Role of Pam16's degenerate J domain in protein import across the mitochondrial inner membrane

Proc Natl Acad Sci U S A. 2005 Aug 30;102(35):12419-24. doi: 10.1073/pnas.0505969102. Epub 2005 Aug 16.


Translocation of proteins across the mitochondrial inner membrane is an essential process requiring an import motor having mitochondrial Hsp70 (mtHsp70) at its core. The J protein partner of mtHsp70, Pam18, is an integral part of this motor, serving to stimulate the ATPase activity of mtHsp70. Pam16, an essential protein having an inactive J domain that is unable to stimulate mtHsp70's ATPase activity, forms a heterodimer with Pam18, but its function is unknown. We set out to test the importance of three properties of Pam16: (i) a stable interaction between Pam16 and Pam18, (ii) the inability of Pam16's degenerate J domain to stimulate Ssc1's ATPase domain, and (iii) the innately lower stimulatory activity of the Pam16:Pam18 heterodimer, compared to Pam18 alone. Neither substantial reduction in the ability of Pam18 to stimulate Ssc1's ATPase activity, nor the presence of an active J domain in Pam16, had deleterious effects on cell growth, indicating the lack of importance of two of these biochemical properties. However, a stable interaction between Pam16's degenerate J domain and Pam18's J domain was found to be critical for function. Alterations that destabilized the Pam16:Pam18 heterodimer had deleterious effects on cell growth and mitochondrial protein import; intragenic suppressors that restored robust growth also restored heterodimer stability. Our results support the idea that Pam16's J-like domain strongly interacts with Pam18's J domain, leading to a productive interaction of Pam18 with mtHsp70 at the import channel.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Biological Transport, Active
  • Calcium-Transporting ATPases / chemistry
  • Calcium-Transporting ATPases / genetics
  • Calcium-Transporting ATPases / metabolism
  • Dimerization
  • Intracellular Membranes / metabolism
  • Membrane Transport Proteins / chemistry*
  • Membrane Transport Proteins / genetics
  • Membrane Transport Proteins / metabolism*
  • Mitochondria / metabolism
  • Mitochondrial Membrane Transport Proteins
  • Mitochondrial Proteins / chemistry*
  • Mitochondrial Proteins / genetics
  • Mitochondrial Proteins / metabolism*
  • Models, Molecular
  • Molecular Chaperones / chemistry
  • Molecular Chaperones / genetics
  • Molecular Chaperones / metabolism
  • Molecular Motor Proteins / genetics
  • Molecular Motor Proteins / metabolism
  • Mutagenesis, Site-Directed
  • Mutation
  • Phenotype
  • Protein Structure, Quaternary
  • Protein Structure, Tertiary
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae / metabolism
  • Saccharomyces cerevisiae Proteins / chemistry*
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Temperature


  • Membrane Transport Proteins
  • Mitochondrial Membrane Transport Proteins
  • Mitochondrial Proteins
  • Molecular Chaperones
  • Molecular Motor Proteins
  • PAM18 J protein, S cerevisiae
  • Pam16 protein, S cerevisiae
  • Recombinant Fusion Proteins
  • SSC1 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Calcium-Transporting ATPases