Role of Tim17 Transmembrane Regions in Regulating the Architecture of Presequence Translocase and Mitochondrial DNA Stability

Mol Cell Biol. 2017 Mar 1;37(6):e00491-16. doi: 10.1128/MCB.00491-16. Print 2017 Mar 15.

Abstract

Mitochondrial life cycle and protein import are intricate cellular processes, which require precise coordination between the transport machineries of outer and inner mitochondrial membranes. Presequence translocase performs the indispensable function of translocating preproteins having N-terminal targeting sequences across the inner membrane. Tim23 forms the core of the voltage-gated import channel, while Tim17 is presumed to maintain the stoichiometry of the translocase. However, mechanistic insights into how Tim17 coordinates these regulatory events within the complex remained elusive. We demonstrate that Tim17 harbors conserved G/AXXXG/A motifs within its transmembrane regions and plays an imperative role in the translocase assembly through interaction with Tim23. Tandem motifs are highly essential, as most of the amino acid substitutions lead to nonviability due to the complete destabilization of the TIM23 channel. Importantly, Tim17 transmembrane regions regulate the dynamic assembly of translocase to form either the TIM23 (PAM)-complex or TIM23 (SORT)-complex by recruiting the presequence translocase-associated motor (PAM) machinery or Tim21, respectively. To a greater significance, tim17 mutants displayed mitochondrial DNA (mtDNA) instability, membrane potential loss, and defective import, resulting in organellar dysfunction. We conclude that the integrity of Tim17 transmembrane regions is critical for mitochondrial function and protein turnover.

Keywords: membrane potential; mitochondria; mtDNA stability; preprotein import; presequence translocase.

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Sequence
  • Conserved Sequence
  • DNA, Mitochondrial / metabolism*
  • Membrane Potentials
  • Mitochondria / metabolism*
  • Mitochondrial Membrane Transport Proteins / chemistry*
  • Mitochondrial Membrane Transport Proteins / metabolism*
  • Mitochondrial Membranes / metabolism
  • Mutation / genetics
  • Phenotype
  • Protein Sorting Signals
  • Protein Stability
  • Protein Transport
  • Reactive Oxygen Species / metabolism
  • Saccharomyces cerevisiae / cytology
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae Proteins / chemistry*
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Structure-Activity Relationship

Substances

  • DNA, Mitochondrial
  • Mitochondrial Membrane Transport Proteins
  • Protein Sorting Signals
  • Reactive Oxygen Species
  • Saccharomyces cerevisiae Proteins
  • TIM17 protein, S cerevisiae