Isomerization of l -aspartyl and l -asparaginyl residues to l -isoaspartyl residues is one type of protein damage that can occur under physiological conditions and leads to conformational changes, loss of function, and enhanced protein degradation. Protein l -isoaspartyl methyltransferase (PCMT) is a repair enzyme whose action initiates the reconversion of abnormal l -isoaspartyl residues to normal l -aspartyl residues in proteins. Many lines of evidence support a crucial role for PCMT in the brain, but the mechanisms involved remain poorly understood. Here, we investigated PCMT activity and function in zebrafish, a vertebrate model that is particularly well-suited to analyze brain function using a variety of t... More
Isomerization of l -aspartyl and l -asparaginyl residues to l -isoaspartyl residues is one type of protein damage that can occur under physiological conditions and leads to conformational changes, loss of function, and enhanced protein degradation. Protein l -isoaspartyl methyltransferase (PCMT) is a repair enzyme whose action initiates the reconversion of abnormal l -isoaspartyl residues to normal l -aspartyl residues in proteins. Many lines of evidence support a crucial role for PCMT in the brain, but the mechanisms involved remain poorly understood. Here, we investigated PCMT activity and function in zebrafish, a vertebrate model that is particularly well-suited to analyze brain function using a variety of techniques. We characterized the expression products of the zebrafish PCMT homologous genes pcmt and pcmtl . Both zebrafish proteins showed a robust l -isoaspartyl methyltransferase activity and highest mRNA transcript levels were found in brain and testes. Zebrafish morphant larvae with a knockdown in both the pcmt and pcmtl genes showed pronounced morphological abnormalities, decreased survival, and increased isoaspartyl levels. Interestingly, we identified a profound perturbation of brain calcium homeostasis in these morphants. An abnormal calcium response upon ATP stimulation was also observed in mouse hippocampal HT22 cells knocked out for Pcmt1 . This work shows that zebrafish is a promising model to unravel further facets of PCMT function and demonstrates, for the first time in vivo , that PCMT plays a pivotal role in the regulation of calcium fluxes.
