Biochemical characterization of an Arabidopsis pectin methylesterase AtPME3 and a pectin methylesterase inhibitor
Abstract
Pectin methylesterase (PME) catalyses the de-methylesterification of pectin in plant cell walls during cell elongation. While it is generally assumed that fungal PMEs have a random mode of action, plant PMEs are thought to act in a processive manner to generate long stretches of non-methylesterified residues. However, it is unlikely that all plant PMEs have a strictly similar mode of action. One A. thalianaPME gene (PME3) has been over-expressed in an heterologous system and its protein product purified by affinity chromatography. Homogalacturonans (HGs) from citrus pectin with varied degrees of methyl esterification (DM) have been generated and characterized. Kinetic properties of PME3 have been determined. PME activity from the purified PME3 was performed on the characterized HG substrates with respect to pH. PME3 shows a highest activity at a basic pH but displays different affinities towards specific methyl esterification patterns on the pectin substrates. Demethylesterified blocks assessed by measuring the degree of blockiness and absolute degree of blockiness will be presented. PME activities are also regulated by endogenous pectin methylesterase inhibitors (PMEIs), which control the DM of HG. PMEI7 inhibits PME3 enzyme activity. Docking analysis indicates that the inhibition of PME3 occurs via the PMEI7 interaction with a PME ligand-binding cleft structure.