The photoreceptor cell-specific nuclear receptor (PNR), also known as NR2E3 (nuclear receptor subfamily 2, group E, member 3), is a
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
that in humans is encoded by the ''NR2E3''
gene
In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
.
PNR is a member of the
nuclear receptor
In the field of molecular biology, nuclear receptors are a class of proteins responsible for sensing steroids, thyroid hormones, vitamins, and certain other molecules. These intracellular receptors work with other proteins to regulate the ex ...
super family of
intracellular
This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...
transcription factor
In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription (genetics), transcription of genetics, genetic information from DNA to messenger RNA, by binding t ...
s.
Function
PNR is exclusively expressed in the
retina
The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...
. The main target genes of PNR are
rhodopsin
Rhodopsin, also known as visual purple, is a protein encoded by the ''RHO'' gene and a G-protein-coupled receptor (GPCR). It is a light-sensitive receptor protein that triggers visual phototransduction in rod cells. Rhodopsin mediates dim ...
and several
opsin
Animal opsins are G-protein-coupled receptors and a group of proteins made light-sensitive via a chromophore, typically retinal. When bound to retinal, opsins become retinylidene proteins, but are usually still called opsins regardless. Most pro ...
s which are essential for sight.
Structure and ligands
The crystal structure of PNR's ligand-binding domain is known. It self-dimerizes into, by default, a repressor state. Computer simulations based on this model shows that a ligand could possibly fit into PNR and switch it into a transcription activator.
13-cis retinoic acid
Isotretinoin, also known as 13-''cis''-retinoic acid and sold under the brand name Accutane among others, is a medication used to treat skin diseases like harlequin-type ichthyosis, and lamellar ichthyosis, and severe cystic acne or moderat ...
is a known weak agonist that fits into such a pocket, but no physiologic ligand is known. Two synthetic compounds, 11A and 11B, appear to be agonists but do not go into the pocket and instead work as
allosteric modulator
In pharmacology and biochemistry, allosteric modulators are a group of substances that bind to a receptor to change that receptor's response to stimuli. Some of them, like benzodiazepines or alcohol, function as psychoactive drugs. The site that a ...
s.
A more recent screening identifies another compound called photoregulin-1 (PR1) that functions as a reverse agonist, an activity possibly useful in the management of retinitis pigmentosa.
Clinical significance
Mutations in the ''NR2E3'' gene have been linked to several inherited retinal diseases, including enhanced S-cone syndrome (ESCS),
a form of
retinitis pigmentosa
Retinitis pigmentosa (RP) is a member of a group of genetic disorders called inherited retinal dystrophy (IRD) that cause loss of vision. Symptoms include trouble seeing at night and decreasing peripheral vision (side and upper or lower visua ...
,
and Goldmann-Favre syndrome.
References
Further reading
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
External links
*
*
*
*
Intracellular receptors
Transcription factors
Long stubs with short prose
{{gene-15-stub