SPG7
Function
Catalytic component of the m-AAA protease, a protease that plays a key role in proteostasis of inner mitochondrial membrane proteins, and which is essential for axonal and neuron development (PubMed:11549317, PubMed:28396416, PubMed:31097542, PubMed:9635427). SPG7 possesses both ATPase and protease activities: the ATPase activity is required to unfold substrates, threading them into the internal proteolytic cavity for hydrolysis into small peptide fragments (By similarity). The m-AAA protease exerts a dual role in the mitochondrial inner membrane: it mediates the processing of specific regulatory proteins and ensures protein quality control by degrading misfolded polypeptides (By similarity). Mediates protein maturation of the mitochondrial ribosomal subunit MRPL32/bL32m by catalyzing the cleavage of the presequence of MRPL32/bL32m prior to assembly into the mitochondrial ribosome (By similarity). Acts as a regulator of calcium in neurons by mediating 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 (PubMed:28396416, PubMed:31097542). Also regulates mitochondrial calcium by catalyzing degradation of MCU (PubMed:31097542). Plays a role in the formation and regulation of the mitochondrial permeability transition pore (mPTP) and its proteolytic activity is dispensable for this function (PubMed:26387735).
Involvement in disease
Spastic paraplegia 7, autosomal recessive
SPG7
A form of spastic paraplegia, a neurodegenerative disorder characterized by a slow, gradual, progressive weakness and spasticity of the lower limbs. Rate of progression and the severity of symptoms are quite variable. Initial symptoms may include difficulty with balance, weakness and stiffness in the legs, muscle spasms, and dragging the toes when walking. In some forms of the disorder, bladder symptoms (such as incontinence) may appear, or the weakness and stiffness may spread to other parts of the body. SPG7 is a complex form. Additional clinical features are cerebellar syndrome, supranuclear palsy, and cognitive impairment, particularly disturbance of attention and executive functions.
None
The disease is caused by variants affecting the gene represented in this entry.
Defects in SPG7 may cause autosomal recessive osteogenesis imperfecta (OI). Osteogenesis imperfecta defines a group of connective tissue disorders characterized by bone fragility and low bone mass. Clinical features of SPG7-related osteogenesis imperfecta include recurrent fractures, mild bone deformities, delayed tooth eruption, normal hearing and white sclera.
Post-translational modifications
Upon import into the mitochondrion, the N-terminal transit peptide is cleaved by the mitochondrial-processing peptidase (MPP) to generate an intermediate form which undergoes a second proteolytic cleavage mediated by proteases AFG3L2 removing an additional N-terminal fragment to generate the proteolytically active mature form.
Sequence Similarities
In the N-terminal section; belongs to the AAA ATPase family.
In the C-terminal section; belongs to the peptidase M41 family.
Tissue Specificity
Ubiquitous.
Cellular localization
- Mitochondrion inner membrane
- Multi-pass membrane protein
Alternative names
CAR, CMAR, PGN, SPG7, Mitochondrial inner membrane m-AAA protease component paraplegin, Cell matrix adhesion regulator, Paraplegin, Spastic paraplegia 7 protein