Coevolution study of tau and a-synuclein suggests a connection between their normal interaction in neurons and the Parkinson's disease-associated mutation A53T

Alpha-synuclein lies at the center of Parkinson’s disease etiology, and polymorphisms in the gene for the microtubule-associated protein tau are risk factors for getting the disease. Tau and a-synuclein interact in vitro, and a-synuclein can also compete with tau binding to microtubules. To test whether these interactions might be part of their natural biological functions, a correlated mutation analysis was performed between tau and a-synuclein, looking for evidence of coevolution. For comparison, analyses were also performed between tau and b- and g-synuclein. In addition, analyses were performed between tau and the synuclein proteins and the neuronal tubulin proteins. Potential correlated mutations were detected between tau and a-synuclein, one involving an a-synuclein residue known to interact with tau in vitro, Asn122, and others involving the Parkinson’s disease-associated mutation A53T. No significant correlated mutations were seen between tau and b- and g-synuclein. Tau showed potential correlated mutations with the neuron-specific bIII-tubulin protein, encoded by the TUBB3 gene. No convincing correlated mutations were seen between the synuclein and tubulin proteins, with the possible exception of b-synuclein with bIVa-tubulin, encoded by the TUBB4A gene. While the correlated mutations between tau and a-synuclein suggest the two proteins have coevolved, additional study will be needed to confirm that their interaction is part of their normal biological function in cells.