Presentation on theme: "Western Analysis Laboratory procedure that allows you to:"— Presentation transcript:
1 Western Analysis Laboratory procedure that allows you to: 1. Verify the expression of a protein2. Determine the relative amount of a protein present in different samples3. Analyze protein-protein interactions
2 Two Main Types of Westerns 1. Denaturing (Most Commonly Used)- SDS-PAGE2. Non-Denaturing- Native PAGE
3 - + SDS-PAGE Western Blot Method - - - - - - - - Cell Lysis by Detergents and SonicationCells in CultureCell RemovalHuman Cells Containing Protein-SDS or LDS--Heat Denaturation of Proteins-Detergents Bind Proteins---Load Proteins on Gel+--Proteins Separate by SizeApply Electric Current
4 --Transfer or Blot Protein from Gel to Nitrocellulose and/or PVDF Membrane--Block Membrane with Non-Specific Proteins--Incubate Membrane with 1o Antibody1o Antibody is a Rabbit Anti-Human b-Actin Antibody1o Antibody Binds Antigen (i.e. Protein of Interest)Non-Specific Proteins Bind to Unbound Regions of Membrane
5 - - - Add HRP-Conjugated 2o Antibody HRP Luminol Light Detected by Film2o Antibody is a Goat Anti-Rabbit-HRP-Conjugated AntibodyAdd Chemiluminescent Substrate
6 Magic Mark XP Western Protein Standard kDa605045b-Actin403020Invitrogen.com
7 Antibodies can be purchased from a wide array of vendors Antibodies can be purchased from a wide array of vendors. This is the information sheet from the Cell Signaling beta actin antibody that we will be using for our western blots.
8 We will be using 4-12% Bis Tris Gels today because our protein of interest is 45 kDa in size. For larger proteins (>100 kDa) this type of gel would not be appropriate because the resolution of large proteins on a 4-12% Bis Tris gel is poor.
9 Magic Mark XP Western Protein Standard kDa605045b-Actin403020Invitrogen.comQUESTIONIf we wanted to detect another human protein that was 60 kDa on this blot at the same time as beta actin could we?Why would it be wise to use a primary antibody against this protein that was generated in a rabbit?
10 Some Drawbacks of Western Blotting 1. Many steps where errors can occur2. Large amount of sample needed (5-50 mg)3. Accurate quantitation is very difficultMention ELISA here and its benefits: Accurate quantitation possible with very little sample, shorter protocol with fewer steps where errors can occur.4. Time consuming protocol
11 Western Blot Protocol Sample Preparation A) Add 10 mg of protein to 5 ml of 4X LDS Loading Buffer plus 2.5 ml of 10X Reducing Agent. Then add purified water to a total volume of 25 ml.For example: If your total protein concentration is 2.0 mg/ml, you would need 5 ml of total protein to equal 10 mg. So you would mix:5 ml of protein5 ml of 4X LDS Loading Buffer2.5 ml 10X Reducing Agent12.5 ml purified water.B) Heat sample mixture at 70oC for 10 minutes.
12 XCell SureLock Mini-Cell, Invitrogen 2. ElectrophoresisA) While protein samples are heating, assemble electrophoresis unit.DemonstrationXCell SureLock Mini-Cell, InvitrogenInvitrogen.comLoad Gel-Molecular weight marker and protein samplesDemonstrationInvitrogen.com
13 C) Add 500 ml Antioxidant to top chamber to maintain proteins in a reduced state and ensure optimal band sharpness.D) Run gel at 180V for 45 minutes
14 Demonstration 3. Transfer A) Soak marked (for orientation) nitrocellulose (or PVDF) membrane in transfer buffer containing 10% Methanol at least 10 minutes prior to transfer.When gel run is complete, turn off power source, remove gel from pre-cast plates, place transfer buffer-soaked filter paper sheet on top of gel, remove gel from plate, and place on top of membrane blotting pads that have been removed of bubbles.C) Place membrane on top of gel and cover with another transfer buffer-soaked filter paper sheet and blotting pads to fill the transfer chamber.DemonstrationInvitrogen.comBlotting PadD) Add 500 ml Antioxidant and run transfer at 30V for 1 hour.
15 4. BlockingA) Remove membrane from transfer chamber and incubate in 5% Blotto [5% powdered milk in TBS-Tw (1X TBS, 0.1% Tween 20)] at room temperature for 30 minutes with slow shaking.5. Primary Antibody IncubationA) Prepare a 1:1000 dilution of primary antibody (Rabbit Anti-Human b-Actin) in 5% Blotto.B) Incubate membrane in primary antibody solution overnight at 4oC with gentle rocking.
16 Why are we using Goat Anti-Rabbit IgG-HRP as our secondary antibody? 6. Membrane WashingA) Wash membrane 3 x 5 minutes each in TBS-Tw with gentle shaking at room temperature.7. Secondary Antibody IncubationA) Prepare a 1:5000 dilution of secondary antibody (Goat Anti-Rabbit IgG-HRP) in 5% Blotto.B) Incubate membrane in secondary antibody solution for 30 minutes at room temperature with gentle shaking.QUESTIONWhy are we using Goat Anti-Rabbit IgG-HRP as our secondary antibody?8. Repeat Membrane Washing – See step 6
17 9. Visualization of Protein of Interest A) Place membrane protein side up on saran wrap on a flat surface.B) Quickly add 50 ml of ECL solution B to 2 ml of ECL solution A, mix, and add directly to membrane.C) Incubate in the dark for 3-5 minutes, remove excess solution, and place membrane protein side down onto a new piece of saran wrap.D) Close saran wrap around membrane, tape to film cassette and expose film in the dark room for 30 seconds to 1 minute.E) Develop film & identify protein of interest.
18 Magic Mark XP Western Protein Standard kDa605045b-Actin403020