Biochemical characterization of Pectin Methylesterase Inhibitor 3 from Arabidopsis thaliana

Abstract

AbstractThe Arabidopsis thaliana PECTIN METHYLESTERASE INHIBITOR 3 (PMEI3) gene is frequently used as a tool to manipulate PME activity in vivo, in studies assessing the role of pectin de-methylesterification in the control of cell expansion. One limitation of these studies is that the exact biochemical activity of this protein has not yet been determined. In this manuscript we produced the protein in Pichia pastoris and characterized its activity in vitro. Like other PMEIs, PMEI3 inhibits PME activity in acidic pH conditions for a variety of cell wall extracts and for purified PME preparations, but doesn’t affect PME activity at neutral pH. This suggests that the previously observed in vivo effects reflect the inhibition of PME activity at low pH. The protein is remarkable heat stable and shows higher activity against PME3 than against PME2, illustrating how different members of the large PMEI family can differ in their specificities towards PME targets. Finally, application of purified PMEI3 on Arabidopsis thaliana seedlings showed a dose-dependent inhibition of homogalacturonan de-methylesterification and root growth. Purified recombinant PMEI3 is therefore a powerful tool to study the connection between pectin methylesterification and cell expansion.