Name: uracil-dna glycosylase assay by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis
Uploaded: 2022-04-22T14:00:00
Description: Watch this Scientific Journal Video about Uracil-DNA Glycosylase Assay by Matrix-assisted Laser Desorption/Ionization Time-of-flight Mass Spectrometry Analysis at JoVE.com

We thank the NCFPB Integrated Core Facility for Functional Genomics (Taipei, Taiwan) and the NRPB Pharmacogenomics Lab (Taipei, Taiwan) for their technical support. This work was supported by the Ministry of Science and Technology, Taiwan, R.O.C. [grant number MOST109-2314-B-002 -186 to K.-Y.S., MOST 107-2320-B-002-016-MY3 to S.-Y.C., MOST 110-2320-B-002-043 to W.-h.F.]. H.-L. C. is a recipient of a doctoral fellowship from National Taiwan University. Funding for open access charge: Ministry of Science and Technology, R.O.C.

1. Substrate/template preparation
<ol>
	<li>Design uracil substrate/template duplex with a balanced G+C content of ~50 &#177; 10% and minimum melting temperature of 50 &#176;C for the duplex region. 
	NOTE: One nucleotide difference between 18 nt substrates and 19 nt templates (Table 1 and Figure 1) helps better MS signal interpretation and appropriate annealing. The template strand serves as complementary DNA to generate A-U or G-U mismatches (<stron...

This paper provides a detailed procedure for using a UDG MALDI-TOF MS assay method to directly detect AP-containing DNA products. The main advantages of this method are that uracil-containing substrates are label-free, scalable, easy to work with, and afford greater flexibility in substrate design.
The UDG supplier-recommended phenol/chloroform extraction enables inactivation of the enzyme to prevent degradation of product DNA. However, the phenol extraction protocol involves tedious phase-sep...

Although uracil is a normal base in RNA, it is a common and highly mutagenic lesion in genomic DNA. Uracil can arise from spontaneous/enzymatic hydrolytic deamination of a deoxycytidine. In each living cell, this deamination occurs 100-500 times per day under physiological conditions1,2. If these alterations are not repaired, there can be a change in the DNA sequence composition, causing mutation. As uracil in DNA prefers to pair with dATP during replication, if cytosine deaminates to uracil, in two replication events, there will be a new G:C to A:T transition mutation in half of the progeny DNA3.
Among the cellular strategies to maintain genetic stability, base excision repair (BER) is an essential mechanism that repairs damaged bases, such as uracil, in DNA4. BER is a highly evolutionarily conserved process. There are two general BER pathways: the short-patch pathway leading to a repair tract of a single nucleotide and the long-patch pathway that produces a repair tract of at least two nucleotides5. BER is a coordinated mechanism that occurs in several steps. The first step in BER is the enzymatic hydrolysis of the damaged nucleotide base by a damage-specific DNA glycosylase to generate an apurinic/apyrimidinic (AP) intermediate site6. This is followed by the cleavage of the sugar-phosphate backbone at the AP site by an endonuclease, clean-up of the DNA ends by a lyase, gap-filling by a DNA polymerase, and sealing the final nick by a ligase5.
Uracil-DNA glycosylase (UDG) hydrolyzes the uracil from uracil-containing DNA for BER in Escherichia coli. Conventional UDG assays using radiolabeled DNA involving different separation techniques6,7,8,9,10,11,12,13 are usually time-consuming, labor-intensive, with costly labeling reagents, complicated procedures, and requiring intensive training and practice to reduce risks of exposure to radioactive materials. Fluorometric oligonucleotide assays have been developed as a replacement for radioisotope labeling14, in addition to molecular beacons and F&#246;rster resonance energy transfer technology15,16,17,18,19,20. However, specific labeling is required for all the aforementioned methods. Recently label-free biosensors assays21,22,23 and colorimetric methods based on the formation of a G-quadruplex24,25,26 have been developed. However, multiple A:U pairs or specially designed sequences in the probes complicate enzyme unit definition.
MALDI-TOF MS is a technology that could be of great use in DNA analysis. Applications developed include single-nucleotide polymorphism genotyping27,28, modified nucleotide analysis29, and DNA repair intermediate identification30,31,32,33,34. MALDI-TOF MS should be readily adopted for DNA glycosylase analysis to detect AP-site-containing DNA products. However, AP-sites in DNA are prone to strand break under many experimental conditions33. A UDG assay is presented here using MALDI-TOF MS to directly measure AP site production without significant strand-break noise. This label-free method is easy to work with and has a high potential for the pharmaceutical application of DNA glycosylase inhibitor screening.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>2-Amino-2-hydroxymethyl-propane-1,3-diol (Tris base)</td>
			<td>J.T baker</td>
			<td></td>
			<td>Protocol 1,2</td>
		</tr>
		<tr>
			<td>Autoclaved deionized water</td>
			<td>MILLIPORE</td>
			<td></td>
			<td>Protocol 1,2</td>
		</tr>
		<tr>
			<td>EDTA</td>
			<td>J.T Baker</td>
			<td></td>
			<td>Protocol 1,2</td>
		</tr>
		<tr>
			<td>Gloves</td>
			<td>AQUAGLOVE</td>
			<td></td>
			<td>Protocol 1,2,3</td>
		</tr>
		<tr>
			<td>Hydrochloric acid (HCl)</td>
			<td>SIGMA</td>
			<td></td>
			<td>Protocol 1,2</td>
		</tr>
		<tr>
			<td>Ice bucket</td>
			<td>Taiwan.Inc</td>
			<td></td>
			<td>Protocol 2</td>
		</tr>
		<tr>
			<td>Low retention pipette tips(0.5-10 &#181;L)</td>
			<td>extra gene</td>
			<td></td>
			<td>Protocol 1,2</td>
		</tr>
		<tr>
			<td>Low retention pipette tips(1,250 &#181;L)</td>
			<td>national scientific supply co, Inc.</td>
			<td></td>
			<td>Protocol 1,2</td>
		</tr>
		<tr>
			<td>Low retention pipette tips(200 &#181;L)</td>
			<td>national scientific supply co, Inc.</td>
			<td></td>
			<td>Protocol 1,2</td>
		</tr>
		<tr>
			<td>MassARRAY</td>
			<td>&#160;Agena Bioscience, CA</td>
			<td></td>
			<td>Protocol 4, 5 
			Mass spectrometry control programs include Typer Chip Linker, SpectroACQUIRE, and Start RT Process.</td>
		</tr>
		<tr>
			<td>MassARRAY Nanodispenser</td>
			<td>AAT Bioquest, Inc.</td>
			<td>RS1000</td>
			<td>Protocol 3</td>
		</tr>
		<tr>
			<td>Microcentrifuge</td>
			<td>Kubota</td>
			<td></td>
			<td>Protocol 2</td>
		</tr>
		<tr>
			<td>Microcentrifuge</td>
			<td>Clubio</td>
			<td></td>
			<td>Protocol 2</td>
		</tr>
		<tr>
			<td>Microcentrifuge tube (1.5 mL)</td>
			<td>National scientific supply co, Inc.</td>
			<td></td>
			<td>Protocol 2</td>
		</tr>
		<tr>
			<td>Microcentrifuge tube rack</td>
			<td>Taiwan.Inc</td>
			<td></td>
			<td>Protocol 1,2</td>
		</tr>
		<tr>
			<td>Micropipette&#160; (P1000)</td>
			<td>Gilson</td>
			<td></td>
			<td>Protocol 1,2</td>
		</tr>
		<tr>
			<td>Micropipette&#160; (P2)</td>
			<td>Gilson</td>
			<td></td>
			<td>Protocol 1,2</td>
		</tr>
		<tr>
			<td>Micropipette (P10)</td>
			<td>Gilson</td>
			<td></td>
			<td>Protocol 1,2</td>
		</tr>
		<tr>
			<td>Micropipette (P100)</td>
			<td>Gilson</td>
			<td></td>
			<td>Protocol 1,2</td>
		</tr>
		<tr>
			<td>Micropipette (P200)</td>
			<td>Gilson</td>
			<td></td>
			<td>Protocol 1,2</td>
		</tr>
		<tr>
			<td>Micropipette (SL2)</td>
			<td>Rainin</td>
			<td></td>
			<td>Protocol 1,2</td>
		</tr>
		<tr>
			<td>Oligonucleotides</td>
			<td>Integrated DNA Technologies (Singapore)</td>
			<td></td>
			<td>Protocol 1,2</td>
		</tr>
		<tr>
			<td>Quest Graph IC50 Calculator (v.1)</td>
			<td>AAT Bioquest, Inc.</td>
			<td></td>
			<td>Fig. 4 
			https://www.aatbio.com/tools/ic50-calculator-v1</td>
		</tr>
		<tr>
			<td>Sodium hydroxide (NaOH)</td>
			<td>WAKO</td>
			<td></td>
			<td>Protocol 2</td>
		</tr>
		<tr>
			<td>SpectroCHIP array</td>
			<td>&#160;Agena Bioscience, CA</td>
			<td>#01509</td>
			<td>Protocol 3, 5</td>
		</tr>
		<tr>
			<td>Timer</td>
			<td>Taiwan.Inc</td>
			<td></td>
			<td>Protocol 2</td>
		</tr>
		<tr>
			<td>Typer 4.0 software</td>
			<td>&#160;Agena Bioscience, CA</td>
			<td>#10145</td>
			<td>Protocol 6 
			Typer 4.0 consists four programs including Assay Designer, Assay Editor, Plate Editor, and Typer Analyzer.</td>
		</tr>
		<tr>
			<td>UDG Reaction Buffer (10x)</td>
			<td>New England Biolabs, MA</td>
			<td>B0280S</td>
			<td>Protocol 2</td>
		</tr>
		<tr>
			<td>Uracil Glycosylase Inhibitor</td>
			<td>New England Biolabs, MA</td>
			<td>M0281S</td>
			<td>Protocol 2</td>
		</tr>
		<tr>
			<td>Uracil-DNA Glycosylase</td>
			<td>New England Biolabs, MA</td>
			<td>M0280L</td>
			<td>Protocol 2</td>
		</tr>
		<tr>
			<td>UV-VISBLE spectrophotometer UV-1601</td>
			<td>SHIMADZU</td>
			<td></td>
			<td>Protocol 1</td>
		</tr>
		<tr>
			<td>Water bath</td>
			<td>ZETA ZC-4000 (Taiwan.Inc)</td>
			<td></td>
			<td>Protocol 2</td>
		</tr>
	</tbody>
</table>

uracil-dna glycosylase assay by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis

Uracil-DNA glycosylase (UDG) is a key component in the base excision repair pathway for the correction of uracil formed from hydrolytic deamination of cytosine. Thus, it is crucial for genome integrity maintenance. A highly specific, non-labeled, non-radio-isotopic method was developed to measure UDG activity. A synthetic DNA duplex containing a site-specific uracil was cleaved by UDG and then subjected to Matrix-assisted Laser Desorption/Ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis. A protocol was established to preserve the apurinic/apyrimidinic site (AP) product in DNA without strand break. The change in the m/z value from the substrate to the product was used to evaluate uracil hydrolysis by UDG. A G:U substrate was used for UDG kinetic analysis yielding the Km = 50 nM, Vmax = 0.98 nM/s, and Kcat = 9.31 s-1. Application of this method to a uracil glycosylase inhibitor (UGI) assay yielded an IC50 value of 7.6 pM. The UDG specificity using uracil at various positions within single-stranded and double-stranded DNA substrates demonstrated different cleavage efficiencies. Thus, this simple, rapid, and versatile MALDI-TOF MS method could be an excellent reference method for various monofunctional DNA glycosylases. It also has the potential as a tool for DNA glycosylase inhibitor screening.

Templates and substrates 
Taking synthetic oligonucleotides with U in the center (U+9) paired with a G template as an example (Figure 1A), a blank control of equimolar amounts of template and uracil-containing substrate can be used for quality control of synthetic oligonucleotide purity (Figure&#160;1B; the signals match the designated m/z and the low background noise). For the MS data analysis, the peak heights were measured (<strong class...

Watch this Scientific Journal Video about Uracil-DNA Glycosylase Assay by Matrix-assisted Laser Desorption/Ionization Time-of-flight Mass Spectrometry Analysis at JoVE.com

Uracil-DNA Glycosylase Assay by Matrix-assisted Laser Desorption/Ionization Time-of-flight Mass Spectrometry Analysis

A non-labeled, non-radio-isotopic method to assay uracil-DNA glycosylase activity was developed using MALDI-TOF mass spectrometry for direct apurinic/apyrimidinic site-containing product analysis. The assay proved to be quite simple, specific, rapid, and easy to use for DNA glycosylase measurement.

Uracil-DNA glycosylase (UDG) is a key component in the base excision repair pathway for the correction of uracil formed from hydrolytic deamination of ...

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