Mechanosensitive ion channel
Mechanosensitive channels (MS channels) are found in a number of tissues and organisms and are thought to be the sensors for a number of systems including the senses of touch, hearing and balance, as well as participating in cardiovascular regulation and osmotic homeostasis (e.g. thirst). They are present in the membranes of organisms from the three domains of life: bacteria, archaea, and eukarya.[1]. Mechanosensitive channels were first observed in chick skeletal muscles by Falguni Guharay and Frederick Sachs in 1983 and the results were published in 1984 [2].
For a protein to be considered mechanosensitive, it must respond to a mechanical deformation of the membrane. Mechanical deformations can include changes in the tension, thickness, or curvature of the membrane. Mechanosensitive channels respond to membrane tension by altering their conformation between an open state and a closed state.[3][4] One type of mechanically sensitive ion channel activates specialized sensory cells, such as cochlear hair cells and some touch sensory neurons, in response to forces applied to proteins.[5][6] In eukaryotes, two of the best known mechanosensitive ion channels are the potassium channels TREK-1 and TRAAK, both of which are found in mammalian neurons.
The bacterial MS channels are the best studied, and provide a paradigm of how a protein senses membrane stretch. They are involved in osmotic homeostasis, serving as 'emergency release valves' protecting the cell from acute decreases in osmotic environment. There are two families of bacterial MS channels:
- Large-conductance mechanosensitive channel, MscL
- Small-conductance MS channels (MscS or YggB). The pressure threshold for MscS opening is 50% that of MscL.[7]
The MscS family is much larger and more variable in size and sequence than the MscL family. Much of the diversity in MscS proteins occurs in the size of the transmembrane regions, which ranges from three to eleven transmembrane helices, although the three C-terminal helices are conserved.
MscS folds as a homo-heptamer with a cylindrical shape, and can be divided into transmembrane and extramembrane regions: an N-terminal periplasmic region, a transmembrane region, and a C-terminal cytoplasmic region (middle and C-terminal domains). The transmembrane region forms a channel through the membrane that opens into a chamber enclosed by the extramembrane portion, the latter connecting to the cytoplasm through distinct portals.[7]
References
- ^ Pivetti CD, Yen MR, Miller S; et al. (2003). "Two families of mechanosensitive channel proteins". Microbiol. Mol. Biol. Rev. 67 (1): 66–85, table of contents. doi:10.1128/MMBR.67.1.66-85.2003. PMC 150521. PMID 12626684.
{{cite journal}}: Explicit use of et al. in:|author=(help)CS1 maint: multiple names: authors list (link) - ^ ncbi.nlm.nih.gov/pmc/articles/PMC1193237/pdf/jphysiol00593-0701.pdf,
- ^ Attention: This template ({{cite pmid}}) is deprecated. To cite the publication identified by PMID 7690260, please use {{cite journal}} with
|pmid= 7690260instead. - ^ Attention: This template ({{cite pmid}}) is deprecated. To cite the publication identified by PMID 22000509, please use {{cite journal}} with
|pmid= 22000509instead. - ^ Ernstrom, GG; Chalfie, M (2002). "Genetics of sensory mechanotransduction". Annu. Rev. Genet. 36: 411–453.
- ^ Garcia-Anoveros, J; Corey, D.P. (1996). "Mechanosensation: Touch at the molecular level". Curr. Biol. l6 (5): 541–543.
- ^ a b Bass RB, Strop P, Barclay M, Rees DC (2002). "Crystal structure of Escherichia coli MscS, a voltage-modulated and mechanosensitive channel". Science. 298 (5598): 1582–7. doi:10.1126/science.1077945. PMID 12446901.
{{cite journal}}: CS1 maint: multiple names: authors list (link)