A functionalized Sup35NM nanofibril-assisted oriented antibody capture in lateral flow immunoassay for sensitive detection of dengue type II NS1

Rapid and sensitive dengue non-structural protein 1 (NS1) detection assay is essential for the treatment of disease and currently releases high medical cost burdens. To address the limitations of conventional LFIA strips, we have developed an improved Sup35NM-Z-based LFIA that immobilizes antibodies on cellulose membranes in an orientated manner to increase the sensitivity of LFIA strips. A dual-functional Sup35NM nanofibril was fabricated by fusion with the antibody binding domain; resultant nanofibril from the amyloid Sup35NM was sprayed on the T-line to orientate the capture antibody and produces fluorescence signals. Antibody binding analysis showed that self-assembly of the Sup35NM monomer does not affect the binding activity of the Z-domain with the antibody. The NS1 for DENV-2 infection was chosen as a model target antigen to assess the feasibility of the Sup35NM-Z-domain-based LFIA platform. Under optimal conditions, the Sup35NM-Z-domain-based LFIA detected NS1 within 15 min with a detection limit of 1.29 ng/ml, while the detection limit of traditional LFIA with the same concentration of anti-NS1-Ab1 on the T-line by conventional physical adsorption was 2.20 ng/ml, 1.7 times higher than that of Sup35NM-Z-domain-based LFIA. As compared to traditional LFIAs, the Sup35NM-Z-based LFIA had a wide detection range of 1.29-625 ng/mL. The LFIA's clinical performance in identifying NS1 was also assessed using 15 clinical samples. The LFIA accurately recognized positive and negative samples, equal to 86.7% accuracy. The developed Sup35NM-Z-domain-based LFIA in this study offers great potential for the identification of target markers because of its greatly improved sensitivity and wider detection range.

Michler's hydrol blue elucidates structural differences in prion strains

Yeast prions provide self-templating protein-based mechanisms of inheritance whose conformational changes lead to the acquisition of diverse new phenotypes. The best studied of these is the prion domain (NM) of Sup35, which forms an amyloid that can adopt several distinct conformations (strains) that confer distinct phenotypes when introduced into cells that do not carry the prion. Classic dyes, such as thioflavin T and Congo red, exhibit large increases in fluorescence when bound to amyloids, but these dyes are not sensitive to local structural differences that distinguish amyloid strains. Here we describe the use of Michler's hydrol blue (MHB) to investigate fibrils formed by the weak and strong prion fibrils of Sup35NM and find that MHB differentiates between these two polymorphs. Quantum mechanical time-dependent density functional theory (TDDFT) calculations indicate that the fluorescence properties of amyloid-bound MHB can be correlated to the change of binding site polarity and that a tyrosine to phenylalanine substitution at a binding site could be detected. Through the use of site-specific mutants, we demonstrate that MHB is a site-specific environmentally sensitive probe that can provide structural details about amyloid fibrils and their polymorphs.

Kinetics and polymorphs of yeast prion Sup35NM amyloidogenesis

Amyloidogenic proteins often form many types of aggregates, which are a critical determinant of cytotoxicity and tissue specificity. However, the molecular mechanisms underlying the generation of distinct amyloids and their influence on cells remain largely unknown. We herein investigated the polymorphic amyloid formation of the yeast prion protein, Sup35NM, an intrinsically disordered N-terminal fragment of Sup35, under various conditions and its potential relationship to cytotoxicity. Sup35NM aggregated to amyloid fibrils with distinct kinetics, structures, morphologies, tinctorial properties, and conformational stabilities depending on the concentration of NaCl, pH, and temperature, indicating the polymorphic amyloidogenesis of Sup35NM. Detailed kinetic analyses of Sup35NM amyloid formation revealed a strong inverse correlation between the lag time and elongation rate without a correlation between kinetic and structural parameters. These results suggest that kinetic polymorphisms due to distinct nucleation and elongation rates result in structural polymorphs of amyloid fibrils, and also that conditions that enhance or inhibit the nucleation of Sup35NM promote or delay fibril growth. The deleterious effects of polymorphic Sup35NM amyloid fibrils on membrane integrity and cell vitality were minimal. We hypothesize that the innocuous polymorphic nature of Sup35NM amyloid fibrils may be beneficial for gaining time for prion infection prior to cell death.