Crystallographic refinement and atomic models of a human Fc fragment and its complex with fragment B of protein A from Staphylococcus aureus at 2.9- and 2.8-.ANG. resolution

Solution conformation of the biantennary N-linked oligosaccharide of human serotransferrin using 1H NMR nuclear Overhauser effect measurements

The conformation in solution of the biantennary complex type oligosaccharide unit derived from human serotransferrin has been investigated using 1H-1H Nuclear Overhauser Effect (NOE) measurements at 300 MHz. From quantitation of the NOE, the alpha(1-3) antenna is shown to exist in a preferred solution conformation with respect to the mannosyl-chitobiose core. The flexibility of the alpha(1-6) arm, together with the absence of NOE data between this arm and the core, indicates that, in contrast to the alpha(1-3) arm the alpha(1-6) arm has no preferred conformation with respect to the core.

The effect of the chemical modification in human Fc gamma fragment on protein A and Fc receptor binding

The role of acidic side-chains on Fc gamma fragment in granulocyte receptor binding and in S. aureus protein A binding has been investigated by means of chemical modification. Alteration of a restricted number of carboxyl groups after 5 min of reaction is sufficient to abrogate the capacity of Fc to inhibit EA rosette formation by human neutrophils. More limited modification, which affects mainly the most exposed acidic chains, does not change receptor binding activity. In contrast, the interaction with protein A is largely unaffected, even under reaction conditions which are able to induce significant changes in the circular dichroism spectrum of Fc fragment. The results suggest that some acidic groups on Fc may be involved in the interaction with neutrophil receptor and that the binding to protein A and Fc receptor involves different sites.

Spin labeling of immunoglobulin M and E carbohydrates

The analysis of ESR spectra of spin-labeled human myeloma immunoglobulins M and E has shown the rotation of spin labels bound to carbohydrates to be restricted most probably due to close attachment of oligosaccharide chains to protein parts of molecules. The values of rotational correlation times for IgM, IgMs and Fc5, spin-labeled at carbohydrates, were found to be equal to 7,7 and 6 ns, respectively. These data pointed to the existence of internal lability of the Fc5 fragment. ESR spectra of IgE spin-labeled at carbohydrates also reflected restricted rotation of the spin label, but the presence of a more than one wide extremum spoke in favour of differences in the degree of immobilization between different oligosaccharide chains. The value of rotational correlation times calculated for IgE, spin-labeled at protein and carbohydrate moieties, were similar (60 and 66 ns). These data confirmed the previously found rigidity of IgE molecule as compared with IgG molecule.

Estimation of the secondary structure of protein A from S. aureus by CD-spectroscopy

The secondary structure of protein A(SpA) was estimated to 31% alpha-helix, 13% beta-structure and 56% random coil by CD-spectroscopy, which is close to the sum of the secondary structures of the SpA fragments. This supports that the SpA molecule is composed N-terminally of four Fc-binding units each consisting of two antiparallel alpha-helices interconnected by random coil segments and C-terminally of an region mainly in random coil.

Oxidative folding of cystine-rich peptides vs regioselective cysteine pairing strategies

The methodology of regioselective cysteine pairings in synthetic multiple-cystine peptides has progressed in the past years to an efficiency that allows for at least three specific inter- and intrachain disulfide bridgings. Conformational studies on various multiple-cystine peptides like hormones, protease inhibitors, and toxins revealed that these bioactive peptides, generated by posttranslational processing of precursor proteins, are folded into miniprotein-like compact globular structures of remarkable stability. This strongly suggests protein domain or subdomain properties of these families of peptides, and thus sufficient sequence-encoded information for correct oxidative refolding under appropriate experimental conditions. From intensive research on the mechanisms and pathways of oxidative refolding of proteins in vivo and in vitro, the efficient methods have emerged for simulating nature in the regeneration of native folds not only for intact proteins, but also for protein domains and subdomains. In fact, the results obtained in the oxidative folding of excised protein fragments and of relatively low mass products of posttranslational processings show that this procedure is indeed a simple way of preparing peptides with several disulfide bonds, if optimization of reaction conditions is performed in terms of redox buffer, temperature, and additives capable of disrupting aggregates and of stabilizing nascent secondary structures. Moreover, with increased knowledge about stable, small natural cystine frameworks, their use instead of artificial templates should facilitate engineering of synthetic miniproteins with specific conformation and tailored functions.