No abstract

No abstract

Act d 11 is the first member of the MLP/RRP protein family to be described as an allergen. It displays IgE co-recognition with allergens belonging to the PR-10 family, including Bet v 1.

The molecular model of Lycopersicon esculentum (tomato) pectin methylesterase (PME) was built by using the X-ray crystal structure of PME from the phytopathogenic bacterium Erwinia chrysanthemi as a template. The overall structure and the position of catalytically important residues (Asp132, Asp 153, and Arg 221, located at the bottom of the active site cleft) are conserved. Instead, loop regions forming the walls of the catalytic site are much shorter and form a less deep cleft, as already revealed by the carrot PME crystal structure. The protein inhibitor of pectin methylesterase (PMEI) isolated from kiwi fruit binds tomato PME with high affinity. Conversely, no complex formation between the inhibitor and PME from E. chrysanthemi is observed, and the activity of this enzyme is unaffected by the presence of the inhibitor. Fluorescence quenching experiments on tomato PME and on PME-PMEI complex suggest that tryptophanyl residues present in the active site region are involved in the interaction and that the inhibitor interacts with plant PME at the level of the active site. We also suggest that the more open active site cleft of tomato PME allows the interaction with the inhibitor. Conversely, the narrow and deep cleft of the active site of E. chrysanthemi PME hinders this interaction. The pH-dependent changes in fluorescence emission intensity observed in tomato PME could arise as the result of protonation of an Asp residue with unusually high pKa, thus supporting the hypothesis that Asp132 acts as acid/base in the catalytic cycle.

A pectin methylesterase inhibitor (SolyPMEI) from tomato has been identified and characterised by a functional genomics approach. SolyPMEI is a cell wall protein sharing high similarity with Actinidia deliciosa PMEI (AdPMEI), the best characterised inhibitor from kiwi. It typically affects the activity of plant pectin methylesterases (PMEs) and is inactive against a microbial PME. SolyPMEI transcripts were mainly expressed in flower, pollen and ripe fruit where the protein accumulated at breaker and turning stages of ripening. The expression of SolyPMEI correlated during ripening with that of PME-1, the major fruit specific PME isoform. The interaction of SolyPMEI with PME-1 was demonstrated in ripe fruit by gel filtration and by immunoaffinity chromatography. The analysis of the zonal distribution of PME activity and the co-localization of SolyPMEI with high esterified pectins suggest that SolyPMEI regulates the spatial patterning of distribution of esterified pectins in fruit.