Steroidogenic acute regulatory protein and peripheral-type benzodiazepine receptor associate at the mitochondrial membrane.

Steroidogenic acute regulatory protein (StAR) and peripheral-type benzodiaz epine receptor (PBR) have both been implicated in the transport of choleste rol across mitochondrial membranes in steroidogenic cells. Therefore, we hy pothesized that StAR and PER were associated in this process. To test this hypothesis, we measured fluorescence energy transfer (FET) between these pr oteins by fusing enhanced green fluorescent protein (GFP, donor fluorophore ) and yellow fluorescent protein (YFP, acceptor fluorophore) to the C-tamin us of ovine StAR (37GFP) and ovine PER (PBRYFP), respectively. These intrin sically fluorescent proteins were stably transfected into Cos-7 cells and d etermined to be biologically active. For FET to occur the appropriate fluor escent molecules need to be < 100 <Angstrom> from each other. We observed 2 2.0 +/- 0.9 % energy transfer efficiency for 37GFP and PBRYFP, a 4.9 fold i ncrease above non-specific energy transfer between free GFP and PBRYFP (p < .0001). Thus, it appears that StAR and PER are closely associated in mitoc hondrial membranes and that these molecules may interact in the transportat ion of cholesterol.