PERIPHERAL-TYPE BENZODIAZEPINE RECEPTOR FUNCTION IN CHOLESTEROL TRANSPORT - IDENTIFICATION OF A PUTATIVE CHOLESTEROL RECOGNITION INTERACTION AMINO-ACID-SEQUENCE AND CONSENSUS PATTERNS/

In steroid-synthesizing cells, like the MA-10 mouse tumor Leydig cells , the peripheral-type benzodiazepine receptor (PBR) is an outer mitoch ondrial membrane protein involved in the regulation of cholesterol tra nsport from the outer to the inner mitochondrial membrane, the rate-de termining step in steroid biosynthesis. Expression of PER in Escherich ia coli DE3 cells, which have no PER, no cholesterol, acid do not make steroids, induced the ability to take up cholesterol in a time-depend ent, temperature-sensitive, and energy-independent manner. These cells took up no other steroids tested. Addition of the high affinity PER l igand PK 11195 to cholesterol-loaded membranes, obtained from cells tr ansfected with PER, resulted in the release of the uptaken cholesterol . Expression in DE3 cells of mutant PBRs demonstrated that deletions i n the cytoplasmic carboxy-terminus dramatically reduced the cholestero l uptake function of PER, although it retained full capacity to bind P K 11195. Site-directed mutagenesis in the carboxy-terminal region of P ER demonstrated that bacteria expressing the mutant PER proteins PBR(Y 153S) and PBR(R156L) do not accumulate cholesterol, suggesting that am ino acids Y153 and R156 are involved in the interaction of the recepto r with cholesterol. Considering these results, we postulate the existe nce of a common cholesterol recognition/interaction amino acid consens us pattern (-L/V-(X)(1-5)-Y-(X)(1-5)-R/K-). Indeed, we found this amin o acid consensus pattern in all proteins shown to interact with choles terol. In conclusion, these data suggest that the expression of PER co nfers the ability to take up and release, upon ligand activation, chol esterol. Considering the widespread occurrence of this protein and its tissue and cell specific subcellular localization, these results sugg est a more general role of PER in intracellular cholesterol transport and compartmentalization.