Structural Basis for the Interaction between Pectin Methylesterase and a Specific Inhibitor Protein

Department of Biochemical Sciences, University of Rome, 00185 Rome, Italy.
The Plant Cell (Impact Factor: 9.34). 04/2005; 17(3):849-58. DOI: 10.1105/tpc.104.028886
Source: PubMed


Pectin, one of the main components of the plant cell wall, is secreted in a highly methyl-esterified form and subsequently deesterified in muro by pectin methylesterases (PMEs). In many developmental processes, PMEs are regulated by either differential expression or posttranslational control by protein inhibitors (PMEIs). PMEIs are typically active against plant PMEs and ineffective against microbial enzymes. Here, we describe the three-dimensional structure of the complex between the most abundant PME isoform from tomato fruit (Lycopersicon esculentum) and PMEI from kiwi (Actinidia deliciosa) at 1.9-A resolution. The enzyme folds into a right-handed parallel beta-helical structure typical of pectic enzymes. The inhibitor is almost all helical, with four long alpha-helices aligned in an antiparallel manner in a classical up-and-down four-helical bundle. The two proteins form a stoichiometric 1:1 complex in which the inhibitor covers the shallow cleft of the enzyme where the putative active site is located. The four-helix bundle of the inhibitor packs roughly perpendicular to the main axis of the parallel beta-helix of PME, and three helices of the bundle interact with the enzyme. The interaction interface displays a polar character, typical of nonobligate complexes formed by soluble proteins. The structure of the complex gives an insight into the specificity of the inhibitor toward plant PMEs and the mechanism of regulation of these enzymes.

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Available from: Giulia De Lorenzo, Apr 15, 2014
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    • "For example, a pepper PMEI can inhibit Arabidopsis PMEs (An et al. 2008), and Arabidopsis and kiwi PMEIs inhibit tomato PMEs (Hothorn et al. 2004). The three-dimensional structure of Arabidopsis and kiwi PMEIs interacting with purified PMEs from tomatoes has been resolved, revealing that PMEI prevents access for the substrate by covering the PME catalytic cleft (Hothorn et al. 2004; Di Matteo et al. 2005). "
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    • "However, to our knowledge, this is the first time a putative PMEI has been identified in border cells. PMEI and PME form a complex in a 1:1 stoichiometric ratio (Di Matteo et al., 2005). Therefore, PMEI expression in border cells appears to be a negative regulator of PME activity and associated with border cell detachment. "
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    • "In bacterial and fungal pathogens, they are involved in maceration and soft-rotting of plant tissue during infections (Lionetti et al. 2012). PMEs are regulated by numerous factors, including pH, cationic concentration, extent of pectin methylesterification, and specific proteinaceous inhibitors of PME activity (PMEI, Micheli 2001; Giovane et al. 2004; Di Matteo et al. 2005; Jolie et al. 2010). In plants, a multigenic family encodes several PME isoforms differing by molecular weight, isoelectric point, and biochemical activity. "
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