Reassessing kinetin's effect on PINK1 and mitophagy

Substantial evidence indicates that a decline in mitochondrial health contributes to the development of Parkinson disease. Accordingly, therapeutic stimulation of mitophagy, the autophagic turnover of dysfunctional mitochondria, is a promising approach to treat Parkinson disease. An attractive target in such a setting is PINK1, a protein kinase that initiates the mitophagy cascade. Previous reports suggest that PINK1 kinase activity can be enhanced by kinetin triphosphate (KTP), an enlarged ATP analog that acts as an alternate phosphate donor for PINK1 during phosphorylation. However, the mechanism of how KTP could exert such an effect on PINK1 was unclear. In a recent study, we demonstrate that contrary to previous thinking, KTP cannot be used by PINK1. Nucleotide-bound PINK1 structures indicate that KTP would clash with the back of PINK1's ATP binding pocket, and enlarging this pocket by mutagenesis is required to enable PINK1 to use KTP. Strikingly, mutation shifts PINK1's nucleotide preference from ATP to KTP. Similar results could be demonstrated in cells with kinetin, a membrane-permeable precursor of KTP. These results overturn the previously accepted mechanism of how kinetin enhances mitophagy and indicate that kinetin and its derivatives instead function through a currently unidentified mechanism.