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. 2022 Mar 22;17(3):e0265896.
doi: 10.1371/journal.pone.0265896. eCollection 2022.

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

Zeeshan Zafar  1 , Sidra Fatima  1 , Muhammad Faraz Bhatti  1 , Farooq A Shah  2 , Zack Saud  3 , Tariq M Butt  3
Affiliations

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

Zeeshan Zafar et al. PLoS One. .

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.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Pipeline of the methodology.
Pipeline of the methodology used for this study is represented.
Fig 2
Fig 2. Chromosomal location of Odorant Binding Proteins (OBPs).
AsteOBPs are shown based on their position on chromosomes of the An. stephensi. Chromosome 2 contained highest number of OBP genes. Some OBPs are clustered on the chromosomes.
Fig 3
Fig 3. Chromosomal location of Odorant Receptors (ORs).
Position of the OR genes is shown on the chromosomes of the An. stephensi. Chromosome 2 contained highest number of OR genes. Some ORs are clustered on the chromosomes.
Fig 4
Fig 4. Multiple sequence alignment of the OBPs.
Multiple Sequence Alignment of the OBPs is shown in figure. Conserved motifs have been highlighted in all three classes of the OBPs: Classic, atypical and plus-C OBPs.
Fig 5
Fig 5. Phylogenetic analysis of OBPs.
Phylogenetic analysis of the OBPs of Anopheles stephensi, Anopheles gambiae, Aedes aegypti and Drosophila melanogaster were carried out using FastTree 2. An. stephensi OBPs showed closer relationship to An. gambiae OBPs. The bootstrap values have been represented in the figure.
Fig 6
Fig 6. Phylogenetic analysis of ORs.
Phylogenetic analysis of Anopheles stephensi, Anopheles gambiae, Aedes aegypti and Drosophila melanogaster ORs were carried out using FastTree 2 on galaxy web server. An. stephensi ORs showed closer relationship to An. gambiae ORs. The bootstrap values have been represented in the figure.
Fig 7
Fig 7. Synteny analysis of OBPs.
Synteny analysis were carried out to find the collinear blocks between the OBPs of An. stephensi and OBPs of (A) Ae. aegypti and (B) Ae. gambiae. Chromosomes and chromosomal position of the OBPs have been shown. Green lines (A) show the syntenic relationship between the OBPs of An. stephensi and Ae. aegypti whereas blue lines (B) represent the syntenic relationship between the OBPs of An. stephensi and An. gambiae.
Fig 8
Fig 8. Synteny analysis of ORs.
Synteny analysis were carried out to find the collinear blocks between the ORs of An. stephensi and ORs of (A) Ae. aegypti and (B) Ae. gambiae. Chromosomes and chromosomal position of the ORs have been shown along with the lines showing synteny between the ORs. Red lines represent the syntenic relationship between the ORs of An. stephensi with Ae. aegypti (A) and An. gambiae (B).
Fig 9
Fig 9. Gene structure of the OBPs.
Conserved MEME motifs (A), Pfam domains (B) and UTR/CDS (C) are shown. Conserved motifs are present in all the OBPs along with the gene structure. Presence of UTRs and CDS is shown in genes.
Fig 10
Fig 10. Gene structure of the ORs.
Conserved MEME motifs (A), Pfam domains (B) and UTR/CDS (C) are represented in the figure. Structural domain 7tm_6 of the odorant receptors is present in all the ORs. Whereas some sequences lack the conserved motifs due to partial sequence. UTRs/CDS along with intronic regions are also represented.
Fig 11
Fig 11. Physicochemical properties of OBPs and ORs.
Molecular weight and isoelectric point of the OBPs and ORs are shown as these are important indicators of the OBPs and ORs functions. Atypical OBPs had highest molecular weight among other classes whereas ORs have higher molecular weight than OBPs.
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