Kira Veley, Grigory Maksaev, Margaret Wilson, Gregory Jensen, Eric Hamilton and Elizabeth S. Haswell*
Department of Biology, Washington University in Saint Louis, USA
*e-mail: ehaswell@wustl.edu
A long-standing problem is how biological systems sense and perceive mechanical signals such as osmotic pressure, gravity, and touch. One well-established molecular mechanism for force sensing is the activation of mechanosensitive (MS) ion channels. The Mechanosensitive channel of Small conductance (MscS) from E. coli functions as a hypo-osmotic safety valve, opening in response to increased membrane tension and preventing cellular rupture. Genes predicted to encode MscS homologs are found in genomes from all three kingdoms of life. We have been characterizing the structure, function, and regulation of ten MscS-Like (MSL) proteins in the model plant Arabidopsis thaliana. Based on their modest homology to MscS and high topological diversity, we have proposed that MSLs might (1) sense and respond to sources of membrane tension other than environmental hypo-osmotic stress; (2) be regulated by mechanisms in addition to membrane tension; and (3) signal in ways that are separable from ion flux. Evidence in support of all three of these hypotheses will be presented.
Left, monomer topology of E. coli MscS. Middle and right, predicted monomer topologies of MSL2 and MSL8, MscS homologs from Arabidopsis thaliana that are localized to the chloroplast and the plasma membrane, respectively.