Engineered Polymerases with Altered Substrate Specificity: Expression and Purification

Ali Nikoomanzar1, Matthew R. Dunn1, John C. Chaput1

1 Department of Pharmaceutical Sciences. University of California, Irvine, California
Publication Name:  Current Protocols in Nucleic Acid Chemistry
Unit Number:  Unit 4.75
DOI:  10.1002/cpnc.33
Online Posting Date:  June, 2017
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Polymerase engineering is making it possible to synthesize xeno‐nucleic acid polymers (XNAs) with diverse backbone structures and chemical functionality. The ability to copy genetic information back and forth between DNA and XNA has led to a new field of science known as synthetic genetics, which aims to study the genetic concepts of heredity and evolution in artificial genetic polymers. Since many of the polymerases needed to synthesize XNA polymers are not available commercially, researchers must express and purify these enzymes as recombinant proteins from E. coli. This unit details the steps needed to express, purify, and evaluate the activity of engineered polymerases with altered substrate recognition properties. The protocol requires 6 days to complete and will produce ∼20 mg of pure, nuclease‐free polymerase per liter of E. coli bacterial culture. © 2017 by John Wiley & Sons, Inc.

Keywords: aptamer; polymerase; protein expression and purification; xeno‐nucleic acid (XNA)

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Table of Contents

  • Introduction
  • Strategic Planning
  • Basic Protocol 1: Polymerase Expression in E. coli
  • Basic Protocol 2: Polymerase Purification and Testing
  • Reagents and Solutions
  • Commentary
  • Literature Cited
  • Figures
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Basic Protocol 1: Polymerase Expression in E. coli

  • 70% ethanol
  • 1.5% LB‐ampicillin (100 μg/mL) agar plate (see recipe)
  • 100 mg/mL ampicillin (see recipe)
  • Polymerase expressing E. coli cells (glycerol stock)
  • Luria‐Bertani (LB) medium (see recipe)
  • 1 M IPTG (see recipe)
  • Lysozyme (0.1 mg/mL), optional
  • Cell resuspension buffer (see recipe)
  • 10% (v/v) polyethyleneimine (PEI) (see recipe)
  • Ammonium sulfate powder (Sigma)
  • Bunsen burner
  • Inoculating loops
  • Permanent marker
  • 15º and 37ºC incubators (with and without shaking)
  • 500‐mL and 2‐L baffled flasks, sterile
  • Aluminum foil
  • UV cuvettes
  • UV spectrophotometer
  • Refrigerated centrifuge and rotors JLA 9.1 and JA 25.50 (Beckman)
  • 1‐L centrifuge jars
  • 10‐ and 50‐mL disposable pipets
  • 40‐mL centrifuge tubes
  • Sonicator
  • 80ºC water bath or hot plate

Basic Protocol 2: Polymerase Purification and Testing

  • Nickel buffer A (see recipe)
  • Nickel buffer B (see recipe)
  • 20% ethanol
  • Recombinant polymerase protein pellet (see protocol 1)
  • 4× Nu‐PAGE loading buffer
  • Mini‐PROTEAN TGX Stain‐Free gel
  • 1× TGS running buffer (see recipe)
  • Unstained protein ladder (ThermoFisher)
  • Nickel elution diluton buffer (see recipe)
  • Heparin buffer A (see recipe)
  • Heparin buffer B (see recipe)
  • Nuclease‐free water
  • 10× ThermoPol buffer (NEB)
  • IR800 PBS8 primer (Integrated DNA Technologies): 5′‐/5IRD800//iSp18/GTCCCCTTGGGGATACCACC
  • L11 Library (Integrated DNA Technologies):
  • 1 mM each tNTP mix (tATP, tTTP, tCTP, tGTP)
  • Polymerase dilution buffer (see recipe)
  • Polymerase
  • 10 mM MnCl 2 (see recipe)
  • Stop buffer (see recipe)
  • 20% Urea‐PAGE solution (see recipe)
  • 10% (w/v) ammonium persulfate (APS, see recipe)
  • N,N,N,N′,Tetraethylmethylenediamine (TEMED, Pierce)
  • Acrylamide concentrate (see recipe, also available from National Diagnostics)
  • Acrylamide diluent (see recipe, also available from National Diagnostics)
  • 10× TBE buffer (see recipe)
  • Absolute ethanol (Sigma)
  • 70% ethanol, −20°C
  • Manganese hexahydrate (Sigma)
  • 0.1 M NaOH
  • 5 mL HisTrap HP Resin (GE Healthcare)
  • 40‐mL centrifuge tubes
  • Refrigerated centrifuge
  • 50‐mL conical tubes
  • 5‐mL Nickel HP columns (GE)
  • FPLC system (AKTA)
  • Superloop (size varies)
  • Fraction collector (AKTA)
  • 1.5‐mL microcentrifuge tubes (Eppendorf)
  • 75º and 90ºC heating blocks
  • Electrophoresis apparatus (BioRad)
  • Power supply
  • Geldoc (BioRad)
  • 5‐mL Heparin HP resin columns (GE Healthcare)
  • Spectrophotometer (Nanodrop)
  • 200‐μL PCR tubes
  • Thermal cycler
  • Gel plates (19.7 × 16– and 19.7 × 18.5–cm)
  • Spacers (1.5‐mm thick)
  • Comb (20‐well)
  • 50‐mL beaker
  • Magnetic stir bar and stir plate
  • PAGE electrophoresis apparatus
  • 50‐mL plastic syringe
  • Vortex
  • Refrigerated microcentrifuge
  • LICOR Odyssey cLX imager
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Literature Cited

Literature Cited
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