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J. Biol. Chem., Vol. 280, Issue 10, 8784-8792, March 11, 2005

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Lactococcus lactis Uses MscL as Its Principal Mechanosensitive Channel^*

Joost H. A. Folgering, Paul C. Moe¶, Gea K. Schuurman-Wolters, Paul Blount¶, and Bert Poolman||

From the Department of Biochemistry, Groninger Biomolecular Sciences and Biotechnology Institute and Material Science Centre^plus, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands and the Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9040

The functions of the mechanosensitive channels from Lactococcus lactis were determined by biochemical, physiological, and electrophysiological methods. Patch-clamp studies showed that the genes yncB and mscL encode MscS and MscL-like channels, respectively, when expressed in Escherichia coli or if the gene products were purified and reconstituted in proteoliposomes. However, unless yncB was expressed in trans, wild type membranes of L. lactis displayed only MscL activity. Membranes prepared from an mscL disruption mutant did not show any mechanosensitive channel activity, irrespective of whether the cells had been grown on low or high osmolarity medium. In osmotic downshift assays, wild type cells survived and retained 20% of the glycine betaine internalized under external high salt conditions. On the other hand, the mscL disruption mutant retained 40% of internalized glycine betaine and was significantly compromised in its survival upon osmotic downshifts. The data strongly suggest that L. lactis uses MscL as the main mechanosensitive solute release system to protect the cells under conditions of osmotic downshift.

Received for publication, October 15, 2004 , and in revised form, December 20, 2004.

^* This work was supported in part by the Material Science Centre^plus and by Netherlands Organization for Scientific Research Grant R88-247. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

^¶ Supported by National Institutes of Health Grants GM61028 and DK60818, Welch Foundation Grant I-1420, and Air Force Office of Scientific Review Grant F49620-01-1-0503.

^|| To whom correspondence should be addressed. Tel.: 31-50-3634190; Fax: 31-50-3634165; E-mail: B.Poolman{at}rug.nl.

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