Isoaspartate accumulation in creatine kinase B in vivo and in vitro is associated with loss of enzymatic activity (949.1)

Abstract

Formation of abnormal isoaspartyl (isoAsp) residues occurs frequently in proteins and peptides under physiological conditions, often resulting in the alteration of their structure and function. IsoAsp residues can be efficiently repaired by the action of protein L‐isoaspartyl O‐methyltransferase (PIMT), a cellular repair enzyme that catalyzes the conversion of isoAsp to normal Asp residues. The brain‐enriched isoform of creatine kinase (CK‐B) plays a key role in intracellular energy metabolism and is highly susceptible to isoAsp formation. We investigated the effect of isoAsp formation on CK‐B activity, both in vivo in PIMT‐deficient mice, and in vitro using aged recombinant CK‐B. Accumulation of isoAsp residues in vivo was associated with a significant decrease in CK‐B activity. In vitro aging of recombinant human CK‐B also resulted in isoAsp formation and loss of CK‐B activity. IsoAsp sites in aged, recombinant CK‐B were efficiently repaired in vitro by the action of PIMT. These results (1) corroborate previous finding that CK‐B is a major target of PIMT action in vivo, (2) demonstrate that isoAsp accumulation in CK‐B is associated with significant loss of function, and (3) suggest that loss of CK‐B function in vivo may contribute to the neuropathology and susceptibility to epileptic seizures that are characteristic of PIMT‐deficient mice.Grant Funding Source: Supported by NIH grant NS‐17269