IFI16 Preferentially Binds to DNA with Quadruplex Structure and Enhances DNA Quadruplex Formation.

Interferon-inducible protein 16 (IFI16) is a member of the HIN-200 protein family, containing two HIN domains and one PYRIN domain. IFI16 acts as a sensor of viral and bacterial DNA and is important for innate immune responses. IFI16 binds DNA and binding has been described to be DNA length-dependent, but a preference for supercoiled DNA has also been demonstrated. Here we report a specific preference of IFI16 for binding to quadruplex DNA compared to other DNA structures. IFI16 binds to quadruplex DNA with significantly higher affinity than to the same sequence in double stranded DNA. By circular dichroism (CD) spectroscopy we also demonstrated the ability of IFI16 to stabilize quadruplex structures with quadruplex-forming oligonucleotides derived from human telomere (HTEL) sequences and the MYC promotor. A novel H/D exchange mass spectrometry approach was developed to assess protein interactions with quadruplex DNA. Quadruplex DNA changed the IFI16 deuteration profile in parts of the PYRIN domain (aa 0-80) and in structurally identical parts of both HIN domains (aa 271-302 and aa 586-617) compared to single stranded or double stranded DNAs, supporting the preferential affinity of IFI16 for structured DNA. Our results reveal the importance of quadruplex DNA structure in IFI16 binding and improve our understanding of how IFI16 senses DNA. IFI16 selectivity for quadruplex structure provides a mechanistic framework for IFI16 in immunity and cellular processes including DNA damage responses and cell proliferation

Characterization of novel lectins from Burkholderia pseudomallei and Chromobacterium violaceum with seven-bladed β-propeller fold

Burkholderia pseudomallei and Chromobacterium violaceum are bacteria of tropical and subtropical soil and water that occasionally cause fatal infections in humans and animals. Microbial lectins mediate the adhesion of organisms to host cells, which is the first phase in the development of infection. Here we report the discovery of two novel lectins from the above-mentioned bacteria - BP39L and CV39L. The crystal structures revealed that the lectins possess a seven-bladed β-propeller fold. Functional studies conducted on a series of oligo- and polysaccharides confirmed the preference of BP39L for mannosylated saccharides and CV39L for rather more complex polysaccharides with a monosaccharide preference for β-L-fucose. The presented data indicate that the proteins belong to a currently unknown family of lectins

DNA sequences of oligonucleotides.

<p>DNA sequences of oligonucleotides.</p

Comparison of IFI16 DNA binding to structurally different DNA targets.

<p>EMSA was performed with 5 pmol of labeled oligonucleotides forming DS from human telomere sequence–DS HTEL (A) and G-quadruplex from one strand of the same sequence–Q HTEL (B), DS from NHE III region from <i>MYC</i> promoter–DS NHEIII (C) and G-quadruplex from one strand of the same sequence–Q NHEIII (D), SS (E) and cruciform (F) and increasing IFI16 concentrations (0 / 1.25 / 2.5 / 5 / 10 / 20 / 40 pmol), incubated in binding buffer (5 mM Tris-HCl, pH 7.0, 1 mM EDTA, 50 mM KCl and 0.01% Triton X-100) at 4°C for 15 min. Samples were electrophoresed on 4% non-denaturing polyacrylamide gel at 50V and 4°C for 3h. (G) Graphical representation of results obtained from densitometry analysis of free DNA bands from gels of IFI16 binding with SS A50, DS NHEIII, Q NHEIII and cruciform DNA targets from three independent experiments with SD. Schemes of DNA structures in A-F are not to scale.</p

Binding of IFI16 protein to supercoiled DNAs.

<p>(A) 100 ng sc pBluescript (lane 1–6) and sc pCMYC (lane 7–12) were incubated with increasing concentrations of IFI16 (molar ratio DNA:protein 1:0 / 1:1.25 / 1:2.5 / 1:5/ 1:10 / 1:20) in binding buffer (5 mM Tris-HCl, pH 7.0; 1 mM EDTA, 50 mM KCl and 0.01% Triton X-100) on ice for 15 min. The electrophoresis ran for 3 h at 100 V at 4°C. (B) 100 ng linear pBluescript (lane 1–6) and linear pCMYC (lane 7–12) were incubated with increasing concentrations of IFI16 (molar ratio DNA: protein 1:0 / 1:1.25 / 1:2.5 / 1:5/ 1:10 / 1:20) in binding buffer (5 mM Tris-HCl, pH 7.0; 1 mM EDTA, 50 mM KCl and 0.01% Triton X-100) on ice for 15 min. The electrophoresis ran for 3 h at 100 V at 4°C.</p

H/D exchange of IFI16 in response to DNA interaction.

<p>(A) H/D exchange of IFI16 in response to DNA interaction was analyzed in four reactions: IFI16 protein without DNA as a control, IFI16 with single stranded DNA oligonucleotide (SS DNA), IFI16 with double stranded DNA oligonucleotide (DS NHE III) and IFI16 with DNA forming quadruplex structure (Q NHEIII). H/D exchange was quenched at 900 s after addition of deuterium. The graph shows percentage deuteration of individual amino acids of IFI16 calculated as weighted average of corresponding peptides [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0157156#pone.0157156.ref053" target="_blank">53</a>]. Shaded area of the graph shows the areas not covered by peptides. The deuteration spectrum is aligned with the domain structure of IFI16 and with prediction of disordered regions (FoldIndex [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0157156#pone.0157156.ref054" target="_blank">54</a>]). (B) Structure of the first HIN-A domain (PDB 2OQ0) corresponding to amino acids 198–389 of IFI16 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0157156#pone.0157156.ref014" target="_blank">14</a>]. (C) Complex of the second HIN-B domain with DNA (PDB 3RNU) corresponding to amino acids 516–710 of IFI16 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0157156#pone.0157156.ref023" target="_blank">23</a>]. In (B) and (C) the helical linker peptide exhibiting the most significant changes in percentage of deuteration in the presence of quadruplex DNA is highlighted in red.</p

CD spectroscopy of quadruplexes and their stabilization by IFI16.

<p>(A) CD spectra of oligonucleotide HTEL in TE buffer after denaturation (blue line), in TE buffer + 50 mM NaCl (red line) and in TE buffer + 50 mM KCl (green line). (B) CD spectra of oligonucleotide NHEIII in TE buffer after denaturation (blue line), in TE buffer + 50 mM NaCl (red line) and in TE buffer + 50 mM KCl (green line). The schematic drawings represent quadruplex structures of HTEL and NHEIII sequences. (C) The effect of recombinant IFI16 on HTEL quadruplex formation in potassium ions. CD spectra description: HTEL oligonucleotide in TE buffer (blue line), HTEL in TE buffer with 50 mM KCl (red line), HTEL in TE buffer + protein buffer with final concentration 3.4 mM KCl (green line), HTEL in TE buffer + IFI16 in protein buffer at molar ratio 1:1 and final concentration 3.4 mM KCl (violet line), IFI16 protein in protein buffer with final concentration 3.4 mM KCl in TE buffer (black line). (D) The effect of recombinant IFI16 on NHEIII quadruplex formation in potassium ions. The same description of curves as in C (NHEIII instead of HTEL). (E) The effect of recombinant IFI16 on HTEL quadruplex formation in sodium ions. CD spectra description: HTEL oligonucleotide in TE buffer (blue line), HTEL in TE buffer with 50 mM NaCl (red line), HTEL in TE buffer + protein buffer with final concentration 3.2 mM NaCl (green line), HTEL in TE buffer + IFI16 in protein buffer at molar ratio 1:2 and final concentration 3.2 mM NaCl (violet line), IFI16 protein in protein buffer with final concentration 3.2 mM NaCl in TE buffer (black line). (F) The effect of recombinant IFI16 on NHEIII quadruplex formation in sodium ions. The same description of curves as in E (NHEIII instead of HTEL).</p

Enzyme-linked electrochemical detection of DNA fragments amplified by PCR in the presence of a biotinylated deoxynucleoside triphosphate using disposable pencil graphite electrodes

WOS: 000353219700015In this report, we present a simple electrochemical detection protocol for the detection of specific PCR-amplified DNA fragments, based on incorporation of biotin tags into DNA amplicons during PCR run in the presence of a biotinylated nucleoside triphosphate. For detection, an enzyme-linked electrochemical system involving streptavidin-alkaline phosphatase conjugate attached to the biotinylated DNA, adsorbed at the surface of a disposable pencil graphite electrode, is used. The enzyme converts an inactive indicator, 1-naphthyl phosphate, into electrochemically oxidizable indicator 1-naphthol that is subsequently detected. Excellent selectivity of this fast, facile, and inexpensive analysis not requiring any sophisticated electrode modification and its applicability for off-line monitoring of DNA amplification is demonstrated. Applications of the technique include detection of the presence of specific nucleotide sequences in biological samples, such as sequences related to pathogenic microorganism or transgenes. [GRAPHICS] .Czech Science FoundationGrant Agency of the Czech Republic [P206/11/1638, P206/11/P739]; ASCRCzech Academy of Sciences [RVO 68081707]; Turkish Scientific and Technological Research CouncilTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [111T050]; ASCR (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [111T050]This work was supported by the Czech Science Foundation (Grant P206/11/1638 to M. F. and P206/11/P739 to P. H.) and by the ASCR (RVO 68081707). A. E and M. F acknowledges to the grant of international joint project through between Turkish Scientific and Technological Research Council and the ASCR (TUBITAK Project No. 111T050)