A large Ca2+-dependent channel formed by recombinant ADP/ATP carrier from Neurospora crassa resembles the mitochondrial permeability transition pore.
Strong support for the central role of the ADP/ATP carrier (AAC) in the mitochondrial permeability transition (mPT) is provided by the single-channel current measurements in patch-clamp experiments with the isolated reconstituted AAC. In previous work [Brustovetsky, N., and Klingenberg, M. (1996) Biochemistry 35, 8483-8488], this technique was applied to the AAC isolated from bovine heart mitochondria. Here we used recombinant AAC (rAAC) from Neurospora crassa expressed in E. coli, since AAC from mammalian sources cannot be expresssed in E. coli. The rAAC is free from residual mitochondrial components which might associate with the AAC in preparation from bovine heart. Ca(2+)-dependent channels with up to 600 pS are obtained, which are gated at >150 mV. The channel corresponds to a preferential matrix-outside orientation of rAAC in the patch membrane as shown with carboxyatractylate and a polar gating asymmetry. The channel is inhibited by ADP and bongkrekate, not by carboxyatractylate. Cyclophilin, isolated from Neurospora crassa, suppresses the gating, thus increasing conductivity at high positive voltage. Cyclosporin A abolishes the cyclophilin effect. ADP does not eliminate the cyclophilin effect but produces fast large-amplitude flickering of the channel without a stable decrease of the channel conductance. Also the pro-oxidant tert-butyl hydroperoxide reversibly suppresses voltage gating of the channel. The results show that the AAC can be a conducting component of the mPT pore, exhibiting similar characteristics as the mPT pore (response to Ca(2+), BKA, ADP), with a cyclophilin and pro-oxidant-sensitive gating at high voltage.
Brustovetsky
Nickolay
N
Institute for Physiological Biochemistry, University of Munich, Schillerstrasse 44, 80336 Munich, Federal Republic of Germany. brous003@tc.umn.edu
Tropschug
Maximilian
M
Heimpel
Simone
S
Heidkämper
Doerthe
D
Klingenberg
Martin
M
D000818:Animals; D002118:Calcium / Q000502:physiology; D015220:Calcium Channels / Q000737:chemistry* / Q000235:genetics; D002417:Cattle; D021983:Cyclophilins / Q000494:pharmacology; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics; D015640:Ion Channel Gating / Q000187:drug effects; D007473:Ion Channels / Q000737:chemistry* / Q000235:genetics; D008929:Mitochondria, Heart / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics; D000226:Mitochondrial ADP, ATP Translocases / Q000737:chemistry* / Q000235:genetics; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D009492:Neurospora crassa; D018384:Oxidative Stress / Q000187:drug effects / Q000235:genetics; D018408:Patch-Clamp Techniques; D010539:Permeability / Q000187:drug effects; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics
D015220:Calcium Channels; D005656:Fungal Proteins; D007473:Ion Channels; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D011994:Recombinant Proteins; D000226:Mitochondrial ADP, ATP Translocases; D021983:Cyclophilins; D002118:Calcium