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The Characterization and Structure of Mechanosensitive Channels of Small Conductance


Poon, Yan Shuen (2008) The Characterization and Structure of Mechanosensitive Channels of Small Conductance. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/EBZ2-5D39.


This thesis describes the investigation of the mechanosensitive channel of small conductance (MscS). The Escherichia coli MscS structure shows a homoheptameric ion channel with each monomer consisting of 3 transmembrane (TM) helices leading into the cytoplasmic domain. TM3 from each of the 7 subunits form the pore that opens up into a cytoplasmic cage, thought to be a molecular sieve. In order to further knowledge regarding the mechanism behind bacterial mechanosensation, several approaches were employed. Homologs from organisms indigenous to environments with temperatures ranging from 30°C to 95°C were cloned, expressed, and characterized. Chimeras were constructed between MscS homologs from 6 hyperthermophilic organisms and E. coli MscS, exchanging the transmembrane and cytoplasmic domains. Each protein is engineered with an N-terminal His6 tag and a C-terminal FLAG epitope. 4 homologs were found to be cytotoxic while 3 chimeras failed to rescue the osmotic-shock sensitivity of an E. coli mutant strain lacking endogenous mechanosensitive ion channel activity.

Studies revolving around the various homologs and chimeras led to the crystallization of the Helicobacter pylori MscS homolog. H. pylori MscS shares approximately 35% in sequence identity and was crystallized in space group P212121 with cell dimensions a = 123.0 A, b = 147.4 A, c = 179.4 A. Diffraction data was collected at the Stanford Synchrotron Radiation Laboratory at beamline 12-2 to 4.75 A resolution. A molecular replacement solution was achieved using the program PHASER with the E. coli MscS model (PDB: 2OAU). The refined structure shows a similar overall topology with E. coli MscS demonstrating a homoheptameric channel. The cytoplasmic domain maintains the same structure while TM1 and TM2 display slightly tighter packing with the pore. The structure of the pore suggests that H. pylori and E. coli MscS are crystallized in the same state.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:bacterial; crystal structure; mechanosensitive channel; pore
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Rees, Douglas C.
Thesis Committee:
  • Mayo, Stephen L. (chair)
  • Chan, David C.
  • Rees, Douglas C.
  • Beauchamp, Jesse L.
Defense Date:23 May 2008
Record Number:CaltechETD:etd-05292008-144531
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2262
Deposited By: Imported from ETD-db
Deposited On:02 Jun 2008
Last Modified:18 Dec 2019 22:23

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