Substrate specificity of plant and fungi pectin methylesterases: Identification of novel inhibitors of PMEs

Pectin methylesterases (PMEs) play a central role in pectin remodeling during plant development. They are also present in phytopathogens such as bacteria and fungi. We investigated the substrate specificity and pH dependence of plant and fungi PMEs using tailor-made pectic substrates. For this purpose, we used two plant PMEs (from orange peel: Citrus sinensis and from Arabidopsis thaliana) and one fungal PME (from Botrytis cinerea). We showed that plant and fungi PMEs differed in their substrate specificity and pH dependence, and that there were some differences between plant PMEs. We further investigated the inhibition of these enzyme activities using characterized polyphenols such as catechins and tannic acid. We showed that PMEs differed in their sensitivity to chemical compounds. In particular, fungal PME was not sensitive to inhibition. Finally, we screened for novel chemical inhibitors of PMEs using a chemical library of ∼3600 compounds. We identified a hundred new inhibitors of plant PMEs, but none had an effect on the fungal enzyme. This study sheds new light on the specificity of pectin methylesterases and provides new tools to modulate their activity.