Difference between revisions of "20.109(S21):M2D1"

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(Purify PF3D7_1351100 from cell lysate)
(Purify TDP43-RRM12 from cell lysate)
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#To equilibrate the Ni-NTA affinity column for the elution step, add 2 mL of HRV 3C buffer.
 
#To equilibrate the Ni-NTA affinity column for the elution step, add 2 mL of HRV 3C buffer.
 
#Allow the HRV 3C buffer to pass through then cap the bottom of the column.
 
#Allow the HRV 3C buffer to pass through then cap the bottom of the column.
#Add 10 &u;L of HRV 3C protease to 1 mL of HRV 3C buffer.
+
#Add 10 μL of HRV 3C protease to 1 mL of HRV 3C buffer.
 
#To elute the TDP43-RRM12 protein from the affinity column, add the HRV 3C protease / buffer to the Ni-NTA affinity column.
 
#To elute the TDP43-RRM12 protein from the affinity column, add the HRV 3C protease / buffer to the Ni-NTA affinity column.
 
#Completely resuspend the slurry in the Ni-NTA affinity column by pipetting up and down using a P1000 pipet.
 
#Completely resuspend the slurry in the Ni-NTA affinity column by pipetting up and down using a P1000 pipet.

Revision as of 19:37, 21 January 2021

20.109(S21): Laboratory Fundamentals of Biological Engineering

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Spring 2021 schedule        FYI        Assignments        Homework        Communication |        Accessibility

       M1: Antibody engineering        M2: Drug discovery        M3: Protein engineering       


Introduction

The TDP43 protein is encoded by the TARDBP gene. The entire sequence of the gene is 1242 bases (the protein is 414 amino acids) and composed of four domains: the N-terminal involved in dimerization / oligomerization, two RNA recognition motifs (RRM1 & RRM2) which are required for RNA / DNA binding, and the C-terminal domain involved in protein-protein interactions. In this module, we are interested in ligands that bind the RRM1 and RRM2 domains. For this module, the RRM1 and RRM2 portion of TDP43 was cloned into an expression vector to enable the purification of this segment of the protein. To induce production of TDP43-RRM12 protein from the expression plasmid, a lactose-analogue isopropyl β-D-1-thiogalactopyranoside (IPTG) and arabinose was used to induce expression in BL21-A1 E. coli bacterial cells.

Sp17 20.109 M1D2 lac operon.png
Sp17 20.109 M1D2 lactose vs IPTG.png
The lac operon is composed of four genes: lacI, lacZ, lacY, and lacA. When lactose is absent, LacI (the protein encoded by lacI) binds to the operator sequence (O) upstream of lacZYA. In the presence of lactose, LacI and lactose form a complex which relieves repression of lacZYA transcription. LacZ is a β-galactosidase that cleaves lactose resulting in glucose and galactose. LacY, a β-galactoside permease, facilitates the transport of lactose across the cell membrane, and LacA, a β-galactoside transacetylase, transfers an acetyl group from acetyl-CoA to β-galactosides.

Use of IPTG to induce protein expression is based on the native lac operon used for lactose metabolism in bacterial cells. The native lac operon is a powerful tool in engineering protein expression systems because it enables researchers to control gene expression using inducer molecules. The lacZYA genes are only expressed when lactose is present. If a gene of interest is cloned downstream of the operator sequence, the expression of this gene can be controlled by LacI repression and lactose derepression. To further control the system for protein expression, IPTG is used as a lactose-analog as it is not metabolized by the cells.

Today you will isolate the expressed TDP43-RRM12 protein (remember that the isolated product is actually a truncated version of the TDP43 protein and contains only RRM1 and RRM2!) from the bacterial cells. The TDP43-RRM12 sequence was cloned into an expression vector that contains six histidine codons where the 5' end of the DNA sequence is inserted. Our resultant protein is therefore marked by the presence of these additional encoded residues, also referred to as His-tagged. Histidine has several interesting properties, notably its near-neutral pKa, and His-rich peptides are promiscuous binders, particularly to metals. As an example, histidine side chains help coordinate iron molecules in hemoglobin.

To purify the TDP43-RRM12 proteins present in the bacterial cell, you will use a nickel-agarose resin. The 6xHis-tag on the PF3D7_1351100 protein will bind to the nickel-coated resin, while the other cellular protein will pass through the resin. Remember, the BL21-A1 cells are not only producing the TDP43-RRM12 protein, but also the proteins needed for cellular function and survival. Imidazole is a compound that is also able to bind to nickel and washing the resin with a low concentration solution promotes competition for binding between the imidazole and bound proteins for the nickel-coated resin. Proteins that are non-specifically bound will have a lower affinity for the nickel than imidazole and be washed from the column, whereas the 6xHis-tagged PF3D7_1351100 will remain adhered to the nickel-agarose resin. To elute the TDP43-RRM12 protein from the nickel-coated resin, an enzyme will be used to cleave the protein from the nickel-agarose resin.

Schematic of affinity separation process. For purification, agarose beads (yellow) are coated with nickel (green). When cell lysate is added to the nickel-coated agarose beads, His-tagged protein of interest (blue) adheres to the beads and other proteins in the lysate (orange) are washed from the beads.

Protocols

Part 1: Induce expression of TDP43-RRM12

To ensure the steps included below are clear, please watch the video tutorial linked here: [Bacterial Induction]. The steps are detailed below so you can follow along!

  1. Inoculate 5 mL of LB media containing 50 μg/mL ampicillin with a colony of BL21(A1) cells transformed with pET_MPB_SNAP_TDP43-RRM12.
  2. Incubate the culture overnight at 37 °C with shaking at 220 rpm.
  3. Dilute the overnight culture 1:10 in 50 mL of fresh LB media containing 50 μg/mL ampicillin.
  4. Incubate at 37 °C until the OD600 = 0.6 with shaking at 220 rpm, approximately 4 hours.
  5. To induce TDP43-RRM12 protein expression, add IPTG to a final concentration of 1 mM and arabinose to a final concentration of 0.2%.
  6. Incubate 37 °C with shaking at 100 rpm for 2.5 hr.
  7. To harvest the cells, centrifuge the culture at 3000 g for 15 min at 4 °C.
  8. Cell pellets were flash frozen in liquid nitrogen, then stored at -80 °C until used for purification.

In your laboratory notebook, complete the following:

  • Calculate the volume of ampicillin stock that was added to the LB broth in Step #1. In Step #3.
    • Concentration of kanamycin stock = 50 mg/mL.
  • Calculate the volume of IPTG stock that was added to the LB broth in Step #5.
    • Concentration of IPTG stock = 100 mM.
  • Calculate the volume of arabinose stock that was added to the LB broth in Step #5.
    • Concentration of arabinose stock = 20%.

Part 2: Purify PF3D7_1351100 protein

To ensure the steps required for purifying the TDP43-RRM12 protein are clear, the Instructor will provide a live demonstration of this process. You should include notes regarding the procedure in your laboratory notebook!

Lyse BL21(A1) cells expressing pET_MBP_SNAP_TDP43-RRM12

  1. Retrieve the BL21(A1) pET_MBP_SNAP_TDP43-RRM12 cell pellet from the -80 °C freezer and leave it on your bench to thaw.
  2. Add the cell lysis buffer and components to each cell pellet.
    • B-Per bacterial extraction reagent at 4 mL / g of cell pellet
    • lysozyme at 2 μL / mL of B-Per bacterial extraction reagent
    • DNAse I at 2 μL / mL of B-Per bacterial extraction reagent
    • AEBSF to a final concentration of 1 mM
  3. Solubilize the cell pellet in lysis buffer and vortex to mix.
  4. Incubate cell pellet in lysis buffer at room temperature for 15 min.
  5. To pellet the cell debris, centrifuge the lysate at 15,000 g for 30 min at 4 °C.
  6. Complete the next section (Prepare Ni-NTA affinity column) during the centrifugation.

Prepare Ni-NTA affinity column

  1. Obtain a 500 μL aliquot of 50% slurry (Ni-NTA resin) and mix the slurry by inverting the tube several times.
    • The slurry is the Ni-NTA column matrix!
  2. Centrifuge the slurry for 30 sec then remove the supernatent.
  3. To wash the slurry, add 500 μL of 1X PBS and invert the tube 3 times.
  4. Add the slurry to the column and allow the 1X PBS to run through the column.
    • Be sure a beaker is placed under the column to collect the waste!
  5. When the PBS has flowed through, cap the bottom and the top of the column until you are ready to add the cell lysate.

Purify TDP43-RRM12 from cell lysate

  1. Transfer the supernatent from the centrifuged cell lysate to a fresh microcentrifuge tube.
    • Label the microcentrifuge tube containing the cell pellet as "pellet" and give it to the Instructor! This pellet will be used later when protein expression and purity are examined.
  2. Aliquot 30 μL of the supernatent (from Step #1) to a fresh microcentrifuge tube.
    • Label the microcentrifuge tube containing the aliquot as "lysate" and give it to the Instructor! This aliquot will be used later when protein expression and purity are examined.
  3. To the remaining cell lystate, add 10 μL of SnapTag substrate then add DTT to a final concentration of 1 mM.
    • Note: The SnapTag substrate labels the TDP43-RRM12 protein with a 647 nm fluorophore at the SNAP sequence that was incorporated into the protein sequence as part of the cloning strategy.
  4. Pipet the cell lysate containing SnapTag / DTT into the prepared Ni-NTA affinity column.
    • Be sure that the bottom of the column is capped!
  5. Attach the cap to the top of the column and cover with aluminum foil to protect the protein from light.
  6. Incubate the covered Ni-NTA affinity column on the nutator for 2 hrs at 4 °C.
  7. Following the incubation, clamp the affinity column into the ring stand.
  8. Collect the flowthrough from the affinity column.
    • Hold a microcentrifuge tube under the column, then remove the bottom cap from the column and collect the liquid that leaves the column.
    • Label the microcentrifuge tube as "flowthrough" and give it to the Instructor! This aliquot will be used later when protein expression and purity are examined.
  9. To wash the Ni-NTA affinity column, add 7.5 mL of wash buffer.
    • Hold a microcentrifuge tube under the column, then remove the bottom cap from the column and collect ~250 μL of the liquid that leaves the column.
    • Label the microcentrifuge tube as "wash" and give it to the Instructor! This aliquot will be used later when protein expression and purity are examined.
  10. To equilibrate the Ni-NTA affinity column for the elution step, add 2 mL of HRV 3C buffer.
  11. Allow the HRV 3C buffer to pass through then cap the bottom of the column.
  12. Add 10 μL of HRV 3C protease to 1 mL of HRV 3C buffer.
  13. To elute the TDP43-RRM12 protein from the affinity column, add the HRV 3C protease / buffer to the Ni-NTA affinity column.
  14. Completely resuspend the slurry in the Ni-NTA affinity column by pipetting up and down using a P1000 pipet.
  15. Add the cap to the top of the Ni-NTA affinity column and wrap in aluminum foil.
  16. Incubate the covered Ni-NTA affinity column on the nutator overnight at 4 °C.
  17. Following the incubation, clamp the affinity column into the ring stand.
  18. To collect the purified TDP43-RRM12 protein, hold a microcentrifuge tube under the column, then remove the bottom cap from the column and collect the entire 1 mL of the liquid that leaves the column.
    • Label the microcentrifuge tube as "elution" and give it to the Instructor! This aliquot will be used later when protein expression and purity are examined.
  19. Lastly, resuspend the slurry from the Ni-NTA affinity column in 250 μL 1X PBS and transfer to a fresh microcentrifuge tube.
    • Label the microcentrifuge tube as "slurry" and give it to the Instructor! This aliquot will be used later when protein expression and purity are examined.

In your laboratory notebook, complete the following:

  • At several steps in the protein purification procedure, samples are collected that will be used later when protein expression and purity are examined. Consider why each of the samples listed below are saved as controls to measure the success of the purification.
    • The pellet from Step #1.
    • The lysate from Step #2.
    • The flowthrough from Step #8.
    • The wash from Step #9.
    • The slurry from Step #19.
  • What is occurring during the incubation in Step #6? In Step #16?

Reagents list

  • Terrific broth (TB) (from RPI)
  • kanamycin (from Sigma)
  • isopropyl β-d-1-thiogalactopyranoside (IPTG) (from Sigma)
  • 2x B-Per bacterial protein extraction reagent (from ThermoFisher)
  • lysozyme (from Sigma)
  • DNase I (from Sigma)
  • 4-(2-aminoethyl)benzenesulfonyl fluoride (AEBSF) (from Sigma)
  • phosphate saline buffer (PBS) (from VWR)
  • Ni-NTA agarose (from Qiagen)
  • Wash buffer: 100 mM HEPES (pH = 7.4), 500 mM NaCl, 10 mM imidazole
  • Elution buffer: 100 mM HEPES (pH = 7.4), 500 mM NaCl, 250 mM imidazole
  • imidazole (from Sigma)

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