The peculiar structural features of kiwi fruit pectin methylesterase: amino acid sequence, oligosaccharides structure, and modeling of the interaction with its natural proteinaceous inhibitor.
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.
Ciardiello
M Antonietta
MA
Institute of Protein Biochemistry, C.N.R., 80131 Napoli, Italy. ma.ciardiello@ibp.cnr.it
D'Avino
Rossana
R
Amoresano
Angela
A
Tuppo
Lisa
L
Carpentieri
Andrea
A
Carratore
Vito
V
Tamburrini
Maurizio
M
Giovane
Alfonso
A
Pucci
Piero
P
Camardella
Laura
L
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
D004791:Enzyme Inhibitors; D009844:Oligosaccharides; D010940:Plant Proteins; D002265:Carboxylic Ester Hydrolases; C022323:pectinesterase