Structure of a three-dimensional domain-swapped dimer of the Helicobacter pylori type IV secretion system pilus protein CagL

Barden S, Schomburg B, Conradi J, Backert S, Sewald N, Niemann H. Structure of a three-dimensional domain-swapped dimer of the Helicobacter pylori type IV secretion system pilus protein CagL. Acta crystallographica. Section D, Biological crystallography. 2014;70(Pt 5):1391-1400.A new crystal form of the Helicobacter pylori type IV secretion system (T4SS) pilus protein CagL is described here. In contrast to two previously reported monomeric structures, CagL forms a three-dimensional domain-swapped dimer. CagL dimers can arise during refolding from inclusion bodies or can form spontaneously from purified monomeric CagL in the crystallization conditions. Monomeric CagL forms a three-helix bundle, with which the N-terminal helix is only loosely associated. In the new crystal form, the N-terminal helix is missing. The domain swap is owing to exchange of the C-terminal helix between the two protomers of a dimer. A loop-to-helix transition results in a long helix of 108 amino acids comprising the penultimate and the last helix of the monomer. The RGD motif of dimeric CagL adopts an α-helical conformation. In contrast to the previously reported structures, the conserved and functionally important C-terminal hexapeptide is resolved. It extends beyond the three-helix bundle as an exposed helical appendage. This new crystal form contributes to the molecular understanding of CagL by highlighting rigid and flexible regions in the protein and by providing the first view of the C-terminus. Based on the structural features, a previously unrecognized homology between CagL and CagI is discussed

Differences in Immunogenicity of Three Different Homo- and Heterologous Vaccination Regimens against SARS-CoV-2

Background: Due to findings on adverse reactions and clinical efficacy of different vaccinations against SARS-CoV-2, the administration of vaccination regimens containing both adenoviral vector vaccines and mRNA-based vaccines has become common. Data are still needed on the direct comparison of immunogenicity for these different regimens. Methods: We compared markers for immunogenicity (anti-S1 IgG/IgA, neutralizing antibodies, and T-cell response) with three different vaccination regimens (homologous ChAdOx1 nCoV-19 (n = 103), or mixture of ChAdOx1 nCoV-19 with mRNA-1273 (n = 116) or BNT162b2 (n = 105)) at two time points: the day of the second vaccination as a baseline and 14 days later. Results: All examined vaccination regimens elicited measurable immune responses that were significantly enhanced after the second dose. Homologous ChAdOx1 nCoV-19 was markedly inferior in immunogenicity to all other examined regimens after administration of the second dose. Between the heterologous regimens, mRNA-1273 as second dose induced greater antibody responses than BNT162b2, with no difference found for neutralizing antibodies and T-cell response. Discussion: While these findings allow no prediction about clinical protection, from an immunological point of view, vaccination against SARS-CoV-2 with an mRNA-based vaccine at one or both time points appears preferable to homologous vaccination with ChAdOx1 nCoV-19. Whether or not the demonstrated differences between the heterologous regimens are of clinical significance will be subject to further research

Antifreeze glycopeptide analogues: microwave-enhanced synthesis and functional studies

Heggemann C, Budke C, Schomburg B, et al. Antifreeze glycopeptide analogues: microwave-enhanced synthesis and functional studies. Amino Acids. 2010;38(1):213-222.Antifreeze glycoproteins enable life at temperatures below the freezing point of physiological solutions. They usually consist of the repetitive tripeptide unit (-Ala-Ala-Thr-) with the disaccharide alpha-D-galactosyl(1-3)-beta-N-acetyl-D-galactosamine attached to each hydroxyl group of threonine. Monoglycosylated analogues have been synthesized from the corresponding monoglycosylated threonine building block by microwave-assisted solid phase peptide synthesis. This method allows the preparation of analogues containing sequence variations which are not accessible by other synthetic methods. As antifreeze glycoproteins consist of numerous isoforms they are difficult to obtain in pure form from natural sources. The synthetic peptides have been structurally analyzed by CD and NMR spectroscopy in proton exchange experiments revealing a structure as flexible as reported for the native peptides. Microphysical recrystallization tests show an ice structuring influence and ice growth inhibition depending on the concentration, chain length and sequence of the peptides