Two distinct membrane potential-dependent steps drive mitochondrial matrix protein translocation

J Cell Biol. 2017 Jan 2;216(1):83-92. doi: 10.1083/jcb.201607066. Epub 2016 Dec 23.

Abstract

Two driving forces energize precursor translocation across the inner mitochondrial membrane. Although the membrane potential (Δψ) is considered to drive translocation of positively charged presequences through the TIM23 complex (presequence translocase), the activity of the Hsp70-powered import motor is crucial for the translocation of the mature protein portion into the matrix. In this study, we show that mitochondrial matrix proteins display surprisingly different dependencies on the Δψ. However, a precursor's hypersensitivity to a reduction of the Δψ is not linked to the respective presequence, but rather to the mature portion of the polypeptide chain. The presequence translocase constituent Pam17 is specifically recruited by the receptor Tim50 to promote the transport of hypersensitive precursors into the matrix. Our analyses show that two distinct Δψ-driven translocation steps energize precursor passage across the inner mitochondrial membrane. The Δψ- and Pam17-dependent import step identified in this study is positioned between the two known energy-dependent steps: Δψ-driven presequence translocation and adenosine triphosphate-driven import motor activity.

MeSH terms

  • Adenosine Triphosphate / metabolism
  • Genotype
  • Hydrolysis
  • Membrane Potential, Mitochondrial*
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Mitochondria / metabolism*
  • Mitochondrial Membrane Transport Proteins / genetics
  • Mitochondrial Membrane Transport Proteins / metabolism*
  • Mitochondrial Membranes / metabolism*
  • Mitochondrial Precursor Protein Import Complex Proteins
  • Mutation
  • Phenotype
  • Protein Precursors / genetics
  • Protein Precursors / metabolism*
  • Protein Transport
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Time Factors

Substances

  • Membrane Proteins
  • Mitochondrial Membrane Transport Proteins
  • Mitochondrial Precursor Protein Import Complex Proteins
  • Pam17 protein, S cerevisiae
  • Protein Precursors
  • Saccharomyces cerevisiae Proteins
  • TIM50 protein, S cerevisiae
  • Adenosine Triphosphate