title: Mitochondrial matrix proteostasis is linked to hereditary paraganglioma: LON-mediated turnover of the human flavinylation factor SDH5 is regulated by its interaction with SDHA.
abstract: Mutations in succinate dehydrogenase (SDH) subunits and assembly factors cause a range of clinical conditions. One such condition, hereditary paraganglioma 2 (PGL2), is caused by a G78R mutation in the assembly factor SDH5. Although SDH5(G78R) is deficient in its ability to promote SDHA flavinylation, it has remained unclear whether impairment to its import, structure, or stability contributes to its loss of function. Using import-chase analysis in human mitochondria isolated from HeLa cells, we found that the import and maturation of human SDH5(G78R) was normal, while its stability was reduced significantly, with ~25% of the protein remaining after 180 min compared to ~85% for the wild-type protein. Notably, the metabolic stability of SDH5(G78R) was restored to wild-type levels by depleting mitochondrial LON (LONM). Degradation of SDH5(G78R) by LONM was confirmed in vitro; however, in contrast to the in organello analysis, wild-type SDH5 was also rapidly degraded by LONM. SDH5 instability was confirmed in SDHA-depleted mitochondria. Blue native PAGE showed that imported SDH5(G78R) formed a transient complex with SDHA; however, this complex was stabilized in LONM depleted mitochondria. These data demonstrate that SDH5 is protected from LONM-mediated degradation in mitochondria by its stable interaction with SDHA, a state that is dysregulated in PGL2.
authors.affiliation: 2Department of Biochemistry, La Trobe Institute for Molecular Science, La Trobe University, Melbourne 3086, Australia. K.N.T., k.truscott@latrobe.edu.au.
authors.forename: Ayenachew
authors.initials: A
authors.lastname: Bezawork-Geleta
authors.forename: Tamanna
authors.initials: T
authors.lastname: Saiyed
authors.forename: David A
authors.initials: DA
authors.lastname: Dougan
authors.forename: Kaye N
authors.initials: KN
authors.lastname: Truscott
mesh_terms: D042963:Electron Transport Complex II / Q000235:genetics / Q000378:metabolism*; D004795:Enzyme Stability / Q000235:genetics; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D010235:Paraganglioma / Q000235:genetics / Q000378:metabolism*; D049070:Protease La / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D057165:Proteostasis Deficiencies / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D024101:Mitochondrial Proteins; D021122:Protein Subunits; C543341:SDHAF2 protein, human; D005182:Flavin-Adenine Dinucleotide; D042963:Electron Transport Complex II; C511268:SDHA protein, human; D049070:Protease La
keywords: AAA+ protease; assembly factor; organelle; protein degradation; succinate dehydrogenase