further classified into the classic (27), atypical (10) and plus-C (7) OBP subclasses. The phylogeny revealed close relationship of An. stephensi OBPs and ORs with An. gambiae homologs whereas only five OBPs and two ORs of An. stephensi were related to Ae. aegypti OBPs and ORs, respectively. However, D. melanogaster OBPs and ORs were distantly rooted. Synteny analyses showed the presence of collinear block between the OBPs and ORs of An. stephensi and An. gambiae as well as Ae. aegypti’s. No homology was found with D. melanogaster OBPs and ORs. As an important component of the olfactory system, correctly identifying a species’ OBPs and ORs provide a valuable resource for downstream translational research that will ultimately aim to better control the malaria vector An. stephensi.

Ligand-binding properties of XaffOBP9, a Minus-C odorant-binding protein from Xyleborus affinis (Coleoptera: Curculionidae: Scolytinae)

“…Insects rely on their sensitive olfactory system to detect plant volatiles and pheromones ( Hansson and Stensmyr, 2011 ; Deisig et al, 2012 ), but the specific molecular mechanisms of olfaction in X. affinis for locating hosts have not been fully understood. Identifying the proteins responsible for olfactory perception is crucial to further comprehending the molecular mechanisms of the olfactory system ( Clark and Ray, 2016 ; Zafar et al, 2022 ).…”

“…These findings suggest that these proteins are evolutionarily conserved and may have similar biological functions. Classic OBPs, characterized by six cysteine residues, form three disulfide bonds that are crucial in creating the binding pocket and stabilizing the three-dimensional structure ( Zhang et al, 2011 ; Pelosi et al, 2014 ; Zafar et al, 2022 ). Previous studies suggested that the loss of one disulfide bridge in minus-C OBPs might have functional relevance, as it could generate a more flexible structure ( Vieira and Rozas, 2011 ; Li et al, 2015 ; Zheng et al, 2016 ).…”

“…According to the number of conserved cysteine residues, insect OBPs are categorized into four distinct types. These types are “Classic OBPs” (with six conserved cysteines), “Minus-C OBPs” (with four conserved cysteines), “Plus-C OBPs” (with eight conserved cysteines), and “Atypical OBPs” (with more than eight conserved cysteines) ( Ha and Smith, 2022 ; Zafar et al, 2022 ). The connectivity of disulfide bridges creates an interior hydrophobic pocket for binding lipophilic ligands ( Pelosi et al, 2014 ; Zhang et al, 2020 ).…”

Nonlinear SAR Modelling of Mosquito Repellents for Skin Application

“…Modelling approaches are suited to reach this goal. They allow us to discover original structural scaffolds with a repellent activity and also better understand the mechanisms of action of new and existing repellents [15,55,56].…”