Stringent in-silico identification of putative G-protein-coupled receptors (GPCRs) of the entomopathogenic nematode Heterorhabditis bacteriophora

The infective juveniles (IJs) of entomopathogenic nematode (EPN) Heterorhabditis bacteriophora find and infect their host insects in heterogeneous soil ecosystems by sensing a universal host cue (CO2) or insect/plant-derived odorants, which bind to various sensory receptors, including G protein-coupled receptors (GPCRs). Nematode chemosensory GPCRs (NemChRs) bind to a diverse set of ligands, including odor molecules. However, there is a lack of information on the NemChRs in EPNs. Here we identified 21 GPCRs in the H. bacteriophora genome sequence in a triphasic manner, combining various transmembrane detectors and GPCR predictors based on different algorithms, and considering inherent properties of GPCRs. The pipeline was validated by reciprocal BLAST, InterProscan, GPCR-CA, and NCBI CDD search. Functional classification of predicted GPCRs using Pfam revealed the presence of four NemChRs. Additionally, GPCRs were classified into various families based on the reciprocal BLAST approach into a frizzled type, a secretin type, and 19 rhodopsin types of GPCRs. Gi/o is the most abundant kind of G-protein, having a coupling specificity to all the fetched GPCRs. As the 21 GPCRs identified are expected to play a crucial role in the host-seeking behavior, these might be targeted to develop novel insect-pest management strategies by tweaking EPN IJ behavior, or to design novel anthelminthic drugs. Our new and stringent GPCR detection pipeline may also be used to identify GPCRs from the genome sequence of other organisms.