title: Influence of pH on the Structure and Function of Kiwi Pectin Methylesterase Inhibitor.
abstract: Pectin methylesterase is a pectin modifying enzyme that plays a key role in plant physiology. It is also an important quality-related enzyme in plant-based food products. The pectin methylesterase inhibitor (PMEI) from kiwifruit inhibits this enzyme activity and is widely used as an efficient tool for research purposes and also recommended in the context of fruit and vegetable processing. Using several methodologies of protein biochemistry, including circular dichroism and fluorescence spectroscopy, chemical modifications, direct protein-sequencing, enzyme activity, and bioinformatics analysis of the crystal structure, this study demonstrates that conformational changes occur in kiwi PMEI by the pH rising over 6.0 bringing about structure loosening, exposure, and cleavage of a natively buried disulfide bond, unfolding and aggregation, ultimately determining the loss of ability of kiwi PMEI to bind and inhibit PME. pH-induced structural changes are prevented when PMEI is already engaged in complex or is in a solution of high ionic strength.
authors.affiliation: Institute of Biosciences and BioResources, C.N.R. , Napoli, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Bonavita
authors.affiliation: Institute of Biosciences and BioResources, C.N.R. , Napoli, Italy.
authors.forename: Vitale
authors.initials: V
authors.lastname: Carratore
authors.affiliation: Institute of Biosciences and BioResources, C.N.R. , Napoli, Italy.
authors.forename: Maria Antonietta
authors.initials: MA
authors.lastname: Ciardiello
authors.affiliation: Department of Biochemistry, Biophysics and General Pathology, Second University of Napoli , Napoli, Italy.
authors.forename: Alfonso
authors.initials: A
authors.lastname: Giovane
authors.affiliation: Department of Biochemistry, Biophysics and General Pathology, Second University of Napoli , Napoli, Italy.
authors.forename: Luigi
authors.initials: L
authors.lastname: Servillo
authors.affiliation: Institute of Biosciences and BioResources, C.N.R. , Napoli, Italy.
authors.forename: Rossana
authors.initials: R
authors.lastname: D'Avino
mesh_terms: D029042:Actinidia / Q000201:enzymology* / Q000235:genetics; D000595:Amino Acid Sequence; D002265:Carboxylic Ester Hydrolases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002942:Circular Dichroism; D004791:Enzyme Inhibitors / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D010940:Plant Proteins; D002265:Carboxylic Ester Hydrolases; C022323:pectinesterase
keywords: Actinidia deliciosa; kiwi pectin methylesterase inhibitor (PMEI); pH-dependent protein stability; pH-induced conformational changes; pectin methylesterase; protein−inhibitor interaction; thiol−disulfide reshuffling; unfolding