Activity of an atypical Arabidopsis thaliana pectin methylesterase
Abstract
An Arabidopsis thaliana pectin methylesterase that was not predicted to contain any signaling sequence was produced in E. coli and purified using a His tag added at its N-terminus. The enzyme demethylesterified Citrus pectin with a K m of 0.86 mg/ml. The enzyme did not require salt for activity and was found to be relatively temperature-sensitive. The precipitation of enzyme-treated pectin by CaCl2 suggested that the enzyme had a blockwise mode of pectin demethylesterification. A purified kiwi (Actinidia chinensis) pectin methylesterase inhibitor had no effect on the activity of the enzyme whereas it strongly inhibited a flax pectin methylesterase. A model of the protein structure revealed that an extra amino acid sequence in this particular Arabidopsis pectin methylesterase could form a ß-strand outside the core structure, which might be preventing the inhibitor from binding the protein.