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J. Biol. Chem., Vol. 282, Issue 38, 27666-27677, September 21, 2007

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Osmosensing Properties of the Histidine Protein Kinase MtrB from Corynebacterium glutamicum^*

From the Institut für Biochemie der Universität zu Köln, Zülpicher Strasse 47, 50674 Köln, Germany

The MtrB-MtrA two component system of Corynebacterium glutamicum was recently shown to be in involved in the osmostress response as well as cell wall metabolism. To address the question of whether the histidine protein kinase MtrB is an osmosensor, the kinase was purified and reconstituted into liposomes in a functionally active form. The activity regulation was investigated by varying systematically physicochemical parameters, which are putative stimuli that could be used by the bacterial cell to detect osmotic conditions. Membrane shrinkage was ruled out as a stimulus for activation of MtrB. Instead, MtrB was shown to be activated upon the addition of various chemical compounds, like sugars, amino acids, and polyethylene glycols. Because of the different chemical nature of the solutes, it seems unlikely that they bind to a specific binding site. Instead, they are proposed to act via a change of the hydration state of the protein shifting MtrB into the active state. For MtrB activation it was essential that these solutes were added at the same side as the cytoplasmic domains of the kinase were located, indicating that hypertonicity is sensed by MtrB via cytoplasmatically located protein domains. This was confirmed by the analysis of two MtrB mutants in which either the large periplasmic loop or the HAMP domain was deleted. These mutants were regulated similar to wild type MtrB. Thus, we postulate that MtrB belongs to a class of histidine protein kinases that sense environmental changes at cytoplasmatic protein domains independently of the periplasmic loop and the cytoplasmic HAMP domain.

Received for publication, February 28, 2007 , and in revised form, July 20, 2007.

^* This work was supported by Deutsche Forschungsgemeinschaft Grant MO 892/1-1). 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.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1–S4.

¹ To whom correspondence should be addressed. Tel.: 49-221-470-6464; Fax: 49-221-470-5091; E-mail: s.morbach{at}uni-koeln.de.

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