title: The peculiar structural features of kiwi fruit pectin methylesterase: amino acid sequence, oligosaccharides structure, and modeling of the interaction with its natural proteinaceous inhibitor.
abstract: Pectin methylesterase (PME) from kiwi fruit (Actinidia deliciosa) is a glycoprotein, showing an apparent molecular mass of 50 kDa upon size exclusion chromatography and SDS-PAGE. The primary structure, elucidated by direct sequencing of the protein, comprises 321 amino acid residues providing a molecular mass of 35 kDa. The protein has an acetylated Thr residue at the amino terminus and five N-glycosylation consensus sequences, four of which are actually glycosylated. A careful investigation of the oligosaccharide structures demonstrated that PME glycans belong to complex type oligosaccharides essentially consisting of xylosylated polyfucosylated biantennary structures. Alignment with known mature plant PME sequences indicates that the postulated active site residues are conserved. Kiwi PME activity is inhibited following the interaction with the proteinaceous inhibitor PMEI, isolated from the same source. Gel-filtration experiments show that kiwi PME/PMEI complex is stable in a large pH range and dissociates only at pH 10.0. Modeling of the interaction with the inhibitor was performed by using the crystal structure of the complex between kiwi PMEI and tomato PME as a template. The model shows that the binding site is the same reported for tomato PME. However, additional salt link interactions are found to connect the external loops of kiwi PME to PMEI. This finding may explain the higher pH stability of the complex formed by the two kiwi proteins respect to that formed by PMEI and tomato PME.
authors.affiliation: Institute of Protein Biochemistry, C.N.R., 80131 Napoli, Italy. ma.ciardiello@ibp.cnr.it
authors.forename: M Antonietta
authors.initials: MA
authors.lastname: Ciardiello
authors.forename: Rossana
authors.initials: R
authors.lastname: D'Avino
authors.forename: Angela
authors.initials: A
authors.lastname: Amoresano
authors.forename: Lisa
authors.initials: L
authors.lastname: Tuppo
authors.forename: Andrea
authors.initials: A
authors.lastname: Carpentieri
authors.forename: Vito
authors.initials: V
authors.lastname: Carratore
authors.forename: Maurizio
authors.initials: M
authors.lastname: Tamburrini
authors.forename: Alfonso
authors.initials: A
authors.lastname: Giovane
authors.forename: Piero
authors.initials: P
authors.lastname: Pucci
authors.forename: Laura
authors.initials: L
authors.lastname: Camardella
mesh_terms: D029042:Actinidia / Q000201:enzymology*; D000595:Amino Acid Sequence; D002265:Carboxylic Ester Hydrolases / Q000037:antagonists & inhibitors / Q000737:chemistry*; D004791:Enzyme Inhibitors / Q000737:chemistry*; D005638:Fruit; D008958:Models, Molecular; D009844:Oligosaccharides; D010940:Plant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry
chemical_list: D004791:Enzyme Inhibitors; D009844:Oligosaccharides; D010940:Plant Proteins; D002265:Carboxylic Ester Hydrolases; C022323:pectinesterase