• Isolation, characterisation and molecular imaging of a high-molecular-weight insect biliprotein, a member of the hexameric arylphorin protein family.

      Kayser, Hartmut; Mann, Karlheinz; Machaidze, Gia; Nimtz, Manfred; Ringler, Philippe; Müller, Shirley A; Aebi, Ueli; Institut für Allgemeine Zoologie und Endokrinologie, Universität Ulm, Germany. hartmut.kayser@uni-ulm.de (2009-05-29)
      The abundant blue hemolymph protein of the last instar larvae of the moth Cerura vinula was purified and characterized by protein-analytical, spectroscopic and electron microscopic methods. Amino acid sequences obtained from a large number of cleavage peptides revealed a high level of similarity of the blue protein with arylphorins from a number of other moth species. In particular, there is a high abundance of the aromatic amino acids tyrosine and phenylalanine amounting to about 19% of total amino acids and a low content of methionine (0.8%) in the Cerura protein. The mass of the native protein complex was studied by size-exclusion chromatography, analytical ultracentrifugation, dynamic light scattering and scanning transmission electron microscopy and found to be around 500 kDa. Denaturating gel electrophoresis and mass spectrometry suggested the presence of two proteins with masses of about 85 kDa. The native Cerura protein is, therefore, a hexameric complex of two different subunits of similar size, as is known for arylphorins. The protein was further characterized as a weakly acidic (pI approximately 5.5) glycoprotein containing mannose, glucose and N-acetylglucosamine in an approximate ratio of 10:1:1. The structure proposed for the most abundant oligosaccharide of the Cerura arylphorin was the same as already identified in arylphorins from other moths. The intense blue colour of the Cerura protein is due to non-covalent association with a bilin of novel structure at an estimated protein subunit-to-ligand ratio of 3:1. Transmission electron microscopy of the biliprotein showed single particles of cylindrical shape measuring about 13 nm in diameter and 9 nm in height. A small fraction of particles of the same diameter but half the height was likely a trimeric arylphorin dissociation intermediate. Preliminary three-dimensional reconstruction based on averaged transmission electron microscopy projections of the individual particles revealed a double-trimeric structure for the hexameric Cerura biliprotein complex, suggesting it to be a dimer of trimers.
    • Myelin 2',3'-cyclic nucleotide 3'-phosphodiesterase: active-site ligand binding and molecular conformation.

      Myllykoski, Matti; Raasakka, Arne; Han, Huijong; Kursula, Petri; Department of Biochemistry and Biocenter Oulu, University of Oulu, Oulu, Finland. (2012)
      The 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) is a highly abundant membrane-associated enzyme in the myelin sheath of the vertebrate nervous system. CNPase is a member of the 2H phosphoesterase family and catalyzes the formation of 2'-nucleotide products from 2',3'-cyclic substrates; however, its physiological substrate and function remain unknown. It is likely that CNPase participates in RNA metabolism in the myelinating cell. We solved crystal structures of the phosphodiesterase domain of mouse CNPase, showing the binding mode of nucleotide ligands in the active site. The binding mode of the product 2'-AMP provides a detailed view of the reaction mechanism. Comparisons of CNPase crystal structures highlight flexible loops, which could play roles in substrate recognition; large differences in the active-site vicinity are observed when comparing more distant members of the 2H family. We also studied the full-length CNPase, showing its N-terminal domain is involved in RNA binding and dimerization. Our results provide a detailed picture of the CNPase active site during its catalytic cycle, and suggest a specific function for the previously uncharacterized N-terminal domain.
    • Structure of the effector-binding domain of the LysR-type transcription factor RovM from Yersinia pseudotuberculosis.

      Quade, Nick; Dieckmann, Marieke; Haffke, Matthias; Heroven, Ann Kathrin; Dersch, Petra; Heinz, Dirk W; Department of Molecular Structural Biology, Helmholtz Centre for Infection Research, D-38124 Braunschweig, Germany. (2011-02)
      In enteropathogenic Yersinia, the expression of several early-phase virulence factors such as invasin is tightly regulated in response to environmental cues. The responsible regulatory network is complex, involving several regulatory RNAs and proteins such as the LysR-type transcription regulator (LTTR) RovM. In this study, the crystal structure of the effector-binding domain (EBD) of RovM, the first LTTR protein described as being involved in virulence regulation, was determined at a resolution of 2.4 Å. Size-exclusion chromatography and comparison with structures of full-length LTTRs show that RovM is most likely to adopt a tetrameric arrangement with two distant DNA-binding domains (DBDs), causing the DNA to bend around it. Additionally, a cavity was detected in RovM which could bind small inducer molecules.