ATP-dependent protease which is essential for axonal and neuron development. In neurons, mediates degradation of SMDT1/EMRE before its assembly with the uniporter complex, limiting the availability of SMDT1/EMRE for MCU assembly and promoting efficient assembly of gatekeeper subunits with MCU. Required for the maturation of paraplegin (SPG7) after its cleavage by mitochondrial-processing peptidase (MPP), converting it into a proteolytically active mature form. Required for the maturation of PINK1 into its 52kDa mature form after its cleavage by mitochondrial-processing peptidase (MPP) (By similarity). Involved in the regulation of OMA1-dependent processing of OPA1 (By similarity). Binds 1 zinc ion per subunit. Homooligomer. Forms heterooligomers with SPG7 and AFG3L1. Interacts with SPG7; the interaction is required for the efficient assembly of mitochondrial complex I. Interacts with AFG3L1. Interacts with MAIP1. Interacts with DNAJC19 and PHB2 (By similarity). Upon import into the mitochondrion, the N-terminal transit peptide is cleaved to generate an intermediate form which undergoes autocatalytic proteolytic processing to generate the proteolytically active mature form. In the N-terminal section; belongs to the AAA ATPase family. In the C-terminal section; belongs to the peptidase M41 family.