Gating-associated conformational changes in the mechanosensitive channel MscL.
Kenjiro Yoshimura1, Jiro Usukura, Masahiro Sokabe
1Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8572, Japan. kenjiro@biol.tsukuba.ac.jp
Summary
Bacterial mechanosensitive channel MscL opens to prevent cell lysis under hypoosmotic shock. Structural analysis reveals pore formation and carboxyl-terminal protrusion dissociation upon MscL opening.
Area of Science:
- Biophysics
- Molecular Biology
- Cell Biology
Background:
- Bacterial cells utilize the mechanosensitive channel MscL to prevent lysis during hypoosmotic stress.
- MscL is believed to expand and form a large pore (3-4 nm diameter) upon opening.
Purpose of the Study:
- To analyze the closed and open structures of cell-free MscL.
- To investigate the structural changes associated with MscL channel gating.
Main Methods:
- Patch-clamp electrophysiology on MscL reconstituted into liposomes.
- Analysis of a constitutively open MscL mutant (G22N MscL).
- Electrophoretic analysis of cross-linked MscL and electron microscopy with low-angle rotary shadowing.
Main Results:
- Wild-type MscL required mechanical stimulation for activation, while G22N MscL showed spontaneous opening.
- G22N MscL exhibited a slower electrophoretic migration, indicating an expanded conformation.
- Electron microscopy revealed a central pore in G22N MscL but not in wild-type MscL, which had a distinct protrusion.
Conclusions:
- MscL opening involves pore formation and the dissociation of a carboxyl-terminal protrusion.
- The G22N mutation stabilizes MscL in an open, expanded state with a pore.
- Structural insights into MscL gating mechanism provide a basis for understanding mechanotransduction in bacteria.
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