Mechanosensitive Channel of Small Conductance: More Than Just a Pretty Protein

Cartoon representation on black background colored by chain

Mechanosensitive channel proteins don’t always get the respect that they deserve. It’s easy to forget about our membrane-bound friends, but I want to bring them back into the spotlight.  First of all, their structure is incredible. Mechanosensitive channels form a cylindrical shape made up seven amino acid chains. The structure of mechanosensitive channels is separated into transmembrane and extramembrane regions. Several arginines are located within the transmembrane channel which causes the channel to be positively charged. The positive charge spanning the channel could explain why the mechanosensitive channels prefer to conduct anions rather than cations.

Spheres on white background colored by chainbows

But mechanosensitive channels of small conductance are known for more than just their good looks.  Mechanosensitive channels are important in their role in helping cells adapt to changes in external osmolarity. Applied tension in the cell membrane results in a change in orientation of certain helices which leads to a change in cross sectional area. The channel opens and tension in the cell membrane is relieved. Mechanosensitive channels are also influenced by membrane depolarization and are more likely to be found “open” under such conditions. Loss of function of mechanosensitive channels can be dangerous to an organism. In one study, researchers studied the effects of a peptide found in the venom of tarantulas. The ampiphathic peptide was able to penetrate into the plasma membrane near to the mechanosensitive channel where it then acted as a gating modifier. As mentioned previously, normally during channel opening the protein undergoes a conformational change in which it thins as it widens with the surrounding lipids in the membrane thinning as well. If the tarantula venom peptide is present nearby to the protein channel, it disturbs this process and the channel remains closed.  General anesthesia is also thought to work in a similar way to this. Researchers found that some anesthetics appear to act by incorporating themselves into the plasma membrane. This results in a change in tension in the membrane which leads to a corresponding change in the conformation of the channel protein. An anesthetic will inhibit the channel protein if the conformational change results in a greater cross sectional area in the portion nearest to the aqueous side than the area in the middle of the membrane. However, if the conformational change results in a greater cross sectional area of the channel protein in the middle of the plasma membrane then the anesthetic is going to increase the channel protein’s activity.

Spheres on black background colored by chain

References:

Bass, Randall B., Pavel Strop, Margaret Barclay, and Douglas C. Rees. "Crystal Structure of Escherichia coli MscS, a Voltage-Modulated and Mechanosensitive Channel." Science 298.5598 Nov. (2002): 1582-87.

Hurst, AC, PA Gottlieb, and B Martinac. "Concentration dependent effect of GsMTx4 on mechanosensitive channels of small conductance in E. coli spheroplasts." European Biophysics Journal 38.4 Apr. (2009): 415-25.

Cantor, Robert S. "The Lateral Pressure Profile in Membranes: A Physical Mechanism of General Anesthesia." Biochemistry36.94 Mar. (1997): 2339-44.

Steinbacher, S., R. Bass, P. Strop, and D.C. Rees. "Structures of the Prokaryotic Maechanosensitive Channels MscS." Current Topics in Membranes 58 (2007): 1-24.