Serine/threonine-protein kinase which protects against mitochondrial dysfunction during cellular stress by phosphorylating mitochondrial proteins such as PRKN and DNM1L, to coordinate mitochondrial quality control mechanisms that remove and replace dysfunctional mitochondrial components (PubMed:24652937, PubMed:24784582, PubMed:25474007, PubMed:32484300). Depending on the severity of mitochondrial damage and/or dysfunction, activity ranges from preventing apoptosis and stimulating mitochondrial biogenesis to regulating mitochondrial dynamics and eliminating severely damaged mitochondria via mitophagy (By similarity). Mediates the translocation and activation of PRKN at the outer membrane (OMM) of dysfunctional/depolarized mitochondria (PubMed:24652937, PubMed:24784582, PubMed:25474007, PubMed:32484300). At the OMM of damaged mitochondria, phosphorylates pre-existing polyubiquitin chains at 'Ser-65', the PINK1-phosphorylated polyubiquitin then recruits PRKN from the cytosol to the OMM where PRKN is fully activated by phosphorylation at 'Ser-65' by PINK1 (PubMed:24652937, PubMed:24784582, PubMed:25474007, PubMed:32484300). In damaged mitochondria, mediates the decision between mitophagy or preventing apoptosis by promoting PRKN-dependent poly- or monoubiquitination of VDAC1; polyubiquitination of VDAC1 by PRKN promotes mitophagy, while monoubiquitination of VDAC1 by PRKN decreases mitochondrial calcium influx which ultimately inhibits apoptosis (By similarity). When cellular stress results in irreversible mitochondrial damage, functions with PRKN to promote clearance of damaged mitochondria via selective autophagy (mitophagy) (PubMed:24784582, PubMed:25474007). The PINK1-PRKN pathway also promotes fission of damaged mitochondria by phosphorylating and thus promoting the PRKN-dependent degradation of mitochondrial proteins involved in fission such as MFN2 (By similarity). This prevents the refusion of unhealthy mitochondria with the mitochondrial network or initiates mitochondrial fragmentation facilitating their later engulfment by autophagosomes (By similarity). Also promotes mitochondrial fission independently of PRKN and ATG7-mediated mitophagy, via the phosphorylation and activation of DNM1L (PubMed:32484300). Regulates motility of damaged mitochondria by promoting the ubiquitination and subsequent degradation of MIRO1 and MIRO2; in motor neurons, this likely inhibits mitochondrial intracellular anterograde transport along the axons which probably increases the chance of the mitochondria undergoing mitophagy in the soma (By similarity). Required for ubiquinone reduction by mitochondrial complex I by mediating phosphorylation of complex I subunit NDUFA10 (PubMed:24652937). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with PRKN (By similarity). Interacts with FBXO7 (By similarity). Forms a complex with PRKN and PARK7 (PubMed:19229105). Interacts with NENF (PubMed:31536960). Localizes mostly in mitochondrion and the two smaller proteolytic processed fragments localize mainly in cytosol. When mitochondria lose mitochondrial membrane potential following damage, PINK1 import is arrested, which induces its accumulation in the outer mitochondrial membrane, where it acquires kinase activity. High levels expressed in testis, lower levels in brain, heart, lung, liver and kidney. Proteolytically cleaved. In healthy cells, the precursor is continuously imported into the inner mitochondrial membrane (IMM), where it is proteolytically cleaved by mitochondrial-processing peptidase (MPP) and then undergoes further proteolytic cleavage by PARL or AFG3L2 to give rise to the 52 kDa short form. The 52 kDa short form is then released into the cytosol where it rapidly undergoes proteasome-dependent degradation. In unhealthy cells, when cellular stress conditions lead to the loss of mitochondrial membrane potential, mitochondrial import is impaired leading to the precursor accumulating on the outer mitochondrial membrane (OMM). If accumulation at the OMM fails and it is imported into the depolarized mitochondria, it undergoes cleavage by the IMM protease OMA1, promoting its subsequent degradation by the proteasome. Autophosphorylated (PubMed:25474007). Loss of mitochondrial membrane potential results in the precursor accumulating on the outer mitochondrial membrane (OMM) where it is activated by autophosphorylation (By similarity). Autophosphorylation at Ser-227 and Ser-401 is essential for selective recruitment of PRKN to depolarized mitochondria, via PINK1-dependent phosphorylation of ubiquitin and PRKN (By similarity). Mitochondrial dysfunction (PubMed:18687901, PubMed:20049710, PubMed:32484300). Mice do not show gross structural defects in mitochondria, although the number of larger mitochondria is selectively increased (PubMed:18687901, PubMed:32484300). Mitochondrial respiration is impaired in the striatum, which is rich in dopaminergic terminals, but not in the cerebral cortex in young mice (PubMed:18687901). Mitochondrial respiration activities in the cerebral cortex are decreased in 2 years old mice (PubMed:18687901). Mice show defects in mitochondrial complex I and a decrease in mitochondrial membrane potential (PubMed:20049710). Decreased phosphorylation of Dnm1l in embryonic fibroblasts and in the substantial nigra of 18 month old mice (PubMed:32484300). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.