Ramya Gamini, Marcos Sotomayor, Christophe Chipot, and Klaus Schulten.
Cytoplasmic domain filter function in the mechanosensitive channel of
small conductance.
Biophysical Journal, 101:80-89, 2011.
(PMC: 3127185)
GAMI2011
Mechanosensitive (MS) channels, inner membrane proteins of bacteria, open and close in response to mechanical stimuli such as changes in membrane tension during osmotic stress. In bacteria, these channels act as safety valves preventing cell lysis upon hypoosmotic cell swelling: the channels open under membrane tension to release
osmolytes along with water. The MS channel of small conductance, MscS, consists, beside the transmembrane channel, of a large cytoplasmic domain (CD) that features a balloon-like, water filled chamber opening to the cytoplasm through seven side pores and a small
distal pore. The CD is apparently a molecular sieve covering the channel, that optimizes loss of osmolytes during osmoadaptation. We employ diffusion theory and molecular dynamics simulations to explore the transport kinetics of Glu and K as representative osmolytes. We suggest that the CD indeed acts as a filter that actually balances passage of Glu and K, and possibly other positive and negative osmolytes, to yield a largely neutral efflux and, thereby, reduce cell depolarization in the open state and conserve to a large degree the essential metabolite Glu.
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