We would like to thank our funding sources, including a generous gift from the Ware Foundation (to J.P.V.), The National Institutes of HealthGrant T32-CA079448 (to P.J.S.), and Ball State University startup funds (to P. J. S.). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

<ol>
	<li>Qin, Y., Hurley, L. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structures,+folding+patterns,+and+functions+of+intramolecular+DNA+G-quadruplexes+found+in+eukaryotic+promoter+regions.">Structures, folding patterns, and functions of intramolecular DNA G-quadruplexes found in eukaryotic promoter regions.</a> Biochimie. 90 (8), 1149-1171 (2008).</li><li>Stegle, O., Payet, L., Mergny, J. L., MacKay, D. J., Leon, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Predicting+and+understanding+the+stability+of+G-quadruplexes.">Predicting and understanding the stability of G-quadruplexes.</a> Bioinformatics. 25 (12), i374-i382 (2009).</li><li>Todd, A. K., Johnston, M., Neidle, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+prevalent+putative+quadruplex+sequence+motifs+in+human+DNA.">Highly prevalent putative quadruplex sequence motifs in human DNA.</a> Nucleic Acids Res. 33 (9), 2901-2907 (2005).</li><li>Huppert, J. L., Balasubramanian, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prevalence+of+quadruplexes+in+the+human+genome.">Prevalence of quadruplexes in the human genome.</a> Nucleic Acids Res. 33 (9), 2908-2916 (2005).</li><li>Bedrat, A., Lacroix, L., Mergny, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Re-evaluation+of+G-quadruplex+propensity+with+G4Hunter.">Re-evaluation of G-quadruplex propensity with G4Hunter.</a> Nucleic Acids Res. 44 (4), 1746-1759 (2016).</li><li>Mendoza, O., Bourdoncle, A., Boule, J. B., Brosh, R. M., Mergny, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=G-quadruplexes+and+helicases.">G-quadruplexes and helicases.</a> Nucleic Acids Res. 44 (5), 1989-2006 (2016).</li><li>Huppert, J. L., Balasubramanian, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=G-quadruplexes+in+promoters+throughout+the+human+genome.">G-quadruplexes in promoters throughout the human genome.</a> Nucleic Acids Res. 35 (2), 406-413 (2007).</li><li>Eddy, J., Maizels, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gene+function+correlates+with+potential+for+G4+DNA+formation+in+the+human+genome.">Gene function correlates with potential for G4 DNA formation in the human genome.</a> Nucleic Acids Res. 34 (14), 3887-3896 (2006).</li><li>Eddy, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=G4+motifs+correlate+with+promoter-proximal+transcriptional+pausing+in+human+genes.">G4 motifs correlate with promoter-proximal transcriptional pausing in human genes.</a> Nucleic Acids Res. 39 (12), 4975-4983 (2011).</li><li>Vaughn, J. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+DEXH+protein+product+of+the+DHX36+gene+is+the+major+source+of+tetramolecular+quadruplex+G4-DNA+resolving+activity+in+HeLa+cell+lysates.">The DEXH protein product of the DHX36 gene is the major source of tetramolecular quadruplex G4-DNA resolving activity in HeLa cell lysates.</a> J Biol Chem. 280 (46), 38117-38120 (2005).</li><li>Booy, E. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+RNA+helicase+RHAU+(DHX36)+unwinds+a+G4-quadruplex+in+human+telomerase+RNA+and+promotes+the+formation+of+the+P1+helix+template+boundary.">The RNA helicase RHAU (DHX36) unwinds a G4-quadruplex in human telomerase RNA and promotes the formation of the P1 helix template boundary.</a> Nucleic Acids Res. 40 (9), 4110-4124 (2012).</li><li>Creacy, S. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=G4+resolvase+1+binds+both+DNA+and+RNA+tetramolecular+quadruplex+with+high+affinity+and+is+the+major+source+of+tetramolecular+quadruplex+G4-DNA+and+G4-RNA+resolving+activity+in+HeLa+cell+lysates.">G4 resolvase 1 binds both DNA and RNA tetramolecular quadruplex with high affinity and is the major source of tetramolecular quadruplex G4-DNA and G4-RNA resolving activity in HeLa cell lysates.</a> J Biol Chem. 283 (50), 34626-34634 (2008).</li><li>Giri, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=G4+resolvase+1+tightly+binds+and+unwinds+unimolecular+G4-DNA.">G4 resolvase 1 tightly binds and unwinds unimolecular G4-DNA.</a> Nucleic Acids Res. 39 (16), 7161-7178 (2011).</li><li>Lattmann, S., Stadler, M. B., Vaughn, J. P., Akman, S. A., Nagamine, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+DEAH-box+RNA+helicase+RHAU+binds+an+intramolecular+RNA+G-quadruplex+in+TERC+and+associates+with+telomerase+holoenzyme.">The DEAH-box RNA helicase RHAU binds an intramolecular RNA G-quadruplex in TERC and associates with telomerase holoenzyme.</a> Nucleic Acids Res. 39 (21), 9390-9404 (2011).</li><li>Sexton, A. N., Collins, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+5'+guanosine+tracts+of+human+telomerase+RNA+are+recognized+by+the+G-quadruplex+binding+domain+of+the+RNA+helicase+DHX36+and+function+to+increase+RNA+accumulation.">The 5' guanosine tracts of human telomerase RNA are recognized by the G-quadruplex binding domain of the RNA helicase DHX36 and function to increase RNA accumulation.</a> Mol Cell Biol. 31 (4), 736-743 (2011).</li><li>Smaldino, P. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mutational+Dissection+of+Telomeric+DNA+Binding+Requirements+of+G4+Resolvase+1+Shows+that+G4-Structure+and+Certain+3'-Tail+Sequences+Are+Sufficient+for+Tight+and+Complete+Binding.">Mutational Dissection of Telomeric DNA Binding Requirements of G4 Resolvase 1 Shows that G4-Structure and Certain 3'-Tail Sequences Are Sufficient for Tight and Complete Binding.</a> PLoS One. 10 (7), e0132668 (2015).</li><li>Booy, E. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+RNA+helicase+RHAU+(DHX36)+suppresses+expression+of+the+transcription+factor+PITX1.">The RNA helicase RHAU (DHX36) suppresses expression of the transcription factor PITX1.</a> Nucleic Acids Res. 42 (5), 3346-3361 (2014).</li><li>Huang, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Yin+Yang+1+contains+G-quadruplex+structures+in+its+promoter+and+5'-UTR+and+its+expression+is+modulated+by+G4+resolvase+1.">Yin Yang 1 contains G-quadruplex structures in its promoter and 5'-UTR and its expression is modulated by G4 resolvase 1.</a> Nucleic Acids Res. 40 (3), 1033-1049 (2012).</li><li>Tran, H., Schilling, M., Wirbelauer, C., Hess, D., Nagamine, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Facilitation+of+mRNA+deadenylation+and+decay+by+the+exosome-bound,+DExH+protein+RHAU.">Facilitation of mRNA deadenylation and decay by the exosome-bound, DExH protein RHAU.</a> Mol Cell. 13 (1), 101-111 (2004).</li><li>Yoo, J. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=DHX36+enhances+RIG-I+signaling+by+facilitating+PKR-mediated+antiviral+stress+granule+formation.">DHX36 enhances RIG-I signaling by facilitating PKR-mediated antiviral stress granule formation.</a> PLoS Pathog. 10 (3), e1004012 (2014).</li><li>Lai, J. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+DEAH-box+helicase+RHAU+is+an+essential+gene+and+critical+for+mouse+hematopoiesis.">The DEAH-box helicase RHAU is an essential gene and critical for mouse hematopoiesis.</a> Blood. 119 (18), 4291-4300 (2012).</li><li>Zhang, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=DDX1,+DDX21,+and+DHX36+helicases+form+a+complex+with+the+adaptor+molecule+TRIF+to+sense+dsRNA+in+dendritic+cells.">DDX1, DDX21, and DHX36 helicases form a complex with the adaptor molecule TRIF to sense dsRNA in dendritic cells.</a> Immunity. 34 (6), 866-878 (2011).</li><li>Kim, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aspartate-glutamate-alanine-histidine+box+motif+(DEAH)/RNA+helicase+A+helicases+sense+microbial+DNA+in+human+plasmacytoid+dendritic+cells.">Aspartate-glutamate-alanine-histidine box motif (DEAH)/RNA helicase A helicases sense microbial DNA in human plasmacytoid dendritic cells.</a> Proc Natl Acad Sci U S A. 107 (34), 15181-15186 (2010).</li><li>Booy, E. P., McRae, E. K., McKenna, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biochemical+characterization+of+G4+quadruplex+telomerase+RNA+unwinding+by+the+RNA+helicase+RHAU.">Biochemical characterization of G4 quadruplex telomerase RNA unwinding by the RNA helicase RHAU.</a> Methods Mol Biol. 1259, 125-135 (2015).</li><li>Lattmann, S., Giri, B., Vaughn, J. P., Akman, S. A., Nagamine, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+the+amino+terminal+RHAU-specific+motif+in+the+recognition+and+resolution+of+guanine+quadruplex-RNA+by+the+DEAH-box+RNA+helicase+RHAU.">Role of the amino terminal RHAU-specific motif in the recognition and resolution of guanine quadruplex-RNA by the DEAH-box RNA helicase RHAU.</a> Nucleic Acids Res. 38 (18), 6219-6233 (2010).</li></ol>

The authors have nothing to disclose.

This protocol represents a highly efficient expression, purification, and quantification scheme for the isolation of the DHX36 gene product, G4-Resolvase1 (G4R1, also called RHAU and DHX36) (Figure 1). This protocol utilizes two purification steps: His-tag affinity purification on cobalt affinity beads and enzymatic purification on G4-DNA-conjugated beads. The latter step is unique in that it takes advantage of the tight affinity, high specificity, and catalytic unwinding activity that rG4R1 has for G4 s...

G4 structures are highly stable nucleic acid secondary structures that form within guanine-rich regions of DNA and RNA. G4 structures are stabilized via Hoogsteen-bonding interactions and coordinate bonding within the central cavity with monovalent cations (i.e.&#160;K+ and Na+) that significantly contribute to the remarkable thermal stability of G4 structures1,2. Early bioinformatics studies suggested that the human genome contains &#62;375,000 &#8220;potential G4-forming motifs&#8221;3,4. More recent study estimates suggest that the number of G4 motifs is higher by a factor of 2-55, while another study predicts 716,310 distinct potential G4-forming sequences in the human genome6. G4-forming sequences are evolutionarily conserved and not randomly dispersed in the genome. G4 motifs are enriched in gene coding regions, and upwards of 40% of all gene promoters contain G4 motifs7. Interestingly, the degree of enrichment of G4 motifs in a gene has been demonstrated to suggest the function of the gene. For example, proto-oncogenes and genes involved in development have significantly greater enrichment of G4 structures than tumor suppressor genes8,9.

With high thermal stabilities, a nearly ubiquitous presence throughout the genome, and the potential to significantly affect major cellular processes, it is unsurprising to find that the cell has evolved enzymes to manage these structures. One such enzyme is G4 Resolvase1 (G4R1; also called RHAU and DHX36), which we characterized as the source of the majority of tetramolecular G4-DNA resolving activity in human (HeLa) cells10. Since then, it has been shown that G4R1 tightly binds and catalytically unwinds tetramolecular and unimolecular G4-DNA and G4-RNA with the tightest reported KDs for a G4-binding protein11,12,13. Additionally, the G4-resolving activity of G4R1 has been implicated in a wide range of biochemical and cellular processes, including telomere/telomerase biology11,14,15,16, transcription and splicing17,18,19,20, development21, hematopoiesis21, and immune regulation22,23. With a preponderance of G4 sequences specifically situated throughout the genome and the diverse cellular processes that G4R1 has recently been implicated to be involved with, the ability to express and efficiently purify highly active rG4R1 will be of the utmost importance for elucidating the biochemical mechanisms and behaviors of this protein.

Here, we demonstrate a novel expression and purification scheme (Figure 1) that takes advantage of the ATP-dependent, G4-resolving activity of rG4R1 to efficiently isolate active enzyme. This scheme could be adapted to purify other ATP-dependent nucleic acid enzymes for which the product of the enzymatic reaction is no longer a substrate for binding, as is the case for G4R1.

<table><tbody><tr><td>TriEx4-DHX36 plasmid</td><td>Addgene</td><td>68368</td><td></td></tr><tr><td>Rosetta2(DE3)plysS competent cells</td><td>Novagen</td><td>71403-4</td><td></td></tr><tr><td>S.O.C medium</td><td>Thermo Fisher Scientific</td><td>15544034&amp;nbsp;</td><td></td></tr><tr><td>Difco Terrific Broth</td><td>Becton Dickinson</td><td>243820</td><td></td></tr><tr><td>Glycerol</td><td>Sigma-Aldrich</td><td>G5516</td><td></td></tr><tr><td>Chloramphenicol</td><td>Sigma-Aldrich</td><td>C1919</td><td>35 &amp;micro;g/mL in bacterial plates/large cultures</td></tr><tr><td>Carbenicillin (plant cell culture tested)</td><td>Sigma-Aldrich</td><td>C3416</td><td>50 &amp;micro;g/mL in bacterial plates/large cultures</td></tr><tr><td>Isopropyl &amp;beta;-D-1-thiogalactopyranoside (IPTG)</td><td>Sigma-Aldrich</td><td>I6758</td><td></td></tr><tr><td>Lysozyme (from chicken egg white)</td><td>Sigma-Aldrich</td><td>L6876</td><td></td></tr><tr><td>1 M Tris-HCl, pH 8</td><td>Universal Scientific Supply Co.&amp;nbsp;</td><td>1963-B</td><td>or from standard source</td></tr><tr><td>1 M Tris-HCl, pH 7</td><td>Universal Scientific Supply Co.&amp;nbsp;</td><td>1966</td><td>or from standard source</td></tr><tr><td>1.5 M Tris-HCl, pH 8.8</td><td></td><td></td><td>For casting resolving gel (for protein quantitation gel); From standard source</td></tr><tr><td>1 M Tris-HCl, pH 6.8</td><td></td><td></td><td>For casting stacking gel (for protein quantitation gel); From standard source</td></tr><tr><td>1 M Tris-Acetate, pH 7.8</td><td>Universal Scientific Supply Co.&amp;nbsp;</td><td>1981</td><td>or from standard source</td></tr><tr><td>70% Ethanol</td><td></td><td></td><td>From standard source</td></tr><tr><td>Magnesium chloride (1&amp;nbsp;M solution)</td><td>Life Technologies</td><td>AM9530G</td><td></td></tr><tr><td>Sodium chloride</td><td>Sigma-Aldrich</td><td>S7653</td><td></td></tr><tr><td>Sodium acetate</td><td>Sigma-Aldrich</td><td>S8750</td><td></td></tr><tr><td>20x SSC</td><td>Universal Scientific Supply Co.&amp;nbsp;</td><td>1665</td><td>or from standard source</td></tr><tr><td>&amp;beta;-mercaptoethanol (2-BME)</td><td>Sigma-Aldrich</td><td>63689</td><td></td></tr><tr><td>Protease inhibitor cocktail</td><td>Sigma-Aldrich</td><td>P8849</td><td></td></tr><tr><td>Leupeptin hemisulfate</td><td>Sigma-Aldrich</td><td>L8511</td><td></td></tr><tr><td>Streptavidin paramagnetic beads</td><td>Promega</td><td>Z5482</td><td></td></tr><tr><td>0.5 M EDTA, pH 8&amp;nbsp;</td><td>Universal Scientific Supply Co.&amp;nbsp;</td><td>0718</td><td>or from standard source</td></tr><tr><td>0.2 M EDTA, pH 6</td><td>Universal Scientific Supply Co.&amp;nbsp;</td><td></td><td>From standard source; initially adjust pH with NaOH, then adjust pH back down with HCl.&amp;nbsp;&amp;nbsp;</td></tr><tr><td>A-lactalbumin (Type 1 from bovine milk)</td><td>Sigma-Aldrich</td><td>L5385</td><td></td></tr><tr><td>Cobalt metal affinity beads</td><td>Clonetech</td><td>635502</td><td></td></tr><tr><td>L-Histidine</td><td>Sigma-Aldrich</td><td>H8000</td><td></td></tr><tr><td>Acetic acid, glacial</td><td>Fisher Scientific</td><td>A38-500</td><td></td></tr><tr><td>Adenosine 5&#039;-Triphosphate (from bacterial source)</td><td>Sigma</td><td>A7699</td><td></td></tr><tr><td>40% acrylamide/Bis solution (37.5:1)</td><td>Biorad</td><td>161-0148</td><td></td></tr><tr><td>Glycine</td><td>Sigma-Aldrich</td><td>50046</td><td>to make protein gel running buffer (192 mM glycine, 25 mM Tris Base, 0.1% SDS)</td></tr><tr><td>10% Sodium dodecyl sulfate (SDS)</td><td>Universal Scientific Supply Co.&amp;nbsp;</td><td>1667</td><td>to make protein gel running buffer (192 mM glycine, 25 mM Tris Base, 0.1% SDS); or from standard source</td></tr><tr><td>10x TBE&amp;nbsp;</td><td>Sigma-Aldrich</td><td>11666703001</td><td>or from standard source</td></tr><tr><td>Tris base</td><td>Fisher Scientific</td><td>BP152-1</td><td>to make protein gel running buffer (192 mM glycine, 25 mM Tris Base, 0.1% SDS); From standard source</td></tr><tr><td>TEMED</td><td>Sigma-Aldrich</td><td>411019</td><td></td></tr><tr><td>Ammonium persulfate (APS)</td><td>Sigma-Aldrich</td><td>A3678</td><td></td></tr><tr><td>Broad Range Protein MW markers</td><td>Promega</td><td>V8491</td><td></td></tr><tr><td>Biotinylated Z33 oligo (&quot;Z33-Bio&quot;)</td><td>Oligos Etc</td><td></td><td>5&amp;rsquo; AAA GTG ATG GTG GTG GGG GAA GGA TTC GGA CCT-biotin 3&amp;rsquo;</td></tr><tr><td>TAMRA-Z33 oligo (&quot;Z33-TAM&quot;)</td><td>Oligos Etc</td><td></td><td>5&amp;rsquo; TAMRA-AAA GTG ATG GTG GTG GGG GAA GGA TTC GGA CCT 3&amp;rsquo;</td></tr><tr><td>Fluor-coated TLC plate</td><td>Life Technologies</td><td>AM10110</td><td></td></tr><tr><td>Ficoll</td><td>Sigma-Aldrich</td><td>F2637</td><td>30% in H&lt;sub&gt;2&lt;/sub&gt;O</td></tr><tr><td>Coomassie R-250</td><td>Sigma-Aldrich</td><td>27816</td><td></td></tr><tr><td>Methanol</td><td>Fisher Scientific</td><td>A412</td><td></td></tr><tr><td>Multiband UV lamp</td><td></td><td></td><td>Capable of emitting UV light at 365 nm</td></tr><tr><td>Table-top centrifuge (with swinging bucket rotor)</td><td></td><td></td><td>Capable of being cooled to 4 &amp;deg;C</td></tr><tr><td>Microcentrifuge</td><td></td><td></td><td>Capable of being cooled to 4 &amp;deg;C</td></tr><tr><td>Digital Sonfier</td><td>Branson</td><td></td><td>Or equivalent capable of delivering sonication pulses (30% amplitude, 2 s ON/2 s OFF)</td></tr><tr><td>50 &amp;deg;C water bath</td><td></td><td></td><td>For formation of Z33 into quadruplex</td></tr><tr><td>37 &amp;deg;C incubator for bacteria</td><td></td><td></td><td>For bacterial transformations and initial overnight growth of large cultures of Rosetta2 &lt;em&gt;E. coli&lt;/em&gt; transformed with TriEx4-DHX36</td></tr><tr><td>37 &amp;deg;C/14&amp;nbsp;&amp;deg;C shaking incubator for bacteria</td><td></td><td></td><td>For growth and protein induction of large cultures of Rosetta2 &lt;em&gt;E. coli&lt;/em&gt; transformed with TriEx4-DHX36</td></tr><tr><td>Spectrophotometer</td><td></td><td></td><td>capable of reading OD600; capable of reading oligomer concentrations based on base sequence (such as Biorad SmartSpec 3000)</td></tr><tr><td>Thermometer</td><td></td><td></td><td>From standard source</td></tr><tr><td>PCR strip tubes</td><td></td><td></td><td>From standard source</td></tr><tr><td>15 and 50 mL centrifuge tubes (polypropylene)</td><td></td><td></td><td>From standard source</td></tr><tr><td>Microcentrifuge tubes (2.0 mL)</td><td></td><td></td><td>From standard source</td></tr><tr><td>500 mL centrifuge bottles (polypropylene)</td><td>Thermo Scientific</td><td>3141-0500</td><td></td></tr><tr><td>Standard array of pipet tips and serological pipettes</td><td></td><td></td><td>From standard source</td></tr><tr><td>Gel-loading tips</td><td></td><td></td><td>From standard source</td></tr><tr><td>Automatic repeating pipette</td><td></td><td></td><td>For quick aliquoting of rG4R1; From standard source</td></tr><tr><td>Thermal cycler</td><td></td><td></td><td>From standard source</td></tr><tr><td>Liquid Nitrogen</td><td></td><td></td><td>From standard source</td></tr><tr><td>Dry ice</td><td></td><td></td><td>From standard source</td></tr><tr><td>Laemlli sample buffer&amp;nbsp;</td><td>Biorad</td><td>161-0737</td><td></td></tr><tr><td>Apparatus for running large slab gels</td><td>Biorad</td><td></td><td>We have used the Protean II xi cell apparatus from Biorad</td></tr><tr><td>Magnet</td><td>Life Technologies</td><td>12301D</td><td>We use a magnet from One Lambda (Now a Thermo Fisher Scientific brand); and Life is also a subsidiary of Thermo, and thus the magnet listed here should be a suitable replacement</td></tr><tr><td>Razor blades</td><td></td><td></td><td>From standard source</td></tr><tr><td>Filter paper and funnel</td><td></td><td></td><td>From standard source</td></tr><tr><td>Glass casserole dish</td><td></td><td></td><td>From standard source</td></tr><tr><td>Orbital shaker</td><td></td><td></td><td>From standard source</td></tr><tr><td>Kimwipes</td><td></td><td></td><td>From standard source</td></tr><tr><td>Clear sheet protectors</td><td></td><td></td><td>From standard source</td></tr><tr><td>Scanner and associated TWAIN software</td><td></td><td></td><td>From standard source</td></tr><tr><td>Image analysis software</td><td></td><td></td><td>Such as Fuji Multiguage, or equivalent</td></tr><tr><td>Microsoft Excel</td><td></td><td></td><td>Or equivalent&amp;nbsp;</td></tr></tbody></table>

a g-quadruplex dna-affinity approach for purification of enzymatically active g4 resolvase1

Higher-order nucleic acid structures called G-quadruplexes (G4s, G4 structures) can form in guanine-rich regions of both DNA and RNA and are highly thermally stable. There are &#62;375,000 putative G4-forming sequences in the human genome, and they are enriched in promoter regions, untranslated regions (UTRs), and within the telomeric repeat. Due to the potential for these structures to affect cellular processes, such as replication and transcription, the cell has evolved enzymes to manage them. One such enzyme is G4 Resolvase 1 (G4R1), which was biochemically co-characterized by our laboratory and Nagamine et al. and found to bind extremely tightly to both G4-DNA and G4-RNA (Kd in the low-pM range). G4R1 is the source of the majority of G4-resolving activity in HeLa cell lysates and has since been implicated to play a role in telomere metabolism, lymph development, gene transcription, hematopoiesis, and immune surveillance. The ability to efficiently express and purify catalytically active G4R1 is of importance for laboratories interested in gaining further insight into the kinetic interaction of G4 structures and G4-resolving enzymes. Here, we describe a detailed method for the purification of recombinant G4R1 (rG4R1). The described procedure incorporates the traditional affinity-based purification of a C-terminal histidine-tagged enzyme expressed in human codon-optimized bacteria with the utilization of the ability of rG4R1 to bind and unwind G4-DNA to purify highly active enzyme in an ATP-dependent elution step. The protocol also includes a quality-control step where the enzymatic activity of rG4R1 is measured by examining the ability of the purified enzyme to unwind G4-DNA. A method is also described that allows for the quantification of purified rG4R1. Alternative adaptations of this protocol are discussed.

This protocol (Figure 1) routinely yields nearly pure, catalytically active rG4R1. As a measure of enzymatic activity, it is typically observed that 50% of 0.2 pmol of TAMRA-labeled tetramolecular G4-DNA is converted into monomers within the 0.2 - 0.013 &#181;L range of rG4R1, as assayed by the G4 activity assay outlined above (Figure 2). Coomassie staining of purified rG4R1 indicates a single band at the expected 120 kDa size, with a minor contaminating band at ~75 kDa, which may repres...

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A G-quadruplex DNA-affinity Approach for Purification of Enzymatically Active G4 Resolvase1

G4 Resolvase1 binds to G-quadruplex (G4) structures with the tightest reported affinity for a G4-binding protein and represents the majority of the G4-DNA unwinding activity in HeLa cells. We describe a novel protocol that harnesses the affinity and ATP-dependent unwinding activity of G4-Resolvase1 to specifically purify catalytically active recombinant G4R1.

Higher-order nucleic acid structures called G-quadruplexes (G4s, G4 structures) can form in guanine-rich regions of both DNA and RNA and are highly ...

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Research

JoVE Journal

Biochemistry

9.6K Views.  Wake Forest School of Medicine.  G4 Resolvase1 bindt aan G-quadruplex (G4) met de kleinste structuren gerapporteerde affiniteit voor een G4-bindend eiwit en vertegenwoordigt het merendeel van de G4-DNA afwikkelen activiteit in HeLa-cellen. We beschrijven een nieuw protocol dat de affiniteit en ATP-afhankelijke afwikkelen activiteit van de G4-Resolvase1 gordels om specifiek te zuiveren katalytisch actieve recombinant G4R1. 

Video: A G-quadruplex DNA-affinity Approach for Purification of Enzymatically Active G4 Resolvase1

Directed Protein Packaging within Outer Membrane Vesicles from Escherichia coli: Design, Production and Purification

An increasing interest in applying synthetic biology techniques to program outer membrane vesicles (OMV) are leading to some very interesting and unique applications for OMV where traditional nanoparticles are proving too difficult to synthesize. To date, all Gram-negative bacteria have been shown to produce OMV demonstrating packaging of a variety of cargo that includes small molecules, peptides, proteins and genetic material. Based on their diverse cargo, OMV are implicated in many biological processes ranging from cell-cell communication to gene transfer and delivery of virulence factors depending upon which bacteria are producing the OMV. Only recently have bacterial OMV become accessible for use across a wide range of applications through the development of techniques to control and direct packaging of recombinant proteins into OMV. This protocol describes a method for the production, purification, and use of enzyme packaged OMV providing for improved overall production of recombinant enzyme, increased vesiculation, and enhanced enzyme stability. Successful utilization of this protocol will result in the creation of a bacterial strain that simultaneously produces a recombinant protein and directs it for OMV encapsulation through creating a synthetic linkage between the recombinant protein and an outer membrane anchor protein. This protocol also details methods for isolating OMV from bacterial cultures as well as proper handling techniques and things to consider when adapting this protocol for use for other unique applications such as: pharmaceutical drug delivery, medical diagnostics, and environmental remediation.

Directed Protein Packaging within Outer Membrane Vesicles from Escherichia coli: Design, Production and Purification

A protocol for the production, purification, and use of enzyme packaged outer membrane vesicles (OMV) providing for enhanced enzyme stability for implementation across diverse applications is presented.

An increasing interest in applying synthetic biology techniques to program outer membrane vesicles (OMV) are leading to some very interesting and unique ...

Kinetics of Lagging-strand DNA Synthesis In Vitro by the Bacteriophage T7 Replication Proteins

Here we provide protocols for the kinetic examination of lagging-strand DNA synthesis in vitro by the replication proteins of bacteriophage T7. The T7 replisome is one of the simplest replication systems known, composed of only four proteins, which is an attractive feature for biochemical experiments. Special emphasis is placed on the synthesis of ribonucleotide primers by the T7 primase-helicase, which are used by DNA polymerase to initiate DNA synthesis. Because the mechanisms of DNA replication are conserved across evolution, these protocols should be applicable, or useful as a conceptual springboard, to investigators using other model systems. The protocols described here are highly sensitive and an experienced investigator can perform these experiments and obtain data for analysis in about a day. The only specialized piece of equipment required is a rapid-quench flow instrument, but this piece of equipment is relatively common and available from various commercial sources. The major drawbacks of these assays, however, include the use of radioactivity and the relative low throughput.

Kinetics of Lagging-strand DNA Synthesis In Vitro by the Bacteriophage T7 Replication Proteins

We describe sensitive, gel-based discontinuous assays to examine the kinetics of lagging-strand initiation using the replication proteins of bacteriophage T7.

Here we provide protocols for the kinetic examination of lagging-strand DNA synthesis in vitro by the replication proteins of bacteriophage T7. The T7 ...

Genetics

Expression, Purification, and Antimicrobial Activity of S100A12

Calgranulin proteins are important mediators of innate immunity and are members of the S100 class of the EF-hand family of calcium binding proteins. Some S100 proteins have the capacity to bind transition metals with high affinity and effectively sequester them away from invading microbial pathogens in a process that is termed "nutritional immunity". S100A12 (EN-RAGE) binds both zinc and copper and is highly abundant in innate immune cells such as macrophages and neutrophils. We report a refined method for the expression, enrichment and purification of S100A12 in its active, metal-binding configuration. Utilization of this protein in bacterial growth and viability analyses reveals that S100A12 has antimicrobial activity against the bacterial pathogen, Helicobacter pylori. The antimicrobial activity is predicated on the zinc-binding activity of S100A12, which chelates nutrient zinc, thereby starving H. pylori which requires zinc for growth and proliferation.

Here, we present a method to express and purify S100A12 (calgranulin C). We describe a protocol to measure its antimicrobial activity against the human pathogen H. pylori.

Calgranulin proteins are important mediators of innate immunity and are members of the S100 class of the EF-hand family of calcium binding proteins. Some ...

A Tandem Liquid Chromatography&#8211;Mass Spectrometry-based Approach for Metabolite Analysis of Staphylococcus aureus

In an effort to thwart bacterial pathogens, hosts often limit the availability of nutrients at the site of infection. This limitation can alter the abundances of key metabolites to which regulatory factors respond, adjusting cellular metabolism. In recent years, a number of proteins and RNA have emerged as important regulators of virulence gene expression. For example, the CodY protein responds to levels of branched-chain amino acids and GTP and is widely conserved in low G+C Gram-positive bacteria. As a global regulator in Staphylococcus aureus, CodY controls the expression of dozens of virulence and metabolic genes. We hypothesize that S. aureus uses CodY, in part, to alter its metabolic state in an effort to adapt to nutrient-limiting conditions potentially encountered in the host environment. This manuscript describes a method for extracting and analyzing metabolites from S. aureus using liquid chromatography coupled with mass spectrometry, a protocol that was developed to test this hypothesis. The method also highlights best practices that will ensure rigor and reproducibility, such as maintaining biological steady state and constant aeration without the use of continuous chemostat cultures. Relative to the USA200 methicillin-susceptible S. aureus isolate UAMS-1 parental strain, the isogenic codY mutant exhibited significant increases in amino acids derived from aspartate (e.g., threonine and isoleucine) and decreases in their precursors (e.g., aspartate and O-acetylhomoserine). These findings correlate well with transcriptional data obtained with RNA-seq analysis: genes in these pathways were up-regulated between 10- and 800-fold in the codY null mutant. Coupling global analyses of the transcriptome and the metabolome can reveal how bacteria alter their metabolism when faced with environmental or nutritional stress, providing potential insight into the physiological changes associated with nutrient depletion experienced during infection. Such discoveries may pave the way for the development of novel anti-infectives and therapeutics.

Here we describe a protocol for the extraction of metabolites from Staphylococcus aureus and their subsequent analysis via liquid chromatography and mass spectrometry.

In an effort to thwart bacterial pathogens, hosts often limit the availability of nutrients at the site of infection. This limitation can alter the ...

Single-molecule Manipulation of G-quadruplexes by Magnetic Tweezers

Non-canonical nucleic acid secondary structure G-quadruplexes (G4) are involved in diverse cellular processes, such as DNA replication, transcription, RNA processing, and telomere elongation. During these processes, various proteins bind and resolve G4 structures to perform their function. As the function of G4 often depends on the stability of its folded structure, it is important to investigate how G4 binding proteins regulate the stability of G4. This work presents a method to manipulate single G4 molecules using magnetic tweezers, which enables studies of the regulation of G4 binding proteins on a single G4 molecule in real time. In general, this method is suitable for a wide scope of applications in studies for proteins/ligands interactions and regulations on various DNA or RNA secondary structures.

A single-molecule magnetic tweezers platform to manipulate G-quadruplexes is reported, which allows for the study of G4 stability and regulation by various proteins.

Non-canonical nucleic acid secondary structure G-quadruplexes (G4) are involved in diverse cellular processes, such as DNA replication, transcription, RNA ...

Identifying G-Quadruplexes in a DNA Template Using Chemical Mapping

In Vitro Chemical Mapping of G-Quadruplex DNA Structures by Bis-3-Chloropiperidines

G-quadruplexes (G4s) are biologically relevant, non-canonical DNA structures that play an important role in gene expression and diseases, representing significant therapeutic targets. Accessible methods are required for the in vitro characterization of DNA within potential G-quadruplex-forming sequences (PQSs). B-CePs are a class of alkylating agents that have proven to be useful chemical probes for investigation of the higher-order structure of nucleic acids. This paper describes a new chemical mapping assay exploiting the specific reactivity of B-CePs with the N7 of guanines, followed by direct strand cleavage at the alkylated Gs. 
Namely, to distinguish G4 folds from unfolded DNA forms, we use B-CeP 1 to probe the thrombin-binding aptamer (TBA), a 15-mer DNA able to assume the G4 arrangement. Reaction of B-CeP-responding guanines with B-CeP 1 yields products that can be resolved by high-resolution polyacrylamide gel electrophoresis (PAGE) at a single-nucleotide level by locating individual alkylation adducts and DNA strand cleavage at the alkylated guanines. Mapping using B-CePs is a simple and powerful tool for the in vitro characterization of G-quadruplex-forming DNA sequences, enabling the precise location of guanines involved in the formation of G-tetrads.

Author Spotlight: Characterizing DNA G-Quadruplex by Bis-3-Chloropiperidine Based Chemical Mapping 

Bis-3-chloropiperidines (B-CePs) are useful chemical probes to identify and characterize G-quadruplex structures in DNA templates in vitro. This protocol details the procedure to perform probing reactions with B-CePs and to resolve reaction products by high-resolution polyacrylamide gel electrophoresis.

G-quadruplexes (G4s) are biologically relevant, non-canonical DNA structures that play an important role in gene expression and diseases, representing ...

CMG-Mediated DNA Unwinding Observed by ssDNA-RPA Tract Growth

Single-Molecule Real-Time Visualization of DNA Unwinding by CMG Helicase

Faithful genome duplication is essential for preserving the genetic stability of dividing cells. DNA replication is carried out during the S phase by a dynamic complex of proteins termed the replisome. At the heart of the replisome is the&#160;CDC45-MCM2-7-GINS (CMG) helicase, which separates the two strands of the DNA double helix such that DNA polymerases can copy each strand. During genome duplication, replisomes must overcome a plethora of obstacles and challenges. Each of these threatens genome stability, as failure to replicate DNA completely and accurately can lead to mutations, diseases, or cell death. Therefore, it is of great interest to understand how CMG functions in the replisome during both normal replication and replication stress. Here, we describe a total internal reflection fluorescence (TIRF) microscopy assay using recombinant purified proteins, which allows for real-time visualization of surface-tethered stretched DNA molecules by individual CMG complexes. This assay provides a powerful platform to investigate CMG behavior at the single-molecule level, allowing helicase dynamics to be directly observed with real-time control over reaction conditions.

Author Spotlight: Unraveling the Dynamics of Eukaryotic DNA Replication Through Single-Molecule Visualization

This protocol demonstrates performing a single-molecule assay for live visualization of DNA unwinding by CMG helicase. It describes (1) preparing a DNA substrate, (2) purifying fluorescently labeled Drosophila melanogaster CMG helicase, (3) preparing a microfluidic flow cell for total internal reflection fluorescence (TIRF) microscopy, and (4) the single-molecule DNA unwinding assay.

Faithful genome duplication is essential for preserving the genetic stability of dividing cells. DNA replication is carried out during the S phase by a ...

Iterative Optimization of DNA Duplexes for Crystallization of SeqA-DNA Complexes

Escherichia coli SeqA is a negative regulator of DNA replication that prevents premature reinitiation events by sequestering hemimethylated GATC clusters within the origin of replication1. Beyond the origin, SeqA is found at the replication forks, where it organizes newly replicated DNA into higher ordered structures2. SeqA associates only weakly with single GATC sequences, but it forms high affinity complexes with DNA duplexes containing multiple GATC sites. The minimal functional and structural unit of SeqA is a dimer, thereby explaining the requirement of at least two GATC sequences to form a high-affinity complex with hemimethylated DNA3. Additionally, the SeqA architecture, with the oligomerization and DNA-binding domains separated by a flexible linker, allows binding to GATC repeats separated by up to three helical turns. Therefore, understanding the function of SeqA at a molecular level requires the structural analysis of SeqA bound to multiple GATC sequences. In protein-DNA crystallization, DNA can have none to an exceptional effect on the packing interactions depending on the relative sizes and architecture of the protein and the DNA. If the protein is larger than the DNA or footprints most of the DNA, the crystal packing is primarily mediated by protein-protein interactions. Conversely, when the protein is the same size or smaller than the DNA or it only covers a fraction of the DNA, DNA-DNA and DNA-protein interactions dominate crystal packing. Therefore, crystallization of protein-DNA complexes requires the systematic screening of DNA length4 and DNA ends (blunt or overhang)5-7. In this report, we describe how to design, optimize, purify and crystallize hemimethylated DNA duplexes containing tandem GATC repeats in complex with a dimeric variant of SeqA (SeqA&Delta;(41-59)-A25R) to obtain crystals suitable for structure determination.

Crystal structure of protein&#x2013;DNA complexes can provide insight into protein function, mechanism, as well as, the nature of the specific interaction. Here, we report how to optimize the length, sequence and ends of duplex DNA for co-crystallization with Escherichia coli SeqA, a negative regulator of replication initiation.

Escherichia coli SeqA is a negative regulator of DNA replication that prevents premature reinitiation events by sequestering hemimethylated GATC clusters ...

Biology

Aptamer-Based Target Detection Facilitated by a 3-Stage G-Quadruplex Isothermal Exponential Amplification Reaction

Aptamers are target-recognition molecules that bind with high affinity and specificity. These characteristics can be leveraged to control other molecules with signal-generation capability. For the system described herein, target recognition through an aptameric domain, Stem II of a modified hammerhead ribozyme, activates the self-cleaving ribozyme by stabilizing the initially unstructured construct. The cis-cleaving RNA acts at the junction of Stem III and Stem I, creating two cleavage products. The longer cleavage product primes an isothermal exponential amplification reaction (EXPAR) of the two similar catalytically active G-quadruplexes. Those resulting amplification products catalyze peroxidase reduction, which is coupled to the reduction of a colorimetric substrate with an output that the naked eye can detect. The 3-part system described in the present study improves detection modalities such as enzyme-linked immunosorbent assays (ELISAs) by producing a visually detectable signal for indicating the presence of as low as 0.5 &#181;M theophylline in as little as 15 min.

The present protocol demonstrates the use of a fast, 3-stage, aptamer-based exponential amplification assay to detect targets. Sample preparation, signal amplification, and color development are covered to implement this system to recognize the presence of theophylline over that of caffeine.

Aptamers are target-recognition molecules that bind with high affinity and specificity. These characteristics can be leveraged to control other molecules ...

Bioengineering

Single-Molecule Fluorescence Visualization of DNA Polymerase Dynamics at G-Quadruplexes

The ability of proteins&#160;involved in eukaryotic DNA replication to&#160;overcome obstacles &#8212; such as protein and DNA &#39;roadblocks&#39;&#160;&#8212; is critical for ensuring faithful&#160;genome duplication.&#160;G-quadruplexes are higher-order nucleic acid structures that form in guanine-rich regions of DNA and have been shown to act as obstacles, interfering with genomic maintenance pathways. This study introduces a real-time, fluorescence microscopy-based method to observe DNA polymerase interactions with G-quadruplex structures. Short, primed DNA oligonucleotides containing a G-quadruplex were immobilized on functionalized glass coverslips within a microfluidic flow cell. Fluorescently labeled DNA polymerases were introduced, allowing their behavior and stoichiometry to be monitored over time. This approach enabled the observation of polymerase behavior as it was stalled by a G-quadruplex. Specifically, using fluorescently labeled yeast polymerase &#948;, it was found that upon encountering a G-quadruplex, the polymerase undergoes a continuous cycle of binding and unbinding. This single-molecule assay can be adapted to study interactions between various DNA-maintenance proteins and obstacles on the DNA substrate.

This protocol outlines a fluorescence microscopy-based single-molecule DNA replication assay, enabling real-time visualization of interactions between DNA polymerases and obstacles such as G-quadruplex structures.

A G-quadruplex DNA-affinity Approach for Purification of Enzymatically Active G4 Resolvase1

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