Journal Article

A Novel <i>Arabidopsis thaliana</i> Protein is a Functional Peripheral-Type Benzodiazepine Receptor

Peter Lindemann, Antje Koch, Babett Degenhardt, Gerd Hause, Bernhard Grimm and Vassilios Papadopoulos

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 45, issue 6, pages 723-733
Published in print June 2004 | ISSN: 0032-0781
Published online June 2004 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pch088
A Novel Arabidopsis thaliana Protein is a Functional Peripheral-Type Benzodiazepine Receptor

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A key element in the regulation of mammalian steroid biosynthesis is the 18 kDa peripheral-type benzodiazepine receptor (PBR), which mediates mitochondrial cholesterol import. PBR also possess an affinity to the tetrapyrrole metabolite protoporphyrin. The bacterial homolog to the mammalian PBR, the Rhodobacter TspO (CrtK) protein, was shown to be involved in the bacterial tetrapyrrole metabolism. Looking for a similar mitochondrial import mechanism in plants, protein sequences from Arabidopsis and several other plants were found with significant similarities to the mammalian PBR and to the Rhodobacter TspO protein. A PBR-homologous Arabidopsis sequence was cloned and expressed in E. coli. The recombinant gene product showed specific high affinity benzodiazepine ligand binding. Moreover, the protein applied to E. coli protoplasts caused an equal benzodiazepine-stimulated uptake of cholesterol and protoporphyrin IX. These results suggest that the PBR like protein is involved in steroid import and is directing protoporphyrinogen IX to the mitochondrial site of protoheme formation.

Keywords: Keywords: Biosynthesis — Steroid — Tetrapyrrole — Transport.; Abbreviations: ADC, adenine nucleotide carrier; BAC, bacterial artificial chromosome; P450scc, cytochrome P450 cholesterol side chain cleavage; PBR, peripheral-type benzodiazepine receptor; PEM’s, proembryogenic masses; PK 11195, 1-(2-chlorophenyl)-N-methyl-(1-methylpropyl)-3-isoquinoline carboxamide; PPO, 2,5-diphenyloxazole; Ro5-4864, 4′-chlorodiazepam, 7-chloro-5-(4-chlorophenyl)-1,3-dihydro-1-methyl-2H-1,4-benzodiazepin-2-one; TEM, transmission electron microscopy; VDAC, voltage-dependent anion carrier.

Journal Article.  7192 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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