L attività pectina metilesterasica (PME) e il suo controllo nella cellula vegetale.

Résumé / Abstract Pectin methylesterase (PME) is present in plants and phytopathogenic microorganisms (bacteria and fungi) and is the first enzyme acting on pectin, which thereafter can be degraded by glycosidases. PME is present in plant as several isoforms, which are encoded by a multigene family (in Arabidopsis genome 67 PME-related genes have been identified). Regulation of plant PME occurs through the differential expression of isoforms in different tissues and developmental stages. In addition, the identification of a proteinaceous inhibitor (PMEI) specific for plant PMEs suggests the existence of a post-translational control mechanism. PMEI has been biochemically identified only in kiwi fruit. It has been recently shown that two gene sequences from Arabidopsis, cloned and expressed in a heterologous system, produce proteins having PMEI activity. The kiwi PMEI primary structure analysis has identified a structural motif consisting of 4 cysteines linked by disulfide bridge, first to second and third to fourth. This structural motif is also found in other plant proteins, the inhibitors of invertase, which have different target enzymes. PMEI has an interesting biotechnological application in food industry as inhibitor of endogenous PME, responsible for phase separation and cloud loss in fruit juice manufacturing.