What is TRPM
TRPM is a family of transient receptor potential ion channels where the “M” stands for “melastatin”.[1] Functional TRPM channels are believed to form tetramers.[2]
Unlike the TRPC and TRPV sub-families, TRPM subunits do not contain N-terminal ankyrin repeat motifs but, rather, contain entire functional proteins in their C-termini. TRPM6 and TRPM7, for example, contain functional ?-kinase segments, which are a type of serine/threonine-specific protein kinase.
Tags: Integral membrane proteins, Ion channels, Membrane proteins, Proteins, Transmembrane proteins
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The relative permeability of calcium and magnesium varies widely among TRPM channels.
TRPM4/5 are impermeable to calcium.
TRPM3/6/7 are highly permeable to both calcium and magnesium.
The mechanism of activation also varies greatly among TRPM channels.
TRPM2 is activated by ADP-ribose Adenosine 5'-diphosphoribose and functions as a sensor of redox status in cells.[3]
TRPM4/5 are activated by intracellular calcium.
TRPM8, conversely, can be activated by low temperatures, menthol, eucalyptol and icilin.
Among the functional responsibilities of the TRPM channels are:
regulation of calcium oscillations after T cell activation (TRPM4).[6]
sensory transduction in taste cells (TRPM5).
regulation of magnesium reabsorption in the kidneys and absorption in the intestines (TRPM6).[7]
regulation of cell adhesion (TRPM7).
The investigation of the TRPM genes and proteins in human cells is an area of intense recent study and, at times, debate. Montell et al. (2002)[72] have reviewed the research into the TRP genes, and a second review by Montell (2003)[73] has reviewed the research into the TRPM genes.
The TRPM family of ion channels has members throughout the metazoa. The TRPM6 and TRPM7 proteins are highly unusual, containing both an ion channel domain and a kinase domain (Figure 1.7). The role of the kinase domain brings about the most heated debate[73].
The activity of these two proteins has been very difficult
There are other types of ion channel classifications that are based on less normal characteristics, e.g. multiple pores and transient potentials.
Almost all ion channels have one single pore. However, there are also those with two:
Two-pore channels: This small family of 2 members putatively forms cation-selective ion channels. They are predicted to contain two KV-style six-transmembrane domains, suggesting they form a dimer in the membrane. These channels are related to catsper channels channels and, more distantly, TRP channels.
There are channels that are classified by the duration of the response to stimuli:
Transient receptor potential channels: This group of channels, normally referred to
Voltage-gated channels open and close in response to membrane potential.
Voltage-gated sodium channels: This family contains at least 9 members and is largely responsible for action potential creation and propagation. The pore-forming ? subunits are very large (up to 4,000 amino acids) and consist of four homologous repeat domains (I-IV) each comprising six transmembrane segments (S1-S6) for a total of 24 transmembrane segments. The members of this family also coassemble with auxiliary ? subunits, each spanning the membrane once. Both ? and ? subunits are extensively glycosylated.
Voltage-gated calcium channels: This family contains 10 members, though these members are known to coassemble
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