Prion diseases are fatal transmissible neurodegenerative diseases affecting many mammalian species. The normal prion protein (PrP) converts into a pathological aggregated form, PrPSc, which is enriched in the â-sheet structure. While the high resolution structure of the normal PrP was determined, the structure of the converted form of PrP remains inaccessible tohigh resolution techniques. In order to map the PrP conversion process we introduced disulfide bridges into different positions within the globular domain of PrP, tethering selected secondary structure elements. The majority of tethered PrP mutants exhibited increased thermodynamic stability, nevertheless they converted efficiently. Only the disulfides which tether subdomain B1-H1-B2 to subdomain H2-H3 prevented PrP conversion in vitro and inprion infected cell cultures. Reduction of disulfides recovered the ability of these mutants to convert, demonstrating that the separation of subdomains is an essential step in conversion. Formation of disulfide-linked proteinase K-resistant dimers in fibrils composed of a pair of single cysteine mutants supports the model based on domain-swapped dimers as the building blocks of prion fibrils. In contrast to previously proposed structural models of PrPSc suggesting conversion of large secondary structure segments, we provide evidence for the conservation of secondary structure elements of the globular domain upon PrP conversion. Previous studies already showed that dimerization is the rate-limiting step in PrP conversion. We show that separation and swapping of subdomains of the globular domain is necessary for conversion. Therefore, we propose that domain-swapped dimer of PrP precedes amyloid formation and represents a potential target for therapeutic intervention.
COBISS.SI-ID: 4602394
Endosomal TLRs play an important role in innate immune response as well as in autoimmune processes. In the therapy of systemic lupus erythematosus, antimalarial drugs chloroquine, hydroxychloroquine, and quinacrine have been used for a long time. Their suppression of endosomal TLR activation has been attributed to the inhibition of endosomal acidification, which is a prerequisite for the activation of these receptors. We discovered that chloroquine inhibits only activation of endosomal TLRs by nucleic acids, whereas it augments activation of TLR8 by a small synthetic compound, R848. We detected direct binding of antimalarials to nucleic acids by spectroscopic experiments and determined their cellular colocalization. Further analysis revealed that other nucleic acid-binding compounds, such as propidium iodide, also inhibited activation of endosomal TLRs and colocalized with nucleic acidsto endosomes. We found that imidazoquinolines, which are TLR7/8 agonists,inhibit TLR9 and TLR3 even in the absence of TLR7 or TLR8, and their mechanism of inhibition is similar to the antimalarials. In contrast to bafilomycin, none of the tested antimalarials and imidazoquinolines inhibited endosomal proteolysis or increased the endosomal pH, confirming that inhibition of pH acidification is not the underlying cause of inhibition. We conclude that the direct binding of inhibitors to nucleic acids mask their TLR-binding epitope and may explain the efficiency of those compounds in the treatment of autoimmune diseases.
COBISS.SI-ID: 2971761
HIV-1 represents an elusive target for therapeutic compounds due to its high rate of mutation. Targeting structural patterns instead of a constantly changing specific 3D structure may represent an approach that is less sensitive to viral mutations. The V3 loop of gp120 of HIV-1, which is responsible for binding of viral gp120 to CCR5 or CXCR4 coreceptors, has already been identified as an effective target for the inhibition of viral entry. The peptide derived from the V3 loop of gp120 specifically interacts with the lipid A moiety of LPS, as does the full gp120 protein. NMR analysis of V3 in complex with LPS shows formation of an amphipathic turn. The interaction between LPS and V3 relies on the structural pattern, comprising a combination of hydrophobic and charge interactions, similar to the interaction between antimicrobial peptides and LPS. LPS inhibited binding of gp120 to the surface of target T cells. Nonendotoxic LPS antagonists inhibited viral infection, demonstrating the possibility for the development ofan inhibitor of HIV-1 attachment to T cells based on the recognition of a conserved structural pattern.
COBISS.SI-ID: 4677402