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An extra sugar provides protection

NLP proteins constitute a superfamily of proteins produced by plant pathogenic bacteria, fungi, and oomycetes. NLP refers to “Necrosis and ethylene-inducing peptide 1–like proteins”, describing effects of these proteins in target plants, i.e. tissue cell death (necrosis) and production of the plant hormone ethylene, produced in response to environmental stress. Many NLPs are cytotoxins that facilitate microbial infection of eudicot plants (like tomato and tobacco), but not of monocots (like cereals and leek). The molecular basis of such specificity of members of the NLP family of toxins has been revealed for the oomycete plant pathogen Pythium aphanidermatum. Namely, the crystal structures of its cytotoxin NLPPya in complex with two different sugar moieties, complemented with other experimental evidence suggested the authors to consider glycosylinositol phosphorylceramide (GIPC) sphingolipids as NLP toxin receptors, and differences in structures of GIPC receptors between monocots and eudicots to justify the differences in NLP sensitivity. In plants, GIPCs are major constituents of membranes, comprising up to 40% of plasma membrane lipids, reaching up to 60 to 80% of lipids in the outer leaflet of the plasma membrane. A GIPC molecule consists of an inositol phosphoceramide, which stabilizes its position in the membrane, and a head group consisting of glucuronic acid and a variable number and form of terminal hexoses (6-carbon sugars, such as glucosamine or mannosamine). The sugar moiety is positioned at the extracellular surface of the plant cell membrane reaching out of the lipid bilayer and is thus accessible for binding of NLP proteins.

Figure 1. Structural change in NLP protein upon sugar binding.Crystal structures of NLPPyabefore (blue, PDB ID 3GNZ, left) and after glucosamine binding (green, PDB ID 5NNW, right). Mg2+ ion is depicted as a pink sphere, glucosamine as orange sticks.

Different biochemical and biophysical assays confirmed that NLPs bind GIPCs with high affinity, but not other lipids. Because monomeric sugars glucosamine and mannosamine were found to bind to the NLP protein, they were used to determine crystal structures of protein-sugar complexes using the XRD1 beamline at Elettra: sugar binding resulted in structural changes in the NLPPya (Figure 1) resulting in formation of a channel harbouring the sugar, thereby suggesting that NLPs use this opening to anchor themselves to GIPC sugar head groups with a subsequent recruitment of other parts of the NLP molecule. This process proceeds efficiently in dicots, while in monocots additional sugar on GIPC head group leads to more distant placement of NLP on the surface of plant cells and resistance of plants against its activity (Figure 2).

Figure 2Differences in GIPCs head groups between dicots (image bottom) and monocots (top) allow the toxin NLP to be able to reach the surface of plant cells and harm them (bottom) producing nectrosis or not (image top, monocots).
 

This research was conducted by the following research team:

Tea Lenarčič1, Katja Pirc1, Apolonija B. Zavec1, Marjetka Podobnik1, Gregor Anderluh1, Vesna Hodnik2, Isabell Albert3,Hannah Böhm3,Rory Pruitt3, Claudia Oecking3, Thorsten Nürnberger3,David Pahovnik4, Ema Žagar4, Peter Greimel5, Akiko Yamaji-Hasegawa6, Toshihide Kobayashi7, Agnieszka Zienkiewicz8, Jasmin Gömann8, Ivo Feussner8, Jenny C. Mortimer9, Lin Fang9, Adiilah Mamode-Cassim10, Sébastien Mongrand10, Magali Deleu11 and Laurence Lins11


Department for Molecular Biology and Nanobiotechnology, National Institute of Chemistry, Ljubljana, Slovenia
Department for Molecular Biology and Nanobiotechnology, National Institute of Chemistry and Department of Biology, Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia.
Centre of Plant Molecular Biology, Eberhard-Karls-University Tübingen, Tübingen, Germany
Department of Polymer Chemistry and Technology, National Institute of Chemistry, Ljubljana, Slovenia
Lipid Biology Laboratory andLaboratory for Cell Function Dynamics, Brain Science Institute, RIKEN Institute, Wako, Saitama, Japan
Lipid Biology Laboratory and Molecular Membrane Neuroscience, Brain Science Institute, RIKEN Institute, Wako, Saitama, Japan
Lipid Biology Laboratory, RIKEN Institute, Wako Saitama, Japan and UMR 7213 CNRS, University of Strasbourg, Illkirch, France
8 Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences and Göttingen Center for Molecular Biosciences, University of Göttingen, Germany.
Joint Bioenergy Institute, Emeryville and Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, USA
10 Laboratoire de Biogenèse Membranaire, UMR 5200 CNRS-Université de Bordeaux, Villenave-d’Ornon Cedex, France
11 Laboratory of Molecular Biophysics at Interfaces, University of Liège, Gembloux, Belgium


Contact person:

Maurizio Polentarutti, email: maurizio.polentarutti@elettra.eu

 

Reference

T. Lenarčič, I. Albert, H. Böhm, V. Hodnik, K. Pirc, A. B. Zavec, M. Podobnik, D. Pahovnik, E. Žagar, R. Pruitt, P. Greimel, A. Yamaji-Hasegawa, T. Kobayashi, A. Zienkiewicz, J. Gömann, J. C. Mortimer, L. Fang, A. Mamode-Cassim, M. Deleu, L. Lins, C. Oecking, I. Feussner, S. Mongrand, G. Anderluh and T. Nürnberger, "Eudicot plant-specific sphingolipids determine host selectivity of microbial NLP cytolysins", Science 358, 1431 (2017), DOI:10.1126/science.aan6874
 
Last Updated on Tuesday, 30 January 2018 16:30