Effect of amino acids present at the carboxyl end of succinimidyl residue on the rate constants for succinimidyl hydrolysis in small peptides

Aspartate Isomerization Regulates in Situ Assembly of Peptides into Supramolecular Probes for Detection of Protein Carboxyl Methyltransferase in Bladder Cancer

Protein carboxyl methyltransferase (PCMT) restores aspartate isomers in proteins and plays a critical role in cancer prognosis. However, in vivo detection of PCMT remains challenging. Here, we report the aspartate isomerization-regulated in situ assembly of peptides into supramolecular probes within living cells for PCMT detection in bladder cancer. The peptide consists of alternating hydrophobic and hydrophilic residues and contains an isoAsp residue as a kinked site to prevent the facial amphiphilicity of the peptide. Exposure to PCMT converts isoAsp to Asp within the peptide, thereby promoting its assembly into nanofibers. Incorporation of 7-nitro-2,1,3-benzoxadiazole (NBD) into the nanofibers enables PCMT detection based on hydrophobicity-dependent fluorescence of NBD units. Both cellular and animal studies confirm the capability of supramolecular probes for efficient detection of PCMT. Our finding demonstrates an efficient strategy for regulating peptide assembly in living systems and thus provides a new tool for creation of biomedical agents in the future.

PROTEIN l-ISOASPARTYL METHYLTRANSFERASE (PIMT) in plants: regulations and functions

Proteins are essential molecules that carry out key functions in a cell. However, as a result of aging or stressful environments, the protein undergoes a range of spontaneous covalent modifications, including the formation of abnormal l-isoaspartyl residues from aspartyl or asparaginyl residues, which can disrupt the protein's inherent structure and function. PROTEIN l-ISOASPARTYL METHYLTRANSFERASE (PIMT: EC 2.1.1.77), an evolutionarily conserved ancient protein repairing enzyme (PRE), converts such abnormal l-isoaspartyl residues to normal l-aspartyl residues and re-establishes the protein's native structure and function. Although originally discovered in animals as a PRE, PIMT emerged as a key PRE in plants, particularly in seeds, in which PIMT plays a predominant role in preserving seed vigor and viability for prolonged periods of time. Interestingly, higher plants encode a second PIMT (PIMT2) protein which possesses a unique N-terminal extension, and exhibits several distinct features and far more complexity than non-plant PIMTs. Recent studies indicate that the role of PIMT is not restricted to preserving seed vigor and longevity but is also implicated in enhancing the growth and survivability of plants under stressful environments. Furthermore, expression studies indicate the tantalizing possibility that PIMT is involved in various physiological processes apart from its role in seed vigor, longevity and plant's survivability under abiotic stress. This review article particularly describes new insights and emerging interest in all facets of this enzyme in plants along with a concise comparative overview on isoAsp formation, and the role and regulation of PIMTs across evolutionary diverse species. Additionally, recent methods and their challenges in identifying isoaspartyl containing proteins (PIMT substrates) are highlighted.