title: Cofactor-dependent maturation of mammalian sulfite oxidase links two mitochondrial import pathways.
abstract: Sulfite oxidase (SO) catalyses the metabolic detoxification of sulfite to sulfate within the intermembrane space of mitochondria. The enzyme follows a complex maturation pathway, including mitochondrial transport and processing, integration of two prosthetic groups, molybdenum cofactor (Moco) and heme, as well as homodimerisation. We have identified the sequential and cofactor-dependent maturation steps of SO. The N-terminal bipartite targeting signal of SO was required but not sufficient for mitochondrial localization. In the absence of Moco, most of the SO, although processed by the inner membrane peptidase of mitochondria, was found in the cytosol. Moco binding was required to induce mitochondrial trapping and retention, thus ensuring unidirectional translocation of SO. In the absence of the N-terminal targeting sequence, SO assembled in the cytosol, suggesting an important function for the leader sequence in preventing premature cofactor binding. In vivo, heme binding and dimerisation did not occur in the absence of Moco and only occurred after Moco integration. In conclusion, the identified molecular hierarchy of SO maturation represents a novel link between the canonical presequence pathway and folding-trap mechanisms of mitochondrial import.
authors.affiliation: Institut für Biochemie, Department Chemie und Zentrum für Molekulare Medizin Köln, Universität zu Köln, Germany.
authors.forename: Julian M
authors.initials: JM
authors.lastname: Klein
authors.forename: Guenter
authors.initials: G
authors.lastname: Schwarz
mesh_terms: D000818:Animals; D003067:Coenzymes / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology / Q000378:metabolism; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006418:Heme / Q000378:metabolism*; D006801:Humans; D053858:Metabolic Networks and Pathways; D008667:Metalloproteins / Q000378:metabolism*; D051379:Mice; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism; D051336:Mitochondrial Membranes / Q000201:enzymology / Q000378:metabolism; D000090006:Molybdenum Cofactors; D011485:Protein Binding; D021381:Protein Transport; D011621:Pteridines / Q000378:metabolism*; D050876:Sulfite Oxidase / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D003067:Coenzymes; D006418:Heme; D008667:Metalloproteins; D000090006:Molybdenum Cofactors; D011621:Pteridines; D050876:Sulfite Oxidase; C022261:molybdopterin