Poster: Protein modification

Abs # 805: First Evidence in Eukaryotes of Active Protein L-isoaspartate/D-aspartate O-methyltransferase Enzymes Encoded by Two Genes Is Found in Arabidopsis thaliana

Presenter:	Villa, Sarah T., sdolan@ucla.edu
Authors	Villa, Sarah T. (A)   Xu, Qilong  (B)   Downie, A. Bruce (B)   Clarke, Steven G. (A)
Affiliations:	(A): University of California, Los Angeles, Department of Chemistry and Biochemistry (B): University of Kentucky, Lexington, Kentucky, Department of Horticulture

As proteins age, deamidation, isomerization, and racemization of aspartyl and asparaginyl residues contribute to the accumulation of spontaneous protein damage. The repair of age-damaged L-isoaspartyl residues is catalyzed by the protein L-isoaspartate/D-aspartate O-methyltransferase (PIMT). Using S-adenosyl-L-methionine as a methyl donor, PIMT initiates the conversion of damaged residues back to L-aspartyl via a methyl esterification reaction. It is thought that this reaction is an important repair mechanism in a wide variety of prokaryotes and eukaryotes, including higher plants. In Arabidopsis thaliana, two PIMT genes are found on chromosomes 3 (PIMT1) and 5 (PIMT2). We expressed two Arabidopsis recombinant protein splicing variants of PIMT2 in Eschericia coli and we used vapor diffusion assays to show they methylate both L-isoaspartyl and D-aspartyl residues. These PIMT2s share a similar pH and temperature activity profile with PIMT1. This is the first evidence that two genes are found in an eukaryote that produce active PIMT enzymes, and that D-aspartyl residues are substrates for plant PIMT, with the human form being the only other eukaryotic PIMT to recognize such residues.