Michael G. Schwendinger

Detachment of Human Immunodeficiency Virus Type 1 from Germinal Centers by Blocking Complement Receptor Type 2

ABSTRACT After the transition from the acute to the chronic phase of human immunodeficiency virus (HIV) infection, complement mediates long-term storage of virions in germinal centers (GC) of lymphoid tissue. The contribution of particular complement receptors (CRs) to virus trapping in GC was studied on tonsillar specimens from HIV-infected individuals. CR2 (CD21) was identified as the main binding site for HIV in GC. Monoclonal antibodies (MAb) blocking the CR2-C3d interaction were shown to detach 62 to 77% of HIV type 1 from tonsillar cells of an individual in the presymptomatic stage. Although they did so at a lower efficiency, these antibodies were able to remove HIV from tonsillar cells of patients under highly active antiretroviral therapy, suggesting that the C3d-CR2 interaction remains a primary entrapment mechanism in treated patients as well. In contrast, removal of HIV was not observed with MAb blocking CR1 or CR3. Thus, targeting CR2 may facilitate new approaches toward a reduction of residual virus in GC.

Copper-catalyzed amino acid condensation in water — A simple possible way of prebiotic peptide formation

The recently reported condensation reaction of glycine to di- and triglycine in aqueous solution in the presence of higher concentrations of sodium chloride and copper ions has been investigated systematically and quantitatively using HPLC analytical methods. The influence of ‘environmental’ factors (temperature, concentration, atmosphere) are discussed. Numerous other metal ions have been investigated with respect to similar catalytic effects, and molybdenum results as the only one inducing peptide condensation, although to a much lesser extent. Experiments based on evaporation of water and redissolution lead to peptide condensation up to (gly)6 in concentrated solutions and produces peptides even starting from initially low concentrations.

Inhibition of HIV-1 infection in vitro by monoclonal antibodies to the complement receptor type 3 (CR3): An accessory role for CR3 during virus entry?

Adhesion molecules are known to contribute to infectivity of HIV-1. Here we tested whether the complement receptor type 3 (CR3, CD11b), an alpha(m)beta2 integrin, plays an accessory role in the infection process of HIV-1, because ICAM-1, a ligand of CR3, is present on the envelope of HIV-1. In addition, the viral transmembrane protein gp41 shares four regions of homology with the complement component C3, a further CR3 ligand. Infection of PBMCs with HIV-IIIB and primary isolates was partially inhibited by anti-CR3 antibodies. A peptide derived from the complement component C3, covering the CR3-binding site of C3 and sharing strong similarity to the immunosuppressive region of gp41, significantly reduced the HIV-1 titer in infection assays. Recombinant soluble gp41 (rsgp41) and the peptide covering the immunosuppressive domain of gp41 inhibited the rosetting of iC3b-coated sheep erythrocytes with U937 via complement receptors (CRs) with an efficiency comparable to monoclonal anti-CR antibodies. In addition, sub-populations of CD4 + and CD8 + T-cells isolated from HIV-infected individuals were found to upregulate CR3 as determined by FACS analysis and on the mRNA level. Since gp41 has been implicated in viral fusion, an interaction of its C3-homology region in gp41 or an interaction of ICAM on the surface of free virus with CRs might contribute to facilitate viral entry.

Salt induced peptide formation: on the selectivity of the copper induced peptide formation under possible prebiotic conditions

Abstract The reactivity of α, β and γ-amino acids in the copper(II)/NaCI-induced peptide formation reaction has been investigated. The stability constants and species distribution of amino acid/copper complexes were determined by the potentiometric method, and they indicate that copper complexes of the type Cu(aa)CI, being held responsible for the peptide formation, form preferentially with α-amino acids. The peptide formation itself has been investigated by experiments with constant volume and temperature and by evaporation cycle experiments with subsequent peptide analysis by means of HPLC. All possible dipeptide combinations of the investigated amino acids with glycine are observed, and α-amino acids are preferably linked to glycine when competing with their gb analogues. This preference of biologically relevant amino acids supplies another strong argument for the possible significance of the salt-induced peptide formation reaction for the chemical evolution of first peptides on the primordial earth.

Salt-induced formation of mixed peptides under possible prebiotic conditions

Abstract Investigations on the copper mediated peptide formation in aqueous solution in the presence of high amounts of NaCl have been extended to systems simultaneously containing glycine and alanine. Preferential formation of ala-gly compared to gly-ala is observed, total yields as high as 10.5% and 5.8% of initial glycine and alanine are found, and various tripeptides also form. Racemization occurs only to a limited extent.

On the possible role of montmorillonites in prebiotic peptide formation

SummaryThe ability of montmorillonite clay minerals for catalyzing peptide formation from amino acids in aqueous solution has been investigated using glycine and Cu2+ and Ca2+ containing montmorillonites as reaction systems. Evaporation cycle experiments showed that minor amounts of di- and tripeptide are formed from the amino acid. Further polymerization of dipeptide, however, seems to be more favoured by this reaction system than the initial step of dipeptide formation, and a possible role of clays in prebiotic peptide evolution could be seen therefore in the prolongation of peptide chains. Cu2+ ions in the clay matrix did not show any advantage over the usual Ca2+ ions embedded in natural montmorillonite.ZusammenfassungDie Fähigkeit von Tonmineralien der Montmorillonitklasse zur Katalyse von Peptidbildungsreaktionen aus Aminosäuren in wäßriger Lösung wurde am Beispiel von Glyzin und Kupfer sowie Kalzium und Morillonit untersucht. Experimente mit Verdampfungszyklen haben gezeigt, daß kleinere Mengen von Di- und Tripeptiden aus der Aminosäure gebildet werden. Die weitere Polymerisation von Dipeptiden hingegen scheint wesentlich leichter in diesem Reaktionssystem zu verlaufen als der Anfangsschritt der Bildung des Dipeptides. Eine mögliche Rolle von Tonmineralien in der präbiotischen Peptidevolution kann daher in der Verlängerung von Peptidketten gesehen werden. Kupferionen in der Tonmatrix zeigen keinerlei Vorteile gegenüber den üblichen Kalziumionen, die in natürlichem Montmorillonit vorkommen.

Investigations on the mechanism of the salt-induced peptide formation

The applicability of the salt-induced peptide formation in aqueous solution — the simplest model so far for peptide synthesis under primitive earth conditions — is demonstrated for valine as another amino acid, and the formation of mixed peptides in systems containing glycine, alanine and valine is investigated. The dominant dipeptides formed are Gly-Gly, Gly-Ala and Gly-Val, at longer reaction times sequence inversion produces Ala-Gly and, considerably slower, Val-Gly. Ala-Ala is also produced and the relative amounts of the diastereomers prove the high conservation of optical purity of the original amino acids over a considerable time. The results lead to some further conclusions about the reaction mechanism and the possible dominance of peptide sequences in primordial dipeptides.

Tracing uptake of C3DG-conjugated antigen into B-cells via complement receptor type 2

Electron microscopy was used to study the internalization and delivery of ligands for complement receptor type 2 (CR2, CD21) to endocytic compartments of B-lymphoblastoid Raji cells. Opsonized antigen was mimicked with purified C3dg conjugated to colloidal gold. C3dg-gold bound specifically to the cell surface in a time-dependent manner, and preincubation of the cells with a monoclonal antibody blocking the CR2 ligand-binding site completely inhibited any C3dg-gold binding. Notably, the binding of C3d-gold was confined to cell surface protrusions, eg, microvilli. C3dg-gold was apparently internalized through coated pits located at the bases of microvilli and could be traced to different compartments of the endocytic pathway. The morphologic characteristics and intracellular distribution of these multivesicular or multilaminar structures were compatible with those of compartments known to harbor major histocompatibility complex (MHC) class II molecules. Immunolabeling showed that the internalized C3dg-gold colocalized with MHC class II in these structures. These data provide the first ultrastructural evidence that complement-coated antigens are endocytosed by antigen-nonspecific B cells by CR2 and are delivered to the compartments in which peptide loading for antigen presentation occurs. They support the notion that CR2 may play a role in antigen presentation by B cells regardless of B-cell receptor specificity. (Blood. 2000;95:2617-2623)

Human Immunodeficiency Virus Type 1 gp41 Binds to Candida albicans via Complement C3-like Region

Oral candidiasis in human immunodeficiency virus type 1 (HIV-1)-infected persons is believed to be caused by the acquired T lymphocyte immunodeficiency. The direct interaction of C. albicans and HIV-1 in vitro was investigated. Twice as many yeasts adhered to cells transfected with the HIV-1 env gene as they did to controls. HIV-1 rsgp160 and rsgp41 but not rsgp120 were found to bind to Candida albicans via two C3-like regions within gp41. Normal human serum, but not C3-depleted serum, was able to inhibit rsgp41 binding to C. albicans. Vice versa, rsgp160 and rsgp41 were able to block rosetting of C. albicans with iC3b-coated sheep erythrocytes. Binding to C. albicans, and its inhibition by rsgp41 or rsgp160, was confirmed for the whole virus. Therefore, oral candidiasis in HIV-1-infected subjects may be augmented or may even be initiated by direct interaction between C. albicans and HIV-1 or HIV-1-infected cells.

A Monte Carlo simulation of a supersaturated sodium chloride solution

Abstract A simulation of a supersaturated sodium chloride solution with the Monte Carlo statistical thermodynamic method is reported. The water-water interactions are described by the Matsuoka-Clementi-Yoshimine (MCY) potential, while the ion-water potentials have been derived from ab initio calculations. Structural features of the solution have been evaluated, special interest being focused on possible precursors of nucleation.