TitleConstruction and validation of an atomic model for bacterial TSPO from electron microscopy density, evolutionary constraints, and biochemical and biophysical data.
Publication TypeJournal Article
Year of Publication2015
AuthorsHinsen K, Vaitinadapoule A, Ostuni MA, Etchebest C, Lacapere J-J
JournalBiochim Biophys Acta
Date Published2015 Feb
KeywordsAmino Acid Sequence, Bacterial Proteins, Binding Sites, Carrier Proteins, Cholesterol, Conserved Sequence, Cryoelectron Microscopy, Crystallization, Isoquinolines, Ligands, Models, Molecular, Molecular Sequence Data, Protein Binding, Protein Multimerization, Protein Structure, Secondary, Protoporphyrins, Rhodobacter sphaeroides, Sequence Alignment

The 18 kDa protein TSPO is a highly conserved transmembrane protein found in bacteria, yeast, animals and plants. TSPO is involved in a wide range of physiological functions, among which the transport of several molecules. The atomic structure of monomeric ligand-bound mouse TSPO in detergent has been published recently. A previously published low-resolution structure of Rhodobacter sphaeroides TSPO, obtained from tubular crystals with lipids and observed in cryo-electron microscopy, revealed an oligomeric structure without any ligand. We analyze this electron microscopy density in view of available biochemical and biophysical data, building a matching atomic model for the monomer and then the entire crystal. We compare its intra- and inter-molecular contacts with those predicted by amino acid covariation in TSPO proteins from evolutionary sequence analysis. The arrangement of the five transmembrane helices in a monomer of our model is different from that observed for the mouse TSPO. We analyze possible ligand binding sites for protoporphyrin, for the high-affinity ligand PK 11195, and for cholesterol in TSPO monomers and/or oligomers, and we discuss possible functional implications.

Alternate JournalBiochim. Biophys. Acta
PubMed ID25450341