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J. Biol. Chem., Vol. 282, Issue 48, 35046-35055, November 30, 2007

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Probing the Structure of the Dimeric KtrB Membrane Protein^*

From the Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520

The KtrAB ion transporter is a complex of two proteins, KtrB and KtrA. The integral membrane protein KtrB is expected to adopt the structural architecture typified by the pore domain of potassium channels. Here we show that homo-dimerization of KtrB proteins is most likely a general property of this family of transporters. Using cysteine mutants and bifunctional cross-linkers we define regions of the Bacillus subtilis KtrB molecule that are close to the molecular 2-fold axis and to the dimer interface. Fitting of the cross-linking data to a potassium channel-like model suggests structural similarities between potassium channels and KtrB proteins in the extracellular half of the molecule and differences in the cytoplasmic regions.

Received for publication, May 23, 2007 , and in revised form, October 9, 2007.

^* This work was supported by the Hellman Family Foundation and National Institutes of Health Grant GM 068585 (to J. H. M.-C.). 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 Fig. S1.

¹ To whom correspondence should be addressed (present address): Instituto de Biologia Molecular e Celular, R. do Campo Alegre, 823, Porto 4150-180, Portugal. Tel.: 351-22-6074-900; Fax: 351-22-6099-157; E-mail: jcabral{at}ibmc.up.pt.

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