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J. Biol. Chem., Vol. 281, Issue 28, 19172-19178, July 14, 2006

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Phosphatidylethanolamine and Monoglucosyldiacylglycerol Are Interchangeable in Supporting Topogenesis and Function of the Polytopic Membrane Protein Lactose Permease^*

From the Department of Biochemistry and Molecular Biology, University of Texas-Houston, Medical School, and the Graduate School of Biomedical Sciences, Houston, Texas 77030

To determine the specific role lipids play in membrane protein topogenesis in vivo, the orientation with respect to the membrane bilayer of Escherichia coli lactose permease (LacY) transmembrane (TM) domains and their flanking extramembrane domains was compared after assembly in native membranes and membranes with genetically modified lipid content using the substituted cysteine accessibility method for determining TM domain mapping. LacY assembled in the absence of the major membrane lipid phosphatidylethanolamine (PE) does not carry out uphill transport of substrate and displays an inverted orientation for the N-terminal six-TM domain helical bundle (Bogdanov, M., Heacock, P. N., and Dowhan, W. (2002) EMBO J. 21, 2107–2116). Strikingly, the replacement of PE in vivo by the foreign lipid monoglucosyldiacylglycerol (MGlcDAG), synthesized by the Acholeplasma laidlawii MGlcDAG synthase, restored uphill transport and supported the wild type TM topology of the N-terminal helical bundle of LacY. An interchangeable role in defining membrane protein TM domain orientation and supporting function is played by the two most abundant lipids, PE and MGlcDAG, in Gram-negative and Gram-positive bacteria, respectively. Therefore, these structurally diverse lipids endow the membrane with similar properties necessary for the proper organization of protein domains in LacY that are highly sensitive to lipids as topological determinants.

Received for publication, March 20, 2006 , and in revised form, April 27, 2006.

^* This work was supported by Grant R37 GM20478 from the National Institutes of General Medical Sciences (to W. D.) and by a grant from the John S. Dunn, Sr. Research Foundation. 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.

¹ To whom correspondence should be addressed: Dept. of Biochemistry and Molecular Biology, 6431 Fannin St., Suite 6.200, University of Texas-Houston Medical School, Houston, TX 77030. Tel.: 713-500-6051; Fax: 713-500-0562; E-mail: william.dowhan{at}uth.tmc.edu.

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