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RRH
Identifiers
Aliases	RRH, retinal pigment epithelium-derived rhodopsin homolog
External IDs	OMIM: 605224; MGI: 1097709; HomoloGene: 55977; GeneCards: RRH; OMA:RRH - orthologs
Gene location (Human) Chr. Chromosome 4 (human) Band 4q25 Start 109,827,972 bp End 109,849,123 bp
Gene location (Mouse) Chr. Chromosome 3 (mouse) Band 3 G3|3 59.09 cM Start 129,598,057 bp End 129,616,236 bp
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in testicle retinal pigment epithelium cerebellar cortex cerebellar hemisphere right hemisphere of cerebellum prefrontal cortex Achilles tendon stromal cell of endometrium Brodmann area 9 developmental structure Top expressed in retinal pigment epithelium neural layer of retina zygote secondary oocyte primary oocyte morula lens ciliary body embryo Epithelium of choroid plexus More reference expression data BioGPS More reference expression data
Gene ontology Molecular function photoreceptor activity signal transducer activity G protein-coupled receptor activity G protein-coupled photoreceptor activity Cellular component integral component of membrane integral component of plasma membrane membrane photoreceptor outer segment Biological process signal transduction response to stimulus visual perception G protein-coupled receptor signaling pathway phototransduction detection of visible light cellular response to light stimulus Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 10692 20132 Ensembl ENSG00000180245 ENSMUSG00000028012 UniProt O14718 O35214 RefSeq (mRNA) NM_006583 NM_009102 RefSeq (protein) NP_006574 NP_033128 Location (UCSC) Chr 4: 109.83 – 109.85 Mb Chr 3: 129.6 – 129.62 Mb PubMed search
Wikidata
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Peropsin, a visual pigment-like receptor, is a protein that in humans is encoded by the RRH gene. It belongs like other animal opsins to the G protein-coupled receptors. Even so, the first peropsins were already discovered in mice and humans in 1997, not much is known about them.

Photochemistry

Like most opsins, peropsins have in its seventh transmembrane domain a lysine corresponding to amino acid position 296 in cattle rhodopsin, which is important for retinal binding and light sensing.

In amphioxus, a cephalochordate, a peropsin binds in the dark-state all-trans-retinal instead of 11-cis-retinal, as it is in cattle rhodopsin. Therefore, peropsins have been suggested to be photoisomerases.

Tissue localization

In mice, a peropsin is localized to the apical microvilli of the retinal pigment epithelium (RPE). There, it regulates storage or the movement of vitamin A from the retina to the RPE. A peropsin is also expressed in keratinocytes of the human skin. In keratinocyte cell culture, it reacts to UV light if retinal is supplied. In chicken, a peropsin is expressed with an RGR-opsin in the pineal gland and the retina.

Gene localization and structure

The human peropsin gene lies on chromosome 4 band 4q25 and has six introns like RGR-opsins. However only two of these introns are inserted at the same place, which still indicates that peropsins and RGR-opsins are more closely related to each other than to the ciliary and rhabdomeric opsins. This shared gene structure is also reflected in opsin phylogenies, where peropsins and RGR-opsins are in the same group: The chromopsins.

Phylogeny

The peropsins are restricted to the craniates and the cephalochordates. The craniates are the taxon that contains mammals and with them humans. The peropsins are one of the seven subgroups of the chromopsins. The other groups are the RGR-opsins, the retinochromes, the nemopsins, the astropsins, the varropsins, and the gluopsins. The chromopsins are one of three subgroups of the tetraopsins (also known as RGR/Go or Group 4 opsins). The other groups are the neuropsins and the Go-opsins. The tetraopsins are one of the five major groups of the animal opsins, also known as type 2 opsins). The other groups are the ciliary opsins (c-opsins, cilopsins), the rhabdomeric opsins (r-opsins, rhabopsins), the xenopsins, and the nessopsins. Four of these subclades occur in Bilateria (all but the nessopsins). However, the bilaterian clades constitute a paraphyletic taxon without the opsins from the cnidarians.

• Phylogenetic reconstruction of the opsins. The outgroup contains other G protein-coupled receptors. The frame highlights the tetraopsins, which are expanded in the next image.
• Phylogenetic reconstruction of the tetraopsins. The outgroup contains other G protein-coupled receptors including the other opsins. The frame highlights the chromopsins, which are expanded in the next image.
• Phylogenetic reconstruction of the chromopsins. The outgroup contains other G protein-coupled receptors including the other opsins. The frame highlights the peropsins.

In the phylogeny above, Each clade contains sequences from opsins and other G protein-coupled receptors. The number of sequences and two pie charts are shown next to the clade. The first pie chart shows the percentage of a certain amino acid at the position in the sequences corresponding to position 296 in cattle rhodopsin. The amino acids are color-coded. The colors are red for lysine (K), purple for glutamic acid (E), orange for arginine (R), dark and mid-gray for other amino acids, and light gray for sequences that have no data at that position. The second pie chart gives the taxon composition for each clade, green stands for craniates, dark green for cephalochordates, mid green for echinoderms, brown for nematodes, pale pink for annelids, dark blue for arthropods, light blue for mollusks, and purple for cnidarians. The branches to the clades have pie charts, which give support values for the branches. The values are from right to left SH-aLRT/aBayes/UFBoot. The branches are considered supported when SH-aLRT ≥ 80%, aBayes ≥ 0.95, and UFBoot ≥ 95%. If a support value is above its threshold the pie chart is black otherwise gray.

Clinical significance

Since RGR-opsin may be associated with retinitis pigmentosa, which is like peropsin also expressed in the retinal pigment epithelium, peropsin was screened for a link with retinitis pigmentosa. However, no link could be established.

References

1. ^ GRCh38: Ensembl release 89: ENSG00000180245 – Ensembl, May 2017
2. ^ GRCm38: Ensembl release 89: ENSMUSG00000028012 – Ensembl, May 2017
3. "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
4. "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
5. ^ Sun H, Gilbert DJ, Copeland NG, Jenkins NA, Nathans J (September 1997). "Peropsin, a novel visual pigment-like protein located in the apical microvilli of the retinal pigment epithelium". Proceedings of the National Academy of Sciences of the United States of America. 94 (18): 9893–9898. Bibcode:1997PNAS...94.9893S. doi:10.1073/pnas.94.18.9893. PMC 23288. PMID 9275222.
6. ^ "Entrez Gene: RRH retinal pigment epithelium-derived rhodopsin homolog".
7. ^ Gühmann M, Porter ML, Bok MJ (August 2022). "The Gluopsins: Opsins without the Retinal Binding Lysine". Cells. 11 (15): 2441. doi:10.3390/cells11152441. PMC 9368030. PMID 35954284. Material was copied and adapted from this source, which is available under a Creative Commons Attribution 4.0 International License.
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This article incorporates text from the United States National Library of Medicine, which is in the public domain.

• Genes on human chromosome 4
• G protein-coupled receptors