Glutamate receptor, metabotropic 6, also known as GRM6 or mGluR6, is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

which in humans is encoded by the ''GRM6''

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

Function

L-

glutamate Glutamic acid (symbol Glu or E; the ionic form is known as glutamate) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can syn ...

is the major excitatory

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell. Neuro ...

in the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...

and activates both ionotropic and metabotropic glutamate receptors. Glutamatergic neurotransmission is involved in most aspects of normal brain function and can be perturbed in many neuropathologic conditions. The

metabotropic glutamate receptor The metabotropic glutamate receptors, or mGluRs, are a type of glutamate receptor that are active through an indirect metabotropic process. They are members of the group C family of G-protein-coupled receptors, or GPCRs. Like all glutamate rece ...

s are a family of

G protein-coupled receptor G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of evolutionarily-related p ...

s, that have been divided into 3 groups on the basis of sequence homology, putative signal transduction mechanisms, and pharmacologic properties. Group I includes

GRM1 The glutamate receptor, metabotropic 1, also known as GRM1, is a human gene which encodes the metabotropic glutamate receptor 1 (mGluR1) protein. Function L-glutamate is the major excitatory neurotransmitter in the central nervous system and ...

and

GRM5 Metabotropic glutamate receptor 5 is an excitatory Gq-coupled G protein-coupled receptor predominantly expressed on the postsynaptic sites of neurons. In humans, it is encoded by the ''GRM5'' gene. Function The amino acid L-glutamate is the m ...

and these receptors have been shown to activate

phospholipase C Phospholipase C (PLC) is a class of membrane-associated enzymes that cleave phospholipids just before the phosphate group (see figure). It is most commonly taken to be synonymous with the human forms of this enzyme, which play an important role ...

. Group II includes

GRM2 Metabotropic glutamate receptor 2 (mGluR2) is a protein that, in humans, is encoded by the ''GRM2'' gene. mGluR2 is a G protein-coupled receptor (GPCR) that couples with the Gi alpha subunit. The receptor functions as an autoreceptor for glutam ...

and

GRM3 Metabotropic glutamate receptor 3 (mGluR3) is an inhibitory Gi/G0-coupled G-protein coupled receptor (GPCR) generally localized to presynaptic sites of neurons in classical circuits. However, in higher cortical circuits in primates, mGluR3 are lo ...

, while Group III includes

GRM4 Metabotropic glutamate receptor 4 is a protein that in humans is encoded by the ''GRM4'' gene. Together with GRM6, GRM7 and GRM8 it belongs to group III of the metabotropic glutamate receptor family. Group III receptors are linked to the inhibi ...

, GRM6,

GRM7 Metabotropic glutamate receptor 7 is a protein that in humans is encoded by the ''GRM7'' gene. Function L-glutamate is the major excitatory neurotransmitter in the central nervous system and activates both ionotropic and metabotropic glutam ...

and

GRM8 Metabotropic glutamate receptor 8 is a protein that in humans is encoded by the ''GRM8'' gene. Function L-glutamate is the major excitatory neurotransmitter in the central nervous system and activates both ionotropic and metabotropic glutam ...

. Group II and III receptors are linked to the inhibition of the

cyclic AMP Cyclic adenosine monophosphate (cAMP, cyclic AMP, or 3',5'-cyclic adenosine monophosphate) is a second messenger important in many biological processes. cAMP is a derivative of adenosine triphosphate (ATP) and used for intracellular signal transd ...

cascade but differ in their agonist selectivities. mGluR6 is specifically expressed in the retina, in a subtype of bipolar cells that depolarize in response to light, known as ON bipolar cells. These cells form

synapses In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell. Synapses are essential to the transmission of nervous impulses from ...

with photoreceptor cells, and detect the

glutamate via a GPCR signal transduction cascade. The glutamate receptor mGluR6 is located post-synaptically at the tips of the bipolar cell

dendrites Dendrites (from Greek δένδρον ''déndron'', "tree"), also dendrons, are branched protoplasmic extensions of a nerve cell that propagate the electrochemical stimulation received from other neural cells to the cell body, or soma, of the n ...

, and is responsible for initiating a signaling cascade that ultimately controls gating of the

TRPM1 Transient receptor potential cation channel subfamily M member 1 is a protein that in humans is encoded by the ''TRPM1'' gene. Function The protein encoded by this gene is a member of the transient receptor potential (TRP) family of non-select ...

channel. In human patients, mutations in the ''GRM6'' gene are associated with

congenital stationary night blindness Congenital stationary night blindness (CSNB) is a rare non-progressive retinal disorder. People with CSNB often have difficulty adapting to low light situations due to impaired photoreceptor transmission. These patients may also have reduced visua ...

Function

See also

References

Further reading