On the structure of the N-terminal domain of the MscL channel: helical bundle or membrane interface.

Department of Physiology, University of Texas, Southwestern Medical Center at Dallas, Dallas, Texas 75390-9040, USA.
Biophysical Journal (Impact Factor: 3.83). 06/2008; 95(5):2283-91. DOI: 10.1529/biophysj.107.127423
Source: PubMed

ABSTRACT The mechanosensitive channel of large conductance, MscL, serves as a biological emergency release valve protecting bacteria from acute osmotic downshock and is to date the best characterized mechanosensitive channel. A well-recognized and supported model for Escherichia coli MscL gating proposes that the N-terminal 11 amino acids of this protein form a bundle of amphipathic helices in the closed state that functionally serves as a cytoplasmic second gate. However, a recently reexamined crystal structure of a closed state of the Mycobacterium tuberculosis MscL shows these helices running along the cytoplasmic surface of the membrane. Thus, it is unclear if one structural model is correct or if they both reflect valid closed states. Here, we have systematically reevaluated this region utilizing cysteine-scanning, in vivo functional characterization, in vivo SCAM, electrophysiological studies, and disulfide-trapping experiments. The disulfide-trapping pattern and functional studies do not support the helical bundle and second-gate hypothesis but correlate well with the proposed structure for M. tuberculosis MscL. We propose a functional model that is consistent with the collective data.

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    ABSTRACT: Mechanosensitive channels are membrane proteins that open and shut in response to mechanical forces produced by osmotic pressure, sound, touch and gravity. These channels are involved in multiple physiological functions including hypoosmotic pressure, pain, hearing, blood pressure and cell volume regulation. In plants, these channels play a major role in proprioception, gravity sensing and maintenance of plastid shape and size. In the present study, we identified the mechanosensitive channel of small conductance like (MscS) homologue gene family in rice and analyzed their structure, phylogenetic relationship, localization and expression pattern. Five MscS like genes of rice (OsMSL) were found to be distributed on four chromosomes and clustered into two major groups. Subcellular localization predictions of the OsMSL family revealed their localization to plasma membrane, plastid envelope and mitochondria. The predicted gene structure, bonafide conserved signature motif, domain and the presence of transmembrane regions in each OsMSL strongly supported their identity as members of MscS-like gene family. Furthermore, in silico expression analysis of OsMSL genes revealed differential regulation patterns in tissue specific and abiotic stress libraries. These findings indicate that the in silico approach used here successfully identified in a genome-wide context MscS like gene family in rice, and further suggest the functional importance of MscS-like genes in rice.
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May 20, 2014