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

ABSTRACT 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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    • "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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    ABSTRACT: Integrated metabolomics and transcriptomics of Medicago truncatula seedling border cells and root tips revealed substantial metabolic differences between these distinct and spatially segregated root regions. Large differential increases in oxylipin-pathway lipoxygenases and auxin-responsive transcript levels in border cells corresponded to differences in phytohormone and volatile levels compared to adjacent root tips. Morphological examinations of border cells revealed the presence of significant starch deposits which serve as critical energy and carbon reserves as documented through increased β-amylase transcript levels and associated starch hydrolysis metabolites. A substantial proportion of primary metabolism transcripts were decreased in border cells while many flavonoid- and triterpenoid-related metabolite and transcript levels were dramatically increased. The cumulative data provide compounding evidence that primary and secondary metabolism are differentially programmed in border cells relative to root tips. Metabolic resources normally destined for growth and development are redirected towards elevated accumulation of specialized metabolites in border cells, resulting in constitutively elevated defense and signaling compounds needed to protect the delicate root cap and signal motile rhizobia required for symbiotic nitrogen fixation. Elevated levels of 7,4'-dihydroxyflavone (DHF) were further increased in border cells of roots exposed to Phymatotrichopsis omnivora, and the value of DHF as an antimicrobial compound was demonstrated using in vitro growth inhibition assays. The cumulative and pathway-specific data provide key insights into the metabolic programming of border cells that strongly implicate a more prominent mechanistic role for border cells in plant-microbe signaling, defense and interactions than previously envisioned. Copyright © 2015, American Society of Plant Biologists.
    Plant physiology 02/2015; 167(4). DOI:10.1104/pp.114.253054 · 6.84 Impact Factor
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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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    ABSTRACT: Plant viruses are obligate parasites that exploit host components for replication and spread inside the host. Transport of the viral genome is enabled by movement proteins (MPs) targeting the cell periphery to mediate passage throughout plasmodesmata (PD). Pectin methylesterase (PME) is one of the critical host factors facilitating MPs in PD gating, and a direct interaction of PME with Tobacco mosaic virus (TMV) MP is required for viral movement and in turn for virus viability. PME is a critical enzyme for host development and defence, acting via complex mechanisms involving multigenic and tissue specific isoforms and endogenous inhibitors. This composite activity of PME suggests that level and timing of protein accumulation, with respect to virus inoculation and MP expression, can be critical for the functional outcome of the PME-MP interaction and in turn for the success of a viral infection. Based on this notion, we tested different experimental conditions to evaluate the beneficial effect of the downregulation of PME gene expression on the development of TMVinduced disease and on plant protection. We used virus induced gene silencing technology (VIGS) to downregulate PME gene expression, which resulted in a 30– 45 % reduction of TMV symptom severity and, correspondingly, to a 60 % reduction of TMV RNA accumulation in systemic leaves. VIGS proved to be a rapid and effective technology for PME gene silencing in functional assays and for plant defence from viral infection. Our findings indicate that N. benthamiana plants with hindered expression of PME survive a TMV infection, which kills non-silenced plants within a week.
    European Journal of Plant Pathology 10/2014; 141(2). DOI:10.1007/s10658-014-0546-y · 1.49 Impact Factor
    • "To date, among plant HGMEs, 3D crystallographic structures have only been resolved for carrot and tomato PMEs (Johansson et al., 2002; D'Avino et al., 2003; Di Matteo et al., 2005). The first crystallization of bacterial PME from Erwinia chrisanthemi was previously performed (Jenkins et al. 2001), and its co-crystallization with HGs helped in determining the key amino acids involved at the catalytic site in enzyme–substrate interactions (Fries et al., 2007). "
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    ABSTRACT: Understanding the changes affecting the plant cell wall is a key element in addressing its functional role in plant growth and in the response to stress. Pectins, which are the main constituents of the primary cell wall in dicot species, play a central role in the control of cellular adhesion and thereby of the rheological properties of the wall. This is likely to be a major determinant of plant growth. How the discrete changes in pectin structure are mediated is thus a key issue in our understanding of plant development and plant responses to changes in the environment. In particular, understanding the remodelling of homogalacturonan (HG), the most abundant pectic polymer, by specific enzymes is a current challenge in addressing its fundamental role. HG, a polymer that can be methylesterified or acetylated, can be modified by HGMEs (HG-modifying enzymes) which all belong to large multigenic families in all species sequenced to date. In particular, both the degrees of substitution (methylesterification and/or acetylation) and polymerization can be controlled by specific enzymes such as pectin methylesterases (PMEs), pectin acetylesterases (PAEs), polygalacturonases (PGs), or pectate lyases-like (PLLs). Major advances in the biochemical and functional characterization of these enzymes have been made over the last 10 years. This review aims to provide a comprehensive, up to date summary of the recent data concerning the structure, regulation, and function of these fascinating enzymes in plant development and in response to biotic stresses.
    Journal of Experimental Botany 07/2014; 65(18). DOI:10.1093/jxb/eru272 · 5.53 Impact Factor
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