Browsing by Author "Petrovskis, Ivars"

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    Comparative Immunogenicity in Rabbits of the Polypeptides Encoded by the 5′ Terminus of Hepatitis C Virus RNA
    (2015) Sominskaya, Irina; Jansons, Juris; Dovbenko, Anastasija; Petrakova, Natalia; Lieknina, Ilva; Mihailova, Marija; Latyshev, Oleg; Eliseeva, Olesja; Stahovska, Irina; Akopjana, Inara; Petrovskis, Ivars; Isaguliants, Maria; Rīga Stradiņš University
    Recent studies on the primate protection from HCV infection stressed the importance of immune response against structural viral proteins. Strong immune response against nucleocapsid (core) protein was difficult to achieve, requesting further experimentation in large animals. Here, we analyzed the immunogenicity of core aa 1-173, 1-152, and 147-191 and of its main alternative reading frame product F-protein in rabbits. Core aa 147-191 was synthesized; other polypeptides were obtained by expression in E. coli. Rabbits were immunized by polypeptide primes followed by multiple boosts and screened for specific anti-protein and anti-peptide antibodies. Antibody titers to core aa 147-191 reached 105; core aa 1-152, 5 × 105; core aa 1-173 and F-protein, 106. Strong immunogenicity of the last two proteins indicated that they may compete for the induction of immune response. The C-terminally truncated core was also weakly immunogenic on the T-cell level. To enhance core-specific cellular response, we immunized rabbits with the core aa 1-152 gene forbidding F-protein formation. Repeated DNA immunization induced a weak antibody and sustained proliferative response of broad specificity confirming a gain of cellular immunogenicity. Epitopes recognized in rabbits overlapped those in HCV infection. Our data promotes the use of rabbits for the immunogenicity tests of prototype HCV vaccines.
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    Crystal structure of the membrane attack complex assembly inhibitor BGA71 from the Lyme disease agent Borrelia bavariensis
    (2018-12-01) Brangulis, Kalvis; Akopjana, Inara; Petrovskis, Ivars; Kazaks, Andris; Kraiczy, Peter; Tars, Kaspars; Department of Human Physiology and Biochemistry
    Borrelia (B.) bavariensis, B. burgdorferi, B. afzelii, B. garinii, B. spielmanii, and B. mayonii are the causative agents in Lyme disease. Lyme disease spirochetes reside in infected Ixodes ticks and are transferred to mammalian hosts during tick feeding. Once transmitted, spirochetes must overcome the first line of defense of the innate immune system either by binding complement regulators or by terminating the formation of the membrane attack complex (MAC). In B. bavariensis, the proteins BGA66 and BGA71 inhibit complement activation by interacting with the late complement components C7, C8, and C9, as well as with the formed MAC. In this study, we have determined the crystal structure of the potent MAC inhibitor BGA71 at 2.9 Ǻ resolution. The structure revealed a cysteine cross-linked homodimer. Based on the crystal structure of BGA71 and the structure-based sequence alignment with CspA from B. burgdorferi, we have proposed a potential binding site for C7 and C9, both of which are constituents of the formed MAC. Our results shed light on the molecular mechanism of immune evasion developed by the human pathogenic Borrelia species to overcome innate immunity. These results will aid in the understanding of Lyme disease pathogenesis and pave the way for the development of new strategies to prevent Lyme disease.
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    Structural characterization of CspZ, a complement regulator factor H and FHL-1 binding protein from Borrelia burgdorferi
    (2014-06) Brangulis, Kalvis; Petrovskis, Ivars; Kazaks, Andris; Bogans, Janis; Otikovs, Martins; Jaudzems, Kristaps; Ranka, Renate; Tars, Kaspars; Rīga Stradiņš University
    Borrelia burgdorferi is the causative agent of Lyme disease and is found in two different types of hosts in nature - Ixodes ticks and various mammalian organisms. To initiate disease and survive in mammalian host organisms, B. burgdorferi must be able to transfer to a new host, proliferate, attach to different tissue and resist the immune response. To resist the host's immune response, B. burgdorferi produces at least five different outer surface proteins that can bind complement regulator factor H (CFH) and/or factor H-like protein 1 (CFHL-1). The crystal structures of two uniquely folded complement binding proteins, which belong to two distinct gene families and are not found in other bacteria, have been previously described. The crystal structure of the CFH and CFHL-1 binding protein CspZ (also known as BbCRASP-2 or BBH06) from B. burgdorferi, which belongs to a third gene family, is reported in this study. The structure reveals that the overall fold is different from the known structures of the other complement binding proteins in B. burgdorferi or other bacteria; this structure does not resemble the fold of any known protein deposited in the Protein Data Bank. The N-terminal part of the CspZ protein forms a four-helix bundle and has features similar to the FAT domain (focal adhesion targeting domain) and a related domain found in the vinculin/α-catenin family. By combining our findings from the crystal structure of CspZ with previous mutagenesis studies, we have identified a likely binding surface on CspZ for CFH and CFHL-1.