TOPOGRAPHY OF THE LEYDIG-CELL MITOCHONDRIAL PERIPHERAL-TYPE BENZODIAZEPINE RECEPTOR

Native MA-10 mouse Leydig tumor cell mitochondrial preparations were e xamined by transmission electron (TEM) and atomic force (AFM) microsco pic procedures in order to investigate the topography and organization of the peripheral-type benzodiazepine receptor (PBR). Mitochondria we re immunolabeled with an anti-PBR antiserum coupled to gold-labeled se condary antibodies. Results obtained indicate that the 18 000 MW PBR p rotein is organized in clusters of 4-6 molecules. Moreover, on many oc casions, the interrelationship among the PBR molecules was found to fa vor the formation of a single pore. Taking into account recent observa tions that the 18 000 MW PBR protein is functionally associated with t he pore forming 34 000 MW voltage-dependent anion channel (VDAC) these results suggest that (i) the mitochondrial PBR complex could function as a pore, thus allowing the translocation of cholesterol and other m olecules to the inner mitochondrial membrane, and (ii) the native rece ptor is a multimeric complex of an approximate 140 000 MW composed on an average of five 18 000 PBR subunits, one 34 000 VDAC subunit, and a ssociated lipids.