Protein l-isoAspartyl Methyltransferase (PIMT) and antioxidants in plants.

All life forms, including plants, accumulate reactive oxygen species (ROS) as a byproduct of metabolism; however, environmental stresses, including abiotic stresses and pathogen attacks, cause enhanced accumulation of ROS in plants. The increased accumulation of ROS often causes oxidative damage to cells. Organisms are able to maintain levels of ROS below permissible limits by several mechanisms, including efficient antioxidant systems. In addition to antioxidant systems, recent studies suggest that protein l-isoaspartyl methyltransferase (PIMT), a highly conserved protein repair enzyme across evolutionary diverse organisms, plays a critical role in maintaining ROS homeostasis by repairing isoaspartyl-mediated damage to antioxidants in plants. Under stress conditions, antioxidant proteins undergo spontaneous isoaspartyl (isoAsp) modification which is often detrimental to protein structure and function. This reduces the catalytic action of antioxidants and disturbs the ROS homeostasis of cells. This chapter focuses on PIMT and its interaction with antioxidants in plants, where PIMT constitutes a secondary level of protection by shielding a primary level of antioxidants from dysfunction and permitting them to guard during unfavorable situations.

PIMT Binding to C-Terminal Ala459 of CAIX Is Involved in Inside-Out Signaling Necessary for Its Catalytic Activity.

Human carbonic anhydrase IX (CAIX), a unique member of the α carbonic anhydrase family, is a transmembrane glycoprotein with high enzymatic activity by which CAIX contributes to tumorigenesis through pH regulation. Due to its aberrant expression, CAIX is considered to be a marker of tumor hypoxia and a poor prognostic factor of several human cancers. Hypoxia-activated catalytic function of CAIX is dependent on posttranslational modification of its short intracellular domain. In this work, we have identified that C-terminal Ala459 residue, which is common across CAIX of various species as well as additional transmembrane isoforms, plays an important role in CAIX activation and in pH regulation. Moreover, structure prediction I-TASSER analysis revealed involvement of Ala459 in potential ligand binding. Using tandem mass spectrometry, Protein-L-isoaspartyl methyltransferase (PIMT) was identified as a novel interacting partner, further confirmed by an in vitro pulldown assay and an in situ proximity ligation assay. Indeed, suppression of PIMT led to increased alkalinization of culture media of C33a cells constitutively expressing CAIX in hypoxia. We suggest that binding of PIMT represents a novel intracellular signal required for enzymatic activity of CAIX with a potential unidentified downstream function.

Genetic Modification for Improving Seed Vigor Is Transitioning from Model Plants to Crop Plants.

Although seed vigor is a complex physiological trait controlled by quantitative trait loci, technological advances in the laboratory are being translated into applications for enhancing seed vigor in crop plants. In this article, we summarize and discuss pioneering work in the genetic modification of seed vigor, especially through the over-expression of protein L-isoaspartyl methyltransferase (PIMT, EC 2.1.1.77) in seeds. The impressive success in improving rice seed vigor through the over-expression of PIMT provides a valuable reference for engineering high-vigor seeds for crop production. In recent decades, numerous genes/proteins associated with seed vigor have been identified. It is hoped that such potential candidates may be used in the development of genetically edited crops for a high and stable yield potential in crop production. This possibility is very valuable in the context of a changing climate and increasing world population.