Mechanosensitive ion channel
Mycobacterium tuberculosis (bacteria)
Mechanosensitive (MS) ion channels are the transmembrane proteins that primarily sense physical stress exerted on cell membranes. These ion channels have the ability to transduce the mechanical force applied to the cell membrane into an electrochemical response, enabling cells to respond to stimuli such as sound, touch, gravity and pressure. The large-conductance MS channel (MscL) is one well-known MS ion channel, which regulates osmotic pressure changes in cells.
MscL is a homopentamer and each of its five subunits contains two transmembrane alpha helices, TM1 and TM2, and one cytoplasmic alpha helix. The pore through which ions pass is formed in the center of the pentamer, lined with hydrophilic residues. From the entrance at the extracellular side, the pore narrows to an obstructed hydrophobic tip at the cytoplasmic side. The tip formed by the junction of the five TM1, is considered the gate that restricts the permeation of ions through the pore. The structural analysis of MscL has suggested a mechanism for the channel opening and closing in response to mechanical membrane stress. By applying lateral tension to the membrane, the conformation of the transmembrane region of MscL is changed; the TM1 helices are pulled away from each other and inserted between TM2 helices. As a result, the constriction of the central pore is relaxed so that ions can pass through the membrane. Thus, MS ion channels directly convert mechanical stress into conformational changes that allow ions to cross the membrane and elicit an electrochemical response.
Protein Data Bank (PDB)
Chang, G. Spencer, R.H. Lee, A.T. Barclay, M.T. Rees, D.C.; "Structure of the MscL homolog from Mycobacterium tuberculosis: a gated mechanosensitive ion channel."; Science; (1998) 282:2220-2226 PubMed:9856938.
author: Yuko Tsuchiya