Domain Structure of the Selenocysteine-specific Translation Factor SelB in Prokaryotes

Translation factor SelB is the key component for the specific decoding of UGA codons with selenocysteine at the ribosome. SelB binds selenocysteyl-tRNASec, guanine nucleotides and a secondary structure of the selenoprotein mRNA following the UGA at the 3' side. A comparison of the amino acid sequences of SelB species from E. coli,Desulfomicrobium baculatum, Clostridium thermoaceticum and Haemophilus influenzae showed that the proteins consist of at least four structural domains from which the Nterminal three are well conserved and share homology with elongation factor Tu whereas the C-terminal one is more variable and displays no similarity to any protein known. With the aid of the coordinates of EF-Tu the N-terminal part has been modelled into a 3D structure which exhibits intriguing features concerning its interaction with guanine nucleotides and other components of the translational apparatus. Cloning and expression of fragments of SelB and biochemical analysis of the purified truncated proteins showed that the C-terminal 19 kDa protein fragment is able to specifically bind to the selenoprotein mRNA. SelB, thus, is a translation factor functionally homologous to EF-Tu hooked up to the mRNA with its C-terminal end. The formation by SelB of a quaternary complex in vivo has been proven by overexpression of truncated genes of SelB and by demonstration that fragments comprising the mRNA or the tRNA binding domain inhibit selenocysteine insertion

Three-dimensional structures of virulence proteins of Legionella establish targets for new antibacterials

Legionella pneumophila,the causative agent of Legionnaires' disease,has been recognized as a major health problem responsible for an estimated number of 15 000-30 000 cases of severe pneumonia per year in Germany alone.Despite of the high clinical relevance,many aspects of the intracellular life cycle of Legionella,especially details on interactions with host cells,are not well understood.Structural information on virulence proteins helps unravel basal pathogenicity mechanisms and is a prerequisite for the rational development of effective drug molecules.Here we discuss structures of three important virulence proteins of Legionella that have been determined in our laboratory.The structure of the macrophage infectivity potentiator(Mip) protein of Legionella pneumophila is the first of a novel subgroup within the family of FK506-binding protein(FKBP) peptidyl-prolyl cis/trans isomerases.On the basis of the Mip structure,promising antibacterial agents are being designed.Recently,structures of two equally exciting Legionella proteins have been reported.The ferrous iron transport protein FeoB is a transmembrane protein responsible for Fe2+ aquisition after entry of the pathogen into the host cell.The structure of the cytoplasmic domain of FeoB provides insights into the family of prokaryotic G proteins and allows a detailed comparison with structures of related FeoBs.Furthermore,the characterization of DegQ,a periplasmatic chaperone-protease involved in protein quality control represents an intriguing example of how enzymatic activity is regulated by oligomerization as well as by an intrinsic loop activation cascade,depending on subtle conformational rearrangements.

Crystal structure of the C-terminal fragment of NS1 protein from yellow fever virus

Dear Editor,Yellow fever(YF),a mosquito-borne flavivirus disease,is endemic in tropical areas of Africa and Central and South America.YF is transmitted via the bite of infected Aedes aegypti or Haemogogus mosquitoes and mainly affects humans and nonhuman primates.The clinical course of infection in humans shows a wide spectrum of severity including no symptoms,mild illness,and severe disease including

Structural and mutational analysis of the interaction between the Middle-East respiratory syndrome coronavirus (MERS-CoV) papain-like protease and human ubiquitin

The papain-like protease(PL^(pro)) of Middle-East respiratory syndrome coronavirus(MERS-CoV) has proteolytic,deubiquitinating,and de ISGylating activities.The latter two are involved in the suppression of the antiviral innate immune response of the host cell.To contribute to an understanding of this process,we present here the X-ray crystal structure of a complex between MERS-CoV PL^(pro) and human ubiquitin(Ub) that is devoid of any covalent linkage between the two proteins.Five regions of the PL^(pro) bind to two areas of the Ub.The C-terminal five residues of Ub,RLRGG,are similar to the P5–P1 residues of the polyprotein substrates of the PL^(pro) and are responsible for the major part of the interaction between the two macromolecules.Through sitedirected mutagenesis,we demonstrate that conserved Asp165 and non-conserved Asp164 are important for the catalytic activities of MERS-CoV PL^(pro).The enzyme appears not to be optimized for catalytic efficiency; thus,replacement of Phe269 by Tyr leads to increased peptidolytic and deubiquitinating activities.Ubiquitin binding by MERS-CoV PL^(pro) involves remarkable differences compared to the corresponding complex with SARS-CoV PL^(pro).The structure and the mutational study help understand common and unique features of the deubiquitinating activity of MERS-CoV PL^(pro).