Protein translocation through Tom40: kinetics of peptide release.
Mitochondrial proteins are almost exclusively imported into mitochondria from the cytosol in an unfolded or partially folded conformation. Regardless of whether they are destined for the outer or inner membrane, the intermembrane space, or the matrix, proteins begin the importation process by crossing the mitochondrial outer membrane via a specialized protein import machinery whose main component is the Tom40 channel. High-resolution ion conductance measurements through the Tom40 channel in the presence of the mitochondrial presequence peptide pF(1)β revealed the kinetics of peptide binding. Here we show that the rates for association k(on) and dissociation k(off) strongly depend on the applied transmembrane voltage. Both kinetic constants increase with an increase in the applied voltage. The increase of k(off) with voltage provides strong evidence of peptide translocation. This allows us to distinguish quantitatively between substrate blocking and permeation.
School of Engineering and Science, Jacobs University Bremen, Bremen, Germany.
Kozhinjampara R
KR
Mahendran
Mercedes
M
Romero-Ruiz
Andrea
A
Schlösinger
Mathias
M
Winterhalter
Stephan
S
Nussberger
D001665:Binding Sites; D003198:Computer Simulation; D007700:Kinetics; D026901:Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D008956:Models, Chemical; D008958:Models, Molecular; D009038:Motion; D010455:Peptides / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D021381:Protein Transport
D026901:Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D010455:Peptides; C000707766:Tomm40 protein, rat