Article
- The EMBO Journal (2006) 25, 967 - 976
- doi:10.1038/sj.emboj.7601024
Published online: 23 February 2006
Subject Categories:
Two distinct but interchangeable mechanisms for flipping of lipid-linked oligosaccharides
Cristina Alaimo1, Ina Catrein1, Laura Morf1, Cristina L Marolda2, Nico Callewaert3,a, Miguel A Valvano2, Mario F Feldman1 and Markus Aebi1
- Department of Biology, Institute of Microbiology, Swiss Federal Institute of Technology, ETH-Hönggerberg, Zurich, Switzerland
- Department of Microbiology and Immunology, University of Western Ontario, London, ON, Canada
- Zurich Glycomics Initiative, Swiss Federal Institute of Technology, ETH-Hönggerberg, Zurich, Switzerland
Correspondence to:
Markus Aebi, Department of Biology, Institute of Microbiology, Swiss Federal Institute of Technology, ETH Hönggerberg, HCI F407, 8093 Zürich, Switzerland. Tel.: +41 1 632 6413; Fax: +41 1 632 1375; E-mail: aebi@micro.biol.ethz.ch
aPresent address: Unit for Molecular Glycobiology, Department of Molecular Biomedical Research, Ghent University and VIB Technologiepark, 927, 9052 Ghent, Zwijnaarde, Belgium
Received 7 September 2005; Accepted 3 February 2006
Abstract
Translocation of lipid-linked oligosaccharide (LLO) intermediates across membranes is an essential but poorly understood process in eukaryotic and bacterial glycosylation pathways. Membrane proteins defined as translocases or flippases are implicated to mediate the translocation reaction. The membrane protein Wzx has been proposed to mediate the translocation across the plasma membrane of lipopolysaccharide (LPS) O antigen subunits, which are assembled on an undecaprenyl pyrophosphate lipid carrier. Similarly, PglK (formerly WlaB) is a Campylobacter jejuni-encoded ABC-type transporter proposed to mediate the translocation of the undecaprenylpyrophosphate-linked heptasaccharide intermediate involved in the recently identified bacterial N-linked protein glycosylation pathway. A combination of genetic and carbohydrate structural analyses defined and characterized flippase activities in the C. jejuni N-linked protein glycosylation and the Escherichia coli LPS O antigen biosynthesis. PglK displayed relaxed substrate specificity with respect to the oligosaccharide structure of the LLO intermediate and complemented a wzx deficiency in E. coli O-antigen biosynthesis. Our experiments provide strong genetic evidence that LLO translocation across membranes can be catalyzed by two distinct proteins that do not share any sequence similarity.
Keywords:
- ABC transporter,
- flippase,
- N-linked glycosylation,
- O antigen
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