Pectin O-3 deacetylation by Arabidopsis thaliana pectin acetylesterase 11 is important for sequential homogalacturonan degradation.

Pectin is a complex plant cell wall polysaccharide whose galacturonic acid residues can be acetylated at O-2 and/or O-3 positions. The degree of acetylation is regulated by pectin acetyl esterase (PAE, EC 3.1.1.6). However, the structure and function of plant PAEs is unclear, impairing our understanding of the role of the fine-tuning of pectin acetylation in the control of plant development. This study highlights the importance of AtPAE11 from Arabidopsis thaliana in fine tuning of pectin acetylation. AtPAE11 was heterologously expressed in HEK cells and purified by affinity chromatography. AtPAE11 exhibited activity across a broad pH range (3.5-7.5), with an optimal temperature of 30 °C. Nuclear magnetic resonance spectroscopy, supported by molecular docking, indicated a specific activity toward O-3 acetylated homogalacturonan (HG), with reduced activity on methylesterified HG. Mass spectrometry analyses showed no AtPAE11 activity on lyase-treated HG. Enzymatic pretreatment of pectin using pectin methylesterase and AtPAE11 slightly enhanced the oligogalacturonides formation by HG lyase activity, indicating a sequential degradation mechanism. Additionally, AtPAE11 treatment improved the stiffness of sugar beet pectin gel, opening new possibilities for pectin valorization. These findings provide new insights into the function of PAEs in plants and identify AtPAE11 as a highly specific enzyme.