Distorted octahedral coordination of tungstate in a subfamily of specific binding proteins

Bacteria and archaea import molybdenum and tungsten from the environment in the form of the oxyanions molybdate (MoO4 2−) and tungstate (WO4 2−). These substrates are captured by an external, high-affinity binding protein, and delivered to ATP binding cassette transporters, which move them across the cell membrane. We have recently reported a crystal structure of the molybdate/tungstate binding protein ModA/WtpA from Archaeoglobus fulgidus, which revealed an octahedrally coordinated central metal atom. By contrast, the previously determined structures of three bacterial homologs showed tetracoordinate molybdenum and tungsten atoms in their binding pockets. Until then, coordination numbers above four had only been found for molybdenum/tungsten in metalloenzymes where these metal atoms are part of the catalytic cofactors and coordinated by mostly non-oxygen ligands. We now report a high-resolution structure of A. fulgidus ModA/WtpA, as well as crystal structures of four additional homologs, all bound to tungstate. These crystal structures match X-ray absorption spectroscopy measurements from soluble, tungstate-bound protein, and reveal the details of the distorted octahedral coordination. Our results demonstrate that the distorted octahedral geometry is not an exclusive feature of the A. fulgidus protein, and suggest distinct binding modes of the binding proteins from archaea and bacteri

Decoding Corticotropin-Releasing Factor Receptor Type 1 Crystal Structures.

The structural analysis of class B G protein-coupled receptors (GPCR), cell surface proteins responding to peptide hormones, has until recently been restricted to the extracellular domain (ECD). Corticotropin-releasing factor receptor type 1 (CRF1R) is a class B receptor mediating stress response and also considered a drug target for depression and anxiety. Here we report the crystal structure of the transmembrane domain of human CRF1R in complex with the small-molecule antagonist CP-376395 in a hexagonal setting with translational non-crystallographic symmetry. Molecular dynamics and metadynamics simulations on this novel structure and the existing TMD structure for CRF1R provides insight as to how the small molecule ligand gains access to the induced-fit allosteric binding site with implications for the observed selectivity against CRF2R. Furthermore, molecular dynamics simulations performed using a full-length receptor model point to key interactions between the ECD and extracellular loop 3 of the TMD providing insight into the full inactive state of multidomain class B GPCRs.This is the accepted manuscript. It is currently embargoed pending publication

Distorted octahedral coordination of tungstate in a subfamily of specific binding proteins

Bacteria and archaea import molybdenum andtungsten from the environment in the form of theoxyanions molybdate (MoO42-) and tungstate (WO42-).These substrates are captured by an external, high-affinitybinding protein, and delivered to ATP binding cassettetransporters, which move them across the cell membrane.We have recently reported a crystal structure of themolybdate/tungstate binding protein ModA/WtpA fromArchaeoglobus fulgidus, which revealed an octahedrallycoordinated central metal atom. By contrast, the previouslydetermined structures of three bacterial homologs showedtetracoordinate molybdenum and tungsten atoms in theirbinding pockets. Until then, coordination numbers abovefour had only been found for molybdenum/tungsten inmetalloenzymes where these metal atoms are part of thecatalytic cofactors and coordinated by mostly non-oxygenligands. We now report a high-resolution structure ofA. fulgidus ModA/WtpA, as well as crystal structures offour additional homologs, all bound to tungstate. Thesecrystal structures match X-ray absorption spectroscopymeasurements from soluble, tungstate-bound protein, andreveal the details of the distorted octahedral coordination.Our results demonstrate that the distorted octahedralgeometry is not an exclusive feature of the A. fulgidusprotein, and suggest distinct binding modes of the bindingproteins from archaea and bacteria

Anion binding in biological systems

Contains fulltext : 74654.pdf (postprint version ) (Open Access)6 p

Structure of the adenosine A 2A receptor in complex with ZM241385 and the xanthines XAC and caffeine

Methylxanthines, including caffeine and theophylline are among the most widely consumed stimulant drugs in the world. These effects are mediated primarily via blockade of adenosine receptors. Xanthine analogues with improved properties have been developed as potential treatments for diseases such as Parkinson’s disease. Here we report the structures of a thermostabilised adenosine A(2A) receptor in complex with the xanthines xanthine amine congener and caffeine, as well as the A(2A) selective inverse agonist ZM241385. The receptor is crystallised in the inactive state conformation as defined by the presence of a salt bridge known as the ionic lock. The complete third intracellular loop, responsible for G protein coupling, is visible consisting of extended helices 5 and 6. The structures provide new insight into the features which define the ligand binding pocket of the adenosine receptor for ligands of diverse chemotypes as well as the cytoplasmic regions which interact with signal transduction proteins