Evolutionary analysis of PINK1 reveals key roles of the N- and C-terminal extensions and TOM20 in folding its kinase domain

PINK1 is a mitochondrial serine/threonine kinase that plays a crucial role in initiating ubiquitin-dependent mitophagy. Mutations in the gene that encodes PINK1 can cause early-onset Parkinson's disease. Although PINK1 has been studied in various insect species, obtaining a soluble and active version of the human version of the protein (HsPINK1) has been difficult, hindering further research.

A recent study investigated the evolutionary differences between PINK1 in various metazoan species. By comparing the 48 PINK1 orthologues, researchers found that the ability to bind to the mitochondrial import receptor TOM20 is a characteristic exclusive to vertebrates. This binding is associated with the divergence of the PINK1 N- and C-terminal extensions (NTE and CTE). Invertebrate PINK1 orthologues functioned as active kinases, whereas their vertebrate counterparts did not exhibit detectable ubiquitin kinase activity.

Using nuclear magnetic resonance (NMR) spectroscopy, the researchers discovered that introducing ten specific residues from the NTE-CTE interface of the Tribolium castaneum PINK1 (TcPINK1) into the humanized version of the kinase domain enables direct binding to human TOM20. Furthermore, co-expression of TOM20 with the recombinant HsPINK1 significantly enhanced its activity.

Based on these evolutionary differences, the researchers engineered a chimeric PINK1 protein that incorporated a predominantly human kinase domain, supported by the NTE-CTE elements derived from TcPINK1. This chimeric protein was found to be catalytically active and required compatible interactions between the NTE-CTE and the kinase C-lobe for optimal function. The findings also suggest that R152W is a likely pathogenic variant of PINK1.

Overall, these results provide insights into the molecular mechanisms underlying PINK1 stability and activity, highlighting the importance of the NTE and CTE in regulating the kinase's function. The study also suggests that vertebrate PINK1 has evolved a greater reliance on the mitochondrial import machinery to maintain its functional state.