title: Biogenesis of the preprotein translocase of the outer mitochondrial membrane: protein kinase A phosphorylates the precursor of Tom40 and impairs its import.
abstract: The preprotein translocase of the outer mitochondrial membrane (TOM) functions as the main entry gate for the import of nuclear-encoded proteins into mitochondria. The major subunits of the TOM complex are the three receptors Tom20, Tom22, and Tom70 and the central channel-forming protein Tom40. Cytosolic kinases have been shown to regulate the biogenesis and activity of the Tom receptors. Casein kinase 2 stimulates the biogenesis of Tom22 and Tom20, whereas protein kinase A (PKA) impairs the receptor function of Tom70. Here we report that PKA exerts an inhibitory effect on the biogenesis of the β-barrel protein Tom40. Tom40 is synthesized as precursor on cytosolic ribosomes and subsequently imported into mitochondria. We show that PKA phosphorylates the precursor of Tom40. The phosphorylated Tom40 precursor is impaired in import into mitochondria, whereas the nonphosphorylated precursor is efficiently imported. We conclude that PKA plays a dual role in the regulation of the TOM complex. Phosphorylation by PKA not only impairs the receptor activity of Tom70, but it also inhibits the biogenesis of the channel protein Tom40.
authors.affiliation: Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, 79104 Freiburg, Germany.
authors.forename: Sanjana
authors.initials: S
authors.lastname: Rao
authors.forename: Oliver
authors.initials: O
authors.lastname: Schmidt
authors.forename: Angelika B
authors.initials: AB
authors.lastname: Harbauer
authors.forename: Birgit
authors.initials: B
authors.lastname: Schönfisch
authors.forename: Bernard
authors.initials: B
authors.lastname: Guiard
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Pfanner
authors.forename: Chris
authors.initials: C
authors.lastname: Meisinger
mesh_terms: D002352:Carrier Proteins / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000201:enzymology / Q000378:metabolism*; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D010766:Phosphorylation; D011498:Protein Precursors / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D011498:Protein Precursors; D029701:Saccharomyces cerevisiae Proteins; C066555:Tom40 protein, S cerevisiae; D017868:Cyclic AMP-Dependent Protein Kinases