s of mechanosensory mechanisms are limited. The mechanosensitive channel of the large conductance (MscL) of E. coli, the first isolated molecule shown to respond to membrane stretch by opening a large aqueous pore, currently is the most accessible model system. The 0.5 kb gene, the purified protein completely functional when reconstituted in lipid bilayers, a variety of mutants, twenty natural homologs, and, finally, the crystal structure of one homolog are now available. This basic project is aimed at detailed functional characterization of MscL and particularly its homolog from M. tuberculosis (Tb-MscL) recently resolved by X-ray crystallography to 3.5 Angstroms in its closed conformation. It appears that it will be difficult to crystallize the native open channel since the energy of the open state is about 19 kbT above the closed state. The long-term goal of the proposed work is to predict the open conformation and understand the opening process.
The specific aims are: (1)To measure the electrophysiological properties of Tb-MscL. (2) Use these results to set constraints for molecular models of the open and subconductance states. The constraints will be obtained from conductances, sieving measurements using polymers, ionic selectivity of the substates and estimates of the changes of in-plane channel expansion associated with the tension dependence of opening. (3) Using effects of co-solvents and site directed mutagenesis to study the nature of intramolecular interactions and role of specific protein motifs that may determine the stretch-sensitivity of MscL. (4) Evaluate energetics of MscL gating in bilayers of different thickness. (5) Evaluate MscL sensitivity to tension in the two monolayers that compose a bilayer since the channel is asymmetric across the bilayer. This will be done by evaluating the gating parameters in conventional 'uncoupled' and 'coupled' bilayers made of archaeal bipolar lipids, and under conditions of a symmetrical bilayer modification. Preliminary computer models of the proteins 3-dimensional structure in open, closed and intermediate conformations have been developed. Testing the critical predictions of these models should clarify the functional role and relationships between different protein domains, and the mechanism by which tension is conveyed from the lipid bilayer to channel gating.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
1R01NS039314-01
Application #
6027309
Study Section
Special Emphasis Panel (ZRG1-MDCN-3 (01))
Program Officer
Talley, Edmund M
Project Start
2000-02-29
Project End
2004-01-31
Budget Start
2000-02-29
Budget End
2001-01-31
Support Year
1
Fiscal Year
2000
Total Cost
$254,626
Indirect Cost
Name
University of Maryland College Park
Department
Biology
Type
Schools of Earth Sciences/Natur
DUNS #
City
College Park
State
MD
Country
United States
Zip Code
20742
Sukharev, Sergei; Sachs, Frederick (2012) Molecular force transduction by ion channels: diversity and unifying principles. J Cell Sci 125:3075-83
Kung, Ching; Martinac, Boris; Sukharev, Sergei (2010) Mechanosensitive channels in microbes. Annu Rev Microbiol 64:313-29
Anishkin, Andriy; Chiang, Chien-Sung; Sukharev, Sergei (2005) Gain-of-function mutations reveal expanded intermediate states and a sequential action of two gates in MscL. J Gen Physiol 125:155-70
Chiang, Chien-Sung; Anishkin, Andriy; Sukharev, Sergei (2004) Gating of the large mechanosensitive channel in situ: estimation of the spatial scale of the transition from channel population responses. Biophys J 86:2846-61
Sukharev, Sergei; Corey, David P (2004) Mechanosensitive channels: multiplicity of families and gating paradigms. Sci STKE 2004:re4
Anishkin, Andriy; Gendel, Vyacheslav; Sharifi, Neda A et al. (2003) On the conformation of the COOH-terminal domain of the large mechanosensitive channel MscL. J Gen Physiol 121:227-44
Sukharev, Sergei (2002) Purification of the small mechanosensitive channel of Escherichia coli (MscS): the subunit structure, conduction, and gating characteristics in liposomes. Biophys J 83:290-8
Sukharev, S; Durell, S R; Guy, H R (2001) Structural models of the MscL gating mechanism. Biophys J 81:917-36