Nematode chemoreceptors are chemoreceptors of

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...

s. Animals recognise a wide variety of chemicals using their senses of taste and smell. The nematode ''

Caenorhabditis elegans ''Caenorhabditis elegans'' () is a free-living transparent nematode about 1 mm in length that lives in temperate soil environments. It is the type species of its genus. The name is a blend of the Greek ''caeno-'' (recent), ''rhabditis'' (ro ...

'' has only 14 types of chemosensory neuron, yet is able to respond to dozens of chemicals because each neuron detects several stimuli. More than 40 highly divergent transmembrane proteins that could contribute to this functional diversity have been described. Most of the candidate receptor genes are in clusters of similar genes; 11 of these appear to be expressed in small subsets of chemosensory neurons. A single type of neuron can potentially express at least 4 different receptor genes. Some of these might encode receptors for water-soluble attractants, repellents and pheromones, which are divergent members of the G-protein-coupled receptor family. Sequences of the Sra family of ''C. elegans'' receptor-like proteins contain 6-7 hydrophobic, putative transmembrane, regions. These can be distinguished from other 7TM proteins (especially those known to couple G-proteins) by their own characteristic TM signatures. More than 1300 potential chemoreceptor genes have been identified in ''C. elegans'', which are generally prefixed sr for

serpentine Serpentine may refer to: Shapes * Serpentine shape, a shape resembling a serpent * Serpentine curve, a mathematical curve * Serpentine, a type of riding figure Science and nature * Serpentine subgroup, a group of minerals * Serpentinite, a ...

receptor. The receptor superfamilies include Sra (Sra, Srb, Srab, Sre), Str (Srh, Str, Sri, Srd, Srj, Srm, Srn) and Srg (Srx, Srt, Srg, Sru, Srv, Srxa), as well as the families Srw, Srz, Srbc, Srsx and Srr. Many of these proteins have homologues in '' Caenorhabditis briggsae''. These receptors are distantly related to the

rhodopsin-like receptors Rhodopsin-like receptors are a family of proteins that comprise the largest group of G protein-coupled receptors. Scope G-protein-coupled receptors, GPCRs, constitute a vast protein family that encompasses a wide range of functions (including ...

. In contrast the receptor Sro is a true rhodopsin-like receptor. It is a member of the nemopsins a subgroup of the opsins, but unlike most other opsins it does not have a lysine corresponding to position 296 in cattle

rhodopsin Rhodopsin, also known as visual purple, is a protein encoded by the RHO gene and a G-protein-coupled receptor (GPCR). It is the opsin of the rod cells in the retina and a light-sensitive receptor protein that triggers visual phototransduction ...

. The lysine is replaced by an asparagine. The lysine is needed so that the

chromophore A chromophore is the part of a molecule responsible for its color. The color that is seen by our eyes is the one not absorbed by the reflecting object within a certain wavelength spectrum of visible light. The chromophore is a region in the molec ...

retinal can covalently bind to the opsin via a Schiff-base, which makes the opsin light sensitive. If the lysine is replaced by another amino acid then the opsin becomes light insensitive. Therefore, Sro is also thought to be a chemoreceptor.

References

G protein-coupled receptors Chemoreceptor {{membrane-protein-stub