title: Construction and validation of an atomic model for bacterial TSPO from electron microscopy density, evolutionary constraints, and biochemical and biophysical data.
abstract: 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.
authors.affiliation: Centre de Biophysique Moléculaire (CNRS), Rue Charles Sadron, 45071 Orléans Cedex, France; Synchrotron SOLEIL, Division Expériences, Saint Aubin, B.P. 48, 91192 Gif-sur-Yvette Cedex, France. Electronic address: konrad.hinsen@cnrs-orleans.fr.
authors.forename: Konrad
authors.initials: K
authors.lastname: Hinsen
authors.affiliation: INSERM, UMR-S1134, 6 rue Alexandre Cabanel, Université Paris 7 Denis Diderot, F-75015 Paris, France; Université Paris Diderot, Sorbonne Paris Cité, Paris, France; Institut National de la Transfusion Sanguine (INTS), Paris, France; GR-Ex, Laboratoire d'Excellence, Paris, France; National Centre for Biological Sciences (NCBS), Tata Institute for Fundamental Research, GKVK Campus, Bangalore, Karnataka, India; Dynamique des Structures et des Interactions des des Macromolécules Biologiques, France. Electronic address: aurore.vaitinadapoule@inserm.fr.
authors.forename: Aurore
authors.initials: A
authors.lastname: Vaitinadapoule
authors.affiliation: INSERM, UMR-S1134, 6 rue Alexandre Cabanel, Université Paris 7 Denis Diderot, F-75015 Paris, France; Université Paris Diderot, Sorbonne Paris Cité, Paris, France; Institut National de la Transfusion Sanguine (INTS), Paris, France; GR-Ex, Laboratoire d'Excellence, Paris, France. Electronic address: mariano.ostuni@inserm.fr.
authors.forename: Mariano A
authors.initials: MA
authors.lastname: Ostuni
authors.affiliation: INSERM, UMR-S1134, 6 rue Alexandre Cabanel, Université Paris 7 Denis Diderot, F-75015 Paris, France; Université Paris Diderot, Sorbonne Paris Cité, Paris, France; Institut National de la Transfusion Sanguine (INTS), Paris, France; GR-Ex, Laboratoire d'Excellence, Paris, France; Dynamique des Structures et des Interactions des des Macromolécules Biologiques, France. Electronic address: catherine.etchebest@inserm.fr.
authors.forename: Catherine
authors.initials: C
authors.lastname: Etchebest
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, Laboratoire de Biomolécules (LBM), 4 Place Jussieu, F-75005 Paris, France; Ecole Normale Supérieure - PSL Research University, Département de Chimie, 24, rue Lhomond, 75005 Paris, France; CNRS, UMR 7203 LBM, F-75005 Paris, France. Electronic address: jean-jacques.lacapere@upmc.fr.
authors.forename: Jean-Jacques
authors.initials: JJ
authors.lastname: Lacapere
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry*; D002784:Cholesterol / Q000737:chemistry; D017124:Conserved Sequence; D020285:Cryoelectron Microscopy; D003460:Crystallization; D007546:Isoquinolines / Q000737:chemistry; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D011524:Protoporphyrins / Q000737:chemistry; D012242:Rhodobacter sphaeroides / Q000737:chemistry*; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D007546:Isoquinolines; D008024:Ligands; D011524:Protoporphyrins; D002784:Cholesterol; C037850:PK 11195
keywords: Membrane protein; Translocase 18kDa; Transporter