Variable and Tissue-Specific Subunit Composition of Mitochondrial m -AAA Protease Complexes Linked to Hereditary Spastic Paraplegia (original) (raw)
Related papers
Cell, 2005
AAA proteases comprise a conserved family of membrane bound ATP-dependent proteases that ensures the quality control of mitochondrial inner-membrane proteins. Inactivation of AAA proteases causes pleiotropic phenotypes in various organisms, including respiratory deficiencies, mitochondrial morphology defects, and axonal degeneration in hereditary spastic paraplegia (HSP). The molecular basis of these defects, however, remained unclear. Here, we describe a regulatory role of an AAA protease for mitochondrial protein synthesis in yeast. The mitochondrial ribosomal protein MrpL32 is processed by the m-AAA protease, allowing its association with preassembled ribosomal particles and completion of ribosome assembly in close proximity to the inner membrane. Maturation of MrpL32 and mitochondrial protein synthesis are also impaired in a HSP mouse model lacking the m-AAA protease subunit paraplegin, demonstrating functional conservation. Our findings therefore rationalize mitochondrial defects associated with m-AAA protease mutants in yeast and shed new light on the mechanism of axonal degeneration in HSP.
The Journal of cell …, 2003
utations in paraplegin, a putative mitochondrial metallopeptidase of the AAA family, cause an autosomal recessive form of hereditary spastic paraplegia (HSP). Here, we analyze the function of paraplegin at the cellular level and characterize the phenotypic defects of HSP patients' cells lacking this protein. We demonstrate that paraplegin coassembles with a homologous protein, AFG3L2, in the mitochondrial inner membrane. These two proteins form a high molecular mass complex, which we show to be aberrant in HSP fibroblasts. The loss of this M complex causes a reduced complex I activity in mitochondria and an increased sensitivity to oxidant stress, which can both be rescued by exogenous expression of wild-type paraplegin. Furthermore, complementation studies in yeast demonstrate functional conservation of the human paraplegin-AFG3L2 complex with the yeast m-AAA protease and assign proteolytic activity to this structure. These results shed new light on the molecular pathogenesis of HSP and functionally link AFG3L2 to this neurodegenerative disease.
m-AAA proteases, mitochondrial calcium homeostasis and neurodegeneration
Cell research, 2018
The function of mitochondria depends on ubiquitously expressed and evolutionary conserved m-AAA proteases in the inner membrane. These ATP-dependent peptidases form hexameric complexes built up of homologous subunits. AFG3L2 subunits assemble either into homo-oligomeric isoenzymes or with SPG7 (paraplegin) subunits into hetero-oligomeric proteolytic complexes. Mutations in AFG3L2 are associated with dominant spinocerebellar ataxia (SCA28) characterized by the loss of Purkinje cells, whereas mutations in SPG7 cause a recessive form of hereditary spastic paraplegia (HSP7) with motor neurons of the cortico-spinal tract being predominantly affected. Pleiotropic functions have been assigned to m-AAA proteases, which act as quality control and regulatory enzymes in mitochondria. Loss of m-AAA proteases affects mitochondrial protein synthesis and respiration and leads to mitochondrial fragmentation and deficiencies in the axonal transport of mitochondria. Moreover m-AAA proteases regulate ...
Genomics, 2001
The identification of SPG7 as the gene defective in a recessive form of spastic paraplegia has drawn attention to the yeast protein family of ATP-dependent zinc metalloproteases. The protein encoded by SPG7, paraplegin, shows high homology to members of this protein family. Recently, many mammalian ATP-dependent zinc metalloproteases have been identified and considered as possible candidates for defects in other forms of hereditary spastic paraplegia and possibly other neurodegenerative disorders. So far only a partial sequence has been available for one of those genes, ATPase family gene-3, yeast-like-1 (AFG3L1). We have carried out detailed molecular analysis of this gene and identified and characterized its mouse orthologue, Afg3l1. Our data indicate that AFG3L1 is transcribed into four mRNA isoforms that are not translated in humans. Afg3l1 encodes a protein with high homology to paraplegin and the other members of the ATP-dependent zinc metalloprotease family. Like the other ATP-dependent zinc metalloproteases, Afg3l1 localizes to the mitochondria.
The Mitochondrial Protease AFG3L2 Is Essential for Axonal Development
Journal of Neuroscience, 2008
The mitochondrial metalloprotease AFG3L2 assembles with the homologous protein paraplegin to form a supracomplex in charge of the essential protein quality control within mitochondria. Mutations of paraplegin cause a specific axonal degeneration of the upper motoneuron and, therefore, hereditary spastic paraplegia. Here we present two Afg3l2 murine models: a newly developed null and a spontaneous mutant that we found carrier of a missense mutation. Contrasting with the mild and late onset axonal degeneration of paraplegin-deficient mouse, Afg3l2 models display a marked impairment of axonal development with delayed myelination and poor axonal radial growth leading to lethality at P16. The increased severity of the Afg3l2 mutants is explained by two main molecular features that differentiate AFG3L2 from paraplegin: its higher neuronal expression and its versatile ability to support both hetero-oligomerization and homo-oligomerization. Our data assign to AFG3L2 a crucial role by linking mitochondrial metabolism and axonal development. Moreover, we propose AFG3L2 as an excellent candidate for motoneuron and cerebellar diseases with early onset unknown etiology.
Human Molecular Genetics, 2009
The mitochondrial m-AAA protease has a crucial role in axonal development and maintenance. Human mitochondria possess two m-AAA protease isoenzymes: a hetero-oligomeric complex, composed of paraplegin and AFG3L2 (Afg3 like 2), and a homo-oligomeric AFG3L2 complex. Loss of function of paraplegin (encoded by the SPG7 gene) causes hereditary spastic paraplegia, a disease characterized by retrograde degeneration of cortical motor axons. Spg7 2/2 mice show a late-onset degeneration of long spinal and peripheral axons with accumulation of abnormal mitochondria. In contrast, Afg3l2 Emv66/Emv66 mutant mice, lacking the AFG3L2 protein, are affected by a severe neuromuscular phenotype, due to defects in motor axon development. The role of the homo-oligomeric m-AAA protease and the extent of cooperation and redundancy between the two isoenzymes in adult neurons are still unclear. Here we report an early-onset severe neurological phenotype in Spg7 2/ 2 Afg3l2 Emv66/1 mice, characterized by loss of balance, tremor and ataxia. Spg7 2/2 Afg3l2 Emv66/1 mice display acceleration and worsening of the axonopathy observed in paraplegindeficient mice. In addition, they show prominent cerebellar degeneration with loss of Purkinje cells and parallel fibers, and reactive astrogliosis. Mitochondria from affected tissues are prone to lose mt-DNA and have unstable respiratory complexes. At late stages, neurons contain structural abnormal mitochondria defective in COX-SDH reaction. Our data demonstrate genetic interaction between the m-AAA isoenzymes and suggest that different neuronal populations have variable thresholds of susceptibility to reduced levels of the m-AAA protease. Moreover, they implicate impaired mitochondrial proteolysis as a novel pathway in cerebellar degeneration.
Mutations in the mitochondrial protease gene AFG3L2 cause dominant hereditary ataxia SCA28
Nature Genetics, 2010
Autosomal dominant SCAs are a clinically and genetically heterogeneous group of neurological disorders primarily characterized by imbalance, progressive gait and limb ataxia, and dysarthria 1-3 , caused by degeneration of the cerebellum and its afferent and efferent connections 2-5. Twenty-eight SCA loci are currently known, and 16 seemingly unrelated disease genes have been identified thus far 3 (http://neuromuscular.wustl.edu/ataxia/domatax.html). In ten types of ataxia, the disease is caused by dynamic expansions of polyglutamine-encoding CAG repeats 4,6 (SCA types 1, 2, 3, 6, 7 and 17, and dentatorubral-pallidoluysian atrophy) or repeats falling outside the coding region 7 (SCA types 10, 12 and 31) in genes whose function is still largely unknown. In recent years, a group of SCAs have emerged that are caused by conventional mutations in specific genes (SCA types 5, 11, 13, 14, 15/16/29 and 27). The distinct functions of these disease genes have revealed the complex heterogeneity of the pathogenic mechanisms leading to cerebellar degeneration and ataxia 3. We had mapped a previously unidentified SCA locus (SCA28) on chromosome 18p11.22-q11.2 in a four-generation Italian family with an autosomal dominant form of cerebellar ataxia 8 (ADCA type I (ref. 1)). On the basis of expression profiles in the nervous system, we selected 12 genes within the 7.9-megabase critical region, including that encoding the mitochondrial metalloprotease AFG3L2 (ATPase family gene 3-like 2). Although no dominant ataxia has thus far been associated with mitochondrial dysfunction, we focused on this gene because of its partnership with paraplegin, a cognate mitochondrial protease, the loss of which causes a distinct neurodegenerative disorder, the recessively inherited form of hereditary spastic paraplegia SPG7 (ref. 9). AFG3L2 and paraplegin are highly homologous (40-45% amino acid identity) to two yeast mitochondrial proteins, Yta10p (Afg3p) and Yta12p (Rca1p), respectively, belonging to the superfamily of P-loop ATPases known as ATPases associated with various cellular activities, or AAA+ (ref. 10). They contain an ATP-binding/ATPase domain (AAA domain), the structural hallmark of the AAA-protease subfamily 11,12 , and a zinc-dependent metalloprotease domain in a single polypeptide (Fig. 1), and they form large proteolytic complexes in the mitochondrial inner membrane that are active on the matrix side (m-AAA protease) 12. In humans, m-AAA is composed of paraplegin and AFG3L2. A third m-AAA subunit paralog, AFG3L1, is expressed in mouse but is encoded by a pseudogene in humans 13. In yeast, the m-AAA is a hetero-oligomer composed of Yta10p and Yta12p subunits. By contrast, both homo-oligomeric AFG3L2-AFG3L2 and
PLoS Genetics, 2011
We report an early onset spastic ataxia-neuropathy syndrome in two brothers of a consanguineous family characterized clinically by lower extremity spasticity, peripheral neuropathy, ptosis, oculomotor apraxia, dystonia, cerebellar atrophy, and progressive myoclonic epilepsy. Whole-exome sequencing identified a homozygous missense mutation (c.1847G.A; p.Y616C) in AFG3L2, encoding a subunit of an m-AAA protease. m-AAA proteases reside in the mitochondrial inner membrane and are responsible for removal of damaged or misfolded proteins and proteolytic activation of essential mitochondrial proteins. AFG3L2 forms either a homo-oligomeric isoenzyme or a hetero-oligomeric complex with paraplegin, a homologous protein mutated in hereditary spastic paraplegia type 7 (SPG7). Heterozygous loss-of-function mutations in AFG3L2 cause autosomal-dominant spinocerebellar ataxia type 28 (SCA28), a disorder whose phenotype is strikingly different from that of our patients. As defined in yeast complementation assays, the AFG3L2 Y616C gene product is a hypomorphic variant that exhibited oligomerization defects in yeast as well as in patient fibroblasts. Specifically, the formation of AFG3L2 Y616C complexes was impaired, both with itself and to a greater extent with paraplegin. This produced an early-onset clinical syndrome that combines the severe phenotypes of SPG7 and SCA28, in additional to other ''mitochondrial'' features such as oculomotor apraxia, extrapyramidal dysfunction, and myoclonic epilepsy. These findings expand the phenotype associated with AFG3L2 mutations and suggest that AFG3L2-related disease should be considered in the differential diagnosis of spastic ataxias.
Cell, 1998
Hereditary spastic paraplegia (HSP) is characterized by progressive weakness and spasticity of the lower limbs due to degeneration of corticospinal axons. We found that patients from a chromosome 16q24. 3-linked HSP family are homozygous for a 9.5 kb deletion involving a gene encoding a novel protein, named Paraplegin. Two additional Paraplegin mutations, both resulting in a frameshift, were found in a complicated and in a pure form of HSP. Paraplegin is highly homologous to the yeast mitochondrial ATPases, ...