Abstract
Mutations in the human kinase PINK1 (hPINK1) are associated with autosomal recessive early-onset Parkinson's disease (PD). hPINK1 activates Parkin E3 ligase activity, involving phosphorylation of ubiquitin and the Parkin ubiquitin-like (Ubl) domain via as yet poorly understood mechanisms. hPINK1 is unusual amongst kinases due to the presence of three loop insertions of unknown function. We report the structure of Tribolium castaneum PINK1 (TcPINK1), revealing several unique extensions to the canonical protein kinase fold. The third insertion, together with autophosphorylation at residue Ser205, contributes to formation of a bowl-shaped binding site for ubiquitin. We also define a novel structural element within the second insertion that is held together by a distal loop that is critical for TcPINK1 activity. The structure of TcPINK1 explains how PD-linked mutations that lie within the kinase domain result in hPINK1 loss-of-function and provides a platform for the exploration of small molecule modulators of hPINK1.
Highlights
Autosomal recessive inherited loss-of-function mutations in human PTEN-induced kinase 1, represent the second most frequent cause of early-onset Parkinson’s disease (PD) (Valente et al, 2004). human kinase PINK1 (hPINK1) has been proposed to act as a master regulator of mitochondrial quality control, promoting the elimination of damaged mitochondria via autophagy known as mitophagy (McWilliams and Muqit, 2017)
The molecular mechanisms of hPINK1 activation and substrate recognition are poorly understood. hPINK1 is distinct from other protein kinases due to the presence of three unique insertions (Ins1, Ins2 and Ins3) within the kinase domain and a C-terminal extension (CTE) of unknown function that bears no homology to any known protein domain (Figure 1A)
Consistent with our analysis of Tribolium castaneum PINK1 (TcPINK1) (Figure 1D), we found that Parkin and ubiquitin phosphorylation was abolished in cells expressing mutant A217D, K219A, E240K and L369P forms of hPINK1 upon carbonyl cyanide m-cholorophenylhydrazone (CCCP) stimulation (Figure 4A)
Summary
Autosomal recessive inherited loss-of-function mutations in human PTEN-induced kinase 1 (hPINK1), represent the second most frequent cause of early-onset Parkinson’s disease (PD) (Valente et al, 2004). hPINK1 has been proposed to act as a master regulator of mitochondrial quality control, promoting the elimination of damaged mitochondria via autophagy known as mitophagy (McWilliams and Muqit, 2017). Further examination of some of these features showed that they are part of human PINK1 proteins Using this new protein structure, Kumar et al went on to examine 20 mutations that are found in patients with Parkinson’s disease and have been able to show the effect that these changes have on PINK1 at a molecular level. We have elaborated an important regulatory role for TcPINK1 autophosphorylation of Serine205 (Ser205), which together with the third insertion, aids in physiological substrate recognition Overall, these findings provide molecular insights into the mechanisms of hPINK1 kinase activity, ubiquitin substrate recognition, and define the molecular basis of Parkinson’s disease-causing mutations
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