Factor I-mediated processing of complement fragments on HIV immune complexes targets HIV to CR2-expressing B cells and facilitates B cell-mediated transmission of opsonized HIV to T cells

Our study demonstrates that binding of complement-opsonized HIV to complement receptor type 1 on human erythrocytes (E) via C3b fragments is followed by a rapid normal human serum-mediated detachment of HIV from E. The release was dependent on the presence of factor I indicating a conversion of C3b fragments to iC3b and C3d on the viral surface. This in turn resulted in an efficient binding of opsonized HIV to CR2-expressing B cells, thus facilitating B cell-mediated transmission of HIV to T cells. These data provide a new dynamic view of complement opsonization of HIV, suggesting that association of virus with E might be a transient phenomenon and the factor I-mediated processing of C3b to iC3b and C3d on HIV targets the virus to complement receptor type 2-expressing cells. Thus, factor I in concert with CR1 on E and factor H in serum due to their cofactor activity are likely to be important contributors for the generation of C3d-opsonized infectious HIV reservoirs on follicular dendritic cells and/or B cells in HIV-infected individuals.     

Personal dosimetry of exposure to mobile telephone base stations? An epidemiologic feasibility study comparing the Maschek dosimeter prototype and the Antennessa DSP‐090 system

The aim of our study was to test the feasibility and reliability of personal dosimetry. Twenty-four hour exposure assessment was carried out in 42 children, 57 adolescents, and 64 adults using the Maschek dosimeter prototype. Self-reported exposure to mobile phone frequencies were compared with the dosimetry results. In addition, dosimetry readings of the Maschek device and those of the Antennessa DSP-090 were compared in 40 subjects. Self-reported exposures were not associated with dosimetry readings. The measurement results of the two dosimeters were in moderate agreement (r(Spearman) = 0.35; P = .03). Personal dosimetry for exposure to mobile phone base station might be feasible in epidemiologic studies. However, the consistency seems to be moderate.     

Synthesis and molecular structure of trinuclear mixed-metal cluster cations containing arene and hydrido ligands

The mixed-metal trinuclear cluster cations [H₃Ru₂(C₆Me₆)₂Os(C₆H₆)(O)]⁺ (1), [H₃Ru₂(1,2,4,5-C₆H₂Me₄)₂Os(p-MeC₆H₄ⁱPr)(O)]⁺ (2) and [H₃Ru₂(1,2,4,5-C₆H₂Me₄)₂Os(C₆H₆)(O)]⁺ (3) have been synthesised from the corresponding dinuclear precursors [H₃Ru₂(arene)₂]⁺ and the corresponding mononuclear complexes [Os(arene)(H₂O)₃]²⁺, isolated and characterised as the tetrafluoroborate and hexafluorophosphate salts. The cations 1, 2 and 3 are heteronuclear analogues of the cluster cation [H₃Ru₃(C₆H₆)(C₆Me₆)₂(O)]⁺ that possesses a homonuclear metallic core. The single-crystal X-ray structure analyses of [1][BF₄], [2][PF₆] and [3][PF₆] reveal an equiangular metal triangle despite the presence of an osmium atom in the metallic core.     

New mono and dinuclear arene ruthenium chloro complexes containing ester substituents

The dinuclear arene ruthenium complexes [RuCl₂{C₆H₅(CH₂)₃OCO-p-C₆H₄-OC₈H₁₇}]₂ (1) and [RuCl₂{p-C₆H₄(CH₂COOCH₂CH₃)₂}]₂ (2) have been obtained by dehydrogenation of the corresponding cyclohexadiene derivative with ruthenium chloride hydrate. The single-crystal X-ray structure analysis of 2 shows the arene ligands to be involved in slipped-parallel π-π stacking interactions with neighbouring molecules, thus forming infinite chains along the b-axis. The dinuclear complexes 1 and 2 react with two equivalents of triphenylphosphine (PPh₃) to give in excellent yield the corresponding mononuclear phosphine complexes [RuCl₂{C₆H₅(CH₂)₃OCO-p-C₆H₄-OC₈H₁₇}(PPh₃)] (3) and [RuCl₂{p-C₆H₄(CH₂COOCH₂CH₃)₂}(PPh₃)] (4), respectively. The single-crystal X-ray structure analysis of 4 reveals the formation of a dimer through two C-H?Cl interactions in the solid state.     

Structure and reaction geometry of geranylgeranyl diphosphate synthase from Sinapis alba

The crystal structure of the geranylgeranyl diphosphate synthase from Sinapis alba (mustard) has been solved in two crystal forms at 1.8 and 2.0 A resolutions. In one of these forms, the dimeric enzyme binds one molecule of the final product geranylgeranyl diphosphate in one subunit. The chainfold of the enzyme corresponds to that of other members of the farnesyl diphosphate synthase family. Whereas the binding modes of the two substrates dimethylallyl diphosphate and isopentenyl diphosphate at the allyl and isopentenyl sites, respectively, have been established with other members of the family, the complex structure presented reveals for the first time the binding mode of a reaction product at the isopentenyl site. The binding geometry of substrates and product in conjunction with the protein environment and the established chemistry of the reaction provide a clear picture of the reaction steps and atom displacements. Moreover, a comparison with a ligated homologous structure outlined an appreciable induced fit: helix alpha8 and its environment undergo a large conformational change when either the substrate dimethylallyl diphosphate or an analogue is bound to the allyl site; only a minor conformational change occurs when the other substrate isopentenyl diphosphate or the product is bound to the isopentenyl site.     

Influence of N-acylation of a peptide derived from human lactoferricin on membrane selectivity

Increasing numbers of bacterial strains being resistant to conventional antibiotics emphasize the urgent need for new antimicrobial agents. One strategy is based on host defence peptides that can be found in every organism including humans. We have studied the antimicrobial peptide LF11, derived from the pepsin cleavage product of human lactoferrin, known for its antimicrobial and lipid A-binding activity, and peptide C12LF11, the N-lauryl-derivative of LF11, which has owing to the attached hydrocarbon chain an additional hydrophobic segment. The influence of this hydrocarbon chain on membrane selectivity was studied using model membranes composed of dipalmitoylphosphatidylglycerol (DPPG), mimicking bacterial plasma membranes, and of dipalmitoylphosphatidylcholine (DPPC), a model system for mammalian membranes. A variety of biophysical techniques was applied. Thereby, we found that LF11 did not affect DPPC bilayers and showed only moderate effects on DPPG membranes in accordance with its non-hemolytic and weak antimicrobial activity. In contrast, the introduction of the N-lauryl group caused significant changes in the phase behaviour and lipid chain packing in both model membrane systems. These findings correlate with the in vitro tests on methicillin resistant S. aureus, E. coli, P. aeruginosa and human red blood cells, showing increased biological activity of C12LF11 towards these test organisms. This provides evidence that both electrostatic and hydrophobic interactions are crucial for biological activity of antimicrobial peptides, whereas a certain balance between the two components has to be kept, in order not to loose the specificity for bacterial membranes.     

Biochemical characterization of the class B acid phosphatase (AphA) of Escherichia coli MG1655

The AphA enzyme of Escherichia coli, a molecular class B periplasmic phosphatase that belongs to the DDDD superfamily of phosphohydrolases, was purified and subjected to biochemical characterization. Kinetic analysis with several substrates revealed that the enzyme essentially behaves as a broad-spectrum nucleotidase highly active on 3'- and 5'-mononucleotides and monodeoxynucleotides, but not active on cyclic nucleotides, or nucleotides di- and triphosphate. Mononucleotides are degraded to nucleosides, and AphA apparently does not exhibit any nucleotide phosphomutase activity. However, it can transphosphorylate nucleosides in the presence of phosphate donors. Kinetic properties of AphA are consistent with structural data, and suggest a role for the hydrophobic pocket present in the active site crevice, made by residues Phe 56, Leu71, Trp77 and Tyr193, in conferring preferential substrate specificity by accommodating compounds with aromatic rings. AphA was inhibited by several chelating agents, including EDTA, EGTA, 1,10-phenanthroline and dipicolinic acid, with EDTA being apparently the most powerful inhibitor.