Protein L-isoaspartyl methyltransferase1 (CaPIMT1) from chickpea mitigates oxidative stress-induced growth inhibition of Escherichia coli.

PROTEIN L-ISOASPARTYL METHYLTRANSFERASE (PIMT) repairs deleterious L-isoaspartyl residues synthesized spontaneously in proteins due to aging or stressful environments and is widespread in living organisms including plants. Even though PIMT activity has been detected from various plant sources, detailed studies are limited to a few species. Our present study on a chickpea (Cicer arietinum) PIMT reveals that apart from seed, PIMT activity is present in other organs and noticeably enhanced during stressful conditions. Using degenerate oligonucleotides and RACE strategy, a full length cDNA (CaPIMT1) was cloned and sequenced. The cDNA is 920 bp in length and contains only one open reading frame of 690 bp encoding 229 amino acids. Genomic structure reveals that the CaPIMT1 gene spans about 2,050 bp in length and contains four exons and three introns. By quantitative real-time RT-PCR, we demonstrate that the transcript of CaPIMT1 is distributed across the organs with maximum levels in seed and is also enhanced under various environmental stress conditions. Purified bacterially expressed protein is further characterized for its catalytic properties. The activity is found to be elevated towards high temperature and pH conditions. Escherichia coli expressing CaPIMT1 show greater tolerance to oxidative stress than E. coli without CaPIMT1. Taken together, our results suggest that PIMT from chickpea shows a distinct pattern of expression and may have a specific role in stress adaptation apart from seed.