Probing dynamics of HIV-1 nucleocapsid protein/target hexanucleotide complexes by 2-aminopurine

The nucleocapsid protein (NC) plays an important role in HIV-1, mainly through interactions with the genomic RNA and its DNA copies. Though the structures of several complexes of NC with oligonucleotides (ODNs) are known, detailed information on the ODN dynamics in the complexes is missing. To address this, we investigated the steady state and time-resolved fluorescence properties of 2-aminopurine (2Ap), a fluorescent adenine analog introduced at positions 2 and 5 of AACGCC and AATGCC sequences. In the absence of NC, 2Ap fluorescence was strongly quenched in the flexible ODNs, mainly through picosecond to nanosecond dynamic quenching by its neighboring bases. NC strongly restricted the ODN flexibility and 2Ap local mobility, impeding the collisions of 2Ap with its neighbors and thus, reducing its dynamic quenching. Phe16→Ala and Trp37→Leu mutations largely decreased the ability of NC to affect the local dynamics of 2Ap at positions 2 and 5, respectively, while a fingerless NC was totally ineffective. The restriction of 2Ap local mobility was thus associated with the NC hydrophobic platform at the top of the folded fingers. Since this platform supports the NC chaperone properties, the restriction of the local mobility of the bases is likely a mechanistic component of these properties

Characterisation of a synergohymenotropic toxin produced by Staphylococcus intermedius

AbstractStaphylococcal synergohymenotropic (SHT) toxins damage membranes of host defence cells and erythrocytes by the synergy of two secreted and non-associated proteins: class S and class F components. Whereas Panton-Valentine leucocidin (PVL), γ-hemolysin and Luk-M from Staphylococcus aureus are members of this toxin family, a new bi-component toxin (LukS-I + LukF-I) from Staphylococcus intermedius, a pathogen for small animals, was characterised and sequenced. It is encoded as a luk-I operon by two cotranscribed genes, like PVL. LukS-I + LukF-I shares a strong leukotoxicity of various PMNs, but only slight haemolytic properties on rabbit erythrocytes. When intradermally injected into rabbit skin, a 100 ng dose caused acute inflammatory reaction leading to tissue necrosis. The new SHT seemed to be largely distributed among various Staphylococcus intermedius strains

Treatment resistant Lyme arthritis caused by Borrelia garinii

Lyme arthritis is caused in Europe by three main pathogenic species of Borrelia burgdorferi sensu lato: Borrelia burgdorferi sensu stricto, Borrelia garinii, and Borrelia afzelii. Because few synovial samples have yet been analysed by species-specific DNA amplification methods, further studies are needed to define the spectra of clinical manifestations associated with these different species. Two cases of treatment resistant Lyme arthritis are reported here, in which DNA amplification of the flagellin gene followed by dot-blot hybridisation in the synovial fluid identified B garinii as the causative agent. Clinical and biological data did not differ from the usual descriptions of Lyme arthritis, but as the recently reported molecular mimicry between OspA and hLFA1 is not applicable to B garinii, the pathogenesis of the present cases remains unclear. Future studies should aim at assessing the role of B garinii in European Lyme arthritis and its possible pathogenic and therapeutic consequences.