Protein‐protein interactions reduce Ca 2+ ‐requirements for Transglutaminase 2 mediated post‐translational modifications of α‐synuclein

The combined projected increase in the incidence of Alzheimer's and Parkinson's disease is nearly 40% over the next ten years as the “baby‐boomer” population advances in age. In the majority of late onset neurodegenerative diseases, the underlying cause of neuron damage is the accumulation of toxic protein aggregates. The Ca 2+ ‐dependent, post‐translational modification of tau, α‐synuclein and β‐amyloid by transglutaminase 2 (TG2) contributes to the development of protein aggregates in the diseased brain . Vulnerable to the toxic effects of aggregated proteins, damaged neurons exhibit increased Ca 2+ ‐influx, further activating TG2. Degeneration leads to neuronal death, which gives rise to cognitive decline and dementia. The pathological TG2 protein cross‐linking activity in neuronal cells is actually beneficial to normal cellular apoptosis when regulated properly. The advancement of TG2 as a therapeutic target is hampered by the lack of fundamental understanding of how TG2 cross‐links pathogenic protein substrates. In contrast to previous in vitro mechanistic studies, which rely heavily on the use of artificial substrate analogs (i.e. Cbz‐Gln‐Gly), we present here the kinetic characterization of the TG2‐mediated, Ca 2+ deamidation and polyamidation of recombinant α‐synuclein. The apparent K m for α‐synuclein is nearly 10‐orders of magnitude lower than that for Cbz‐Gln Gly and Ca 2+ requirements for activation (K A ~0.34 μM) are significantly reduced. In addition, we explore the effects the protein‐protein interaction between TG2 and CRT, a low affinity, high capacity Ca 2+ binding protein, have on Ca 2+ ‐activation and protein cross‐linking activity. Support or Funding Information Office of Research and Graduate Studies, Brody School of Medicine