Biochemical characterization and molecular insights into substrate recognition of pectin methylesterase from Phytophthora infestans

Pectin methylesterases (PMEs) are a class of carbohydrate-active enzymes that act on the O6-methyl ester groups of the homogalacturonan component of pectins, resulting in de-esterification of the sub-strate polymers and formation of pectate and methanol. PMEs occur in higher plants and microorgan-isms, including fungi, oomycetes, bacteria, and archaea. Microbial PMEs play a crucial role in pathogens' invasion of plant tissues. Here, we have determined the structural and functional properties of Pi-PME, a PME from the oomycete plant pathogen Phytophthora infestans. This enzyme exhibits maxi-mum activity at alkaline pH (8.5) and is active over a wide temperature range (25-50 degrees C). In silico deter-mination of the structure of Pi-PME reveals that the protein consists essentially of three parallel 8-sheets interconnected by loops that adopt an overall 8-helix organization. The loop regions in the vicinity of the active site are extended compared to plant and fungal PMEs, but they are shorter than the corresponding bacterial and insect regions. Molecular dynamic simulations revealed that Pi-PME interacts most strongly with partially de-methylated homogalacturonans, suggesting that it preferentially uses this type of sub-strates. The results are compared and discussed with other known PMEs from different organisms, high-lighting the specific features of Pi-PME.(c) 2022 The Authors. Published by Elsevier B.V. on behalf of Research Network of Computational and Structural Biotechnology. This is an open access article under the CC BY-NC-ND license (http://creative-commons.org/licenses/by-nc-nd/4.0/).

Automated summary

The structural and functional properties of Pi-PME, a PME from the oomycete plant pathogen Phytophthora infestans, have been determined. Pi-PME exhibits maximum activity at alkaline pH and a wide temperature range. Molecular dynamic simulations show that Pi-PME interacts most strongly with partially demethylated homogalacturonans, indicating its preference for this type of substrate.