Preprotein translocase of the outer mitochondrial membrane: reconstituted Tom40 forms a characteristic TOM pore.
Tom40 is the central pore-forming component of the translocase of the outer mitochondrial membrane (TOM complex). Different views exist about the secondary structure and electrophysiological characteristics of Tom40 from Saccharomyces cerevisiae and Neurospora crassa. We have directly compared expressed and renatured Tom40 from both species and find a high content of beta-structure in circular dichroism measurements in agreement with refined secondary structure predictions. The electrophysiological characterization of renatured Tom40 reveals the same characteristics as the purified TOM complex or mitochondrial outer membrane vesicles, with two exceptions. The total conductance of the TOM complex and outer membrane vesicles is twofold higher than the total conductance of renatured Tom40, consistent with the presence of two TOM pores. TOM complex and outer membrane vesicles possess a strongly enhanced sensitivity to a mitochondrial presequence compared to Tom40 alone, in agreement with the presence of several presequence binding sites in the TOM complex, suggesting a role of the non-channel Tom proteins in regulating channel activity.
Becker
Lars
L
Biophysik, Universität Osnabrück, FB Biologie/Chemie, D-49034 Osnabrück, Germany.
Bannwarth
Michael
M
Meisinger
Chris
C
Hill
Kerstin
K
Model
Kirstin
K
Krimmer
Thomas
T
Casadio
Rita
R
Truscott
Kaye N
KN
Schulz
Georg E
GE
Pfanner
Nikolaus
N
Wagner
Richard
R
D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000502:physiology; D004594:Electrophysiology; D005656:Fungal Proteins / Q000737:chemistry / Q000502:physiology; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000502:physiology; D033681:Mitochondrial Membrane Transport Proteins; D051336:Mitochondrial Membranes; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins / Q000737:chemistry* / Q000502:physiology; D009492:Neurospora crassa / Q000737:chemistry; D017433:Protein Structure, Secondary; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000502:physiology
D002352:Carrier Proteins; D005656:Fungal Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D029701:Saccharomyces cerevisiae Proteins; C066555:Tom40 protein, S cerevisiae