In silico characterisation and chromosomal localisation of human RRH (peropsin)--implications for opsin evolution.
BACKGROUND
The vertebrate opsins are proteins which utilise a retinaldehyde chromophore in their photosensory or photoisomerase roles in the visual/irradiance detection cycle. The majority of the opsins, such as rod and cone opsins, have a very highly conserved gene structure suggesting a common lineage. Exceptions to this are RGR-opsin and melanopsin, whose genes have very different intron insertion positions. The gene structure of another opsin, peropsin (retinal pigment epithelium-derived rhodopsin homologue, RRH) is unknown.


RESULTS
By in silico analysis of the GenBank database we have determined that the human RRH comprises 7 exons spanning approximately 16.5 kb and is localised to chromosome 4q25 in the following gene sequence: cen-EGF-RRH-IF-qter - a position that excludes this gene as a candidate for the RP29 autosomal recessive retinitis pigmentosa locus. A comparison of opsin gene structures reveals that RRH and RGR share two common intron (introns 1 and 4) insertion positions which may reflect a shared ancestral gene.


CONCLUSIONS
The opsins comprise a diverse group of genes which appear to have arisen from three different lineages. These lineages comprise the "classical opsin superfamily" which includes the rod and cone opsins, pinopsin, VA-opsin, parapinopsin and encephalopsin; the RRH and RGR group; and the melanopsin line. A common lineage for RRH and RGR, together with their sites of expression in the RPE, indicates that peropsin may act as a retinal isomerase.
Bellingham
James
J
Gene Targeting Unit, Department of Neuromuscular Diseases, Division of Neuroscience and Psychological Medicine, Faculty of Medicine, Imperial College London, Charing Cross Hospital, St. Dunstan's Road, London, W6 8RP, UK. j.bellingham@imperial.ac.uk
Wells
Dominic J
DJ
Foster
Russell G
RG
D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D001483:Base Sequence / Q000235:genetics; D002347:Carps / Q000235:genetics; D002645:Chickens / Q000235:genetics; D002874:Chromosome Mapping / Q000379:methods; D002894:Chromosomes, Human, Pair 4 / Q000235:genetics*; D019295:Computational Biology / Q000379:methods; D030541:Databases, Genetic; D019143:Evolution, Molecular; D005136:Eye Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D010857:Pigment Epithelium of Eye / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics; D043562:Receptors, G-Protein-Coupled; D012243:Rhodopsin; D017299:Rod Opsins / Q000235:genetics*
D005136:Eye Proteins; C089754:G protein-coupled receptor RGR; C504671:RRH protein, human; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D017299:Rod Opsins; D012243:Rhodopsin