Arabidopsis mannan synthase CSLA9 and glucan synthase CSLC4 have opposite orientations in the Golgi membrane
Article first published online: 15 NOV 2010
© 2010 The Authors. The Plant Journal © 2010 Blackwell Publishing Ltd
The Plant Journal
Volume 64, Issue 6, pages 1028–1037, December 2010
How to Cite
Davis, J., Brandizzi, F., Liepman, A. H. and Keegstra, K. (2010), Arabidopsis mannan synthase CSLA9 and glucan synthase CSLC4 have opposite orientations in the Golgi membrane. The Plant Journal, 64: 1028–1037. doi: 10.1111/j.1365-313X.2010.04392.x
- Issue published online: 10 DEC 2010
- Article first published online: 15 NOV 2010
- Accepted manuscript online: 5 OCT 2010 03:11PM EST
- Received 19 July 2010; revised 20 September 2010; accepted 30 September 2010; published online 15 November 2010.
- membrane protein topology;
- polysaccharide biosynthesis;
- glycan synthase
Several proteins encoded by the cellulose synthase-like (CSL) gene family are known to be processive glycan synthases involved in the synthesis of cell-wall polysaccharides. These include CSLA proteins, which synthesize β-(14)-linked mannans found in the walls of many plant species, and CSLC proteins, which are thought to synthesize the β-(14)-linked glucan backbone of xyloglucan, an abundant polysaccharide in the primary walls of many plants. CSLA and CSLC proteins are predicted to have multiple membrane spans, and their products (mannan and xyloglucan) accumulate in the Golgi lumen. Knowing where these proteins are located in the cell and how they are orientated in the membrane is important for understanding many aspects of mannan and xyloglucan biosynthesis. In this study, we investigate the subcellular localization and membrane protein topology of CSLA9 and CSLC4, the members of these two families that are most highly expressed in Arabidopsis. CSLA9 and CSLC4 are found predominantly in Golgi membranes, based on co-localization with the known ER/Golgi marker ERD2–YFP. The topology of epitope-tagged proteins was examined using protease protection experiments. Experiments were designed to determine the positions of both the protein termini and the active loop of the CSL proteins investigated. The topology of CSLA9 is characterized by an odd number of transmembrane domains (probably five) and an active site that faces the Golgi lumen. In contrast, CSLC4 has an even number of transmembrane domains (probably six) and an active site that faces the cytosol. The implications of these topologies on various aspects of hemicellulose biosynthesis are discussed.