title: Structural basis for the interaction between pectin methylesterase and a specific inhibitor protein.
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.
authors.affiliation: Department of Biochemical Sciences, University of Rome, 00185 Rome, Italy.
authors.forename: Adele
authors.initials: A
authors.lastname: Di Matteo
authors.forename: Alfonso
authors.initials: A
authors.lastname: Giovane
authors.forename: Alessandro
authors.initials: A
authors.lastname: Raiola
authors.forename: Laura
authors.initials: L
authors.lastname: Camardella
authors.forename: Daniele
authors.initials: D
authors.lastname: Bonivento
authors.forename: Giulia
authors.initials: G
authors.lastname: De Lorenzo
authors.forename: Felice
authors.initials: F
authors.lastname: Cervone
authors.forename: Daniela
authors.initials: D
authors.lastname: Bellincampi
authors.forename: Demetrius
authors.initials: D
authors.lastname: Tsernoglou
mesh_terms: D029042:Actinidia / Q000737:chemistry; D000595:Amino Acid Sequence; D002265:Carboxylic Ester Hydrolases / Q000037:antagonists & inhibitors* / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000494:pharmacology*; D018551:Solanum lycopersicum / Q000201:enzymology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D010940:Plant Proteins / Q000737:chemistry* / Q000494:pharmacology*; D017510:Protein Folding; D017386:Sequence Homology, Amino Acid
chemical_list: D004791:Enzyme Inhibitors; D046912:Multiprotein Complexes; C412789:PMEI protein, Actinidia chinensis; D010940:Plant Proteins; D002265:Carboxylic Ester Hydrolases; C022323:pectinesterase
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