Drummond:Protein Isolation

Isolating total, soluble and insoluble protein fractions from isotopically labeled strains of S. cerevisiae

Day -2

• For each strain, inoculate a 3 mL YPD pre-culture of YPD with a single yeast colony and incubate overnight at 30⁰C with shaking or rotation.

Day -1

• Inoculate 50 mL of synthetic complete medium (SC) with labeled amino acids with 3 µL of the overnight pre-culture and incubate for 18 h at 30⁰ C with shaking in a 500 mL baffled flask.

Day 0

Cell preparation

• Grow 50mL culture of cells to a density of 4×10⁶ cells/mL (OD₆₀₀ ≈ 0.4).

While cells are growing, make solutions: SPB, WB, IPB.

• Transfer 1.4×10⁸ cells to a 50mL conical tube (35 mL of a 4×10⁶ cells/mL culture)
• Spin at 3000g for 1 minute.
• Gently decant and discard supernatant.
• Resuspend cell pellet in 1.4mL ice-cold Tris (50mM, pH 8.5) and transfer to 1.5mL microcentrifuge tube.
• Spin at 20,000g for 15 seconds.
• Discard supernatant, clear final bit of supernatant with a hard flick.
• Freeze pellet in liquid nitrogen.

Lysis

• For each strain, rack a 2mL flat or round-bottom microcentrifuge tube in LN2 and place a 7mm stainless-steel ball (Retsch) inside. Put some LN2 in tube to speed cooling of ball (ultimately we want all the LN2 to boil away).
• Resuspend frozen pellet in 50 µL SPB.
• Drip resuspended pellet onto upper wall of tube containing ball. Goal is to get a nugget of frozen material on the wall, and to avoid dripping the material around the ball and thus freezing the ball to the bottom of the tube.
• When all LN2 has boiled out of tube (listen -- if any popping or hissing, keep waiting), snap tube closed. Keep in LN2. (Any remaining LN2 in tube will cause tube to explode open and fire the stainless steel ball into your iPad, brain, colleague, or other important equipment.)
• Agitate for 4×90 seconds at 30 Hz in a Retsch Mixer Mill MM400, returning sample holder to LN2 between sessions. Complete lysis produces fine snowy powder in the tube.
• Add 450 μL SPB to tube, and extract ball with a magnet.
• Remove 500 μL sample and to fresh 1.5mL microcentrifuge tube.

Soluble fraction extraction

Buffer recipes

Stock solutions

• 200mM DTT
• 100mM PMSF
• 4M NaCl
• 1M Tris-HCl, pH 8.5
• 20% SDS (w/v)

Soluble Protein Buffer, pH 8.5 (SPB)

(50mM Tris-HCl, 500mM NaCl, 1:100 protease inhibitors)

Start by making 50 mL SPB stock solution:

• 2.5 mL 1M Tris-HCl, pH 8.5
• 6.25 mL 4M NaCl
• 41.25 mL protease-free H₂O

Then mix 9.8 mL of SPB stock solution with 100 µL 100mM PMSF and 100uL protease inhibitors to make 10mL SPB.

For protease inhibitors, we use:

• AEBSF, HCl, MW=239.5, targets serine proteases, 100 mM
• E-64, MW=357.4, targets cysteine proteases, 1.5 mM
• Pepstatin A, MW=685.9, targets aspartic proteases, 2 mM
• o-Phenanthroline, MW=198.2, targets metalloproteases, 500 mM

This mixture is commercially available as Calbiochem protease inhibitor cocktail set IV, or BioVision EZBlock protease inhibitor cocktail IV.

Wash Buffer (WB)

(50mM Tris-HCl, 150mM NaCl, 1:100 protease inhibitors) Same as SPB, but with reduced salt to limit pellet loss.

Start by making 50 mL WB stock solution:

• 2.5 mL 1M Tris-HCl, pH 8.5
• 1.875 mL 4M NaCl
• 45.625 mL protease-free H₂O

Then mix 9.8 mL of WB stock solution with 100 µL 100mM PMSF and 100µL protease inhibitors to make 10mL WB.

Insoluble Protein Buffer, pH 8.5 (IPB)

(50mM Tris-HCl, 150mM NaCl, 8M urea, 2% SDS, 1mM PMSF, 2mM DTT, 1:1000 protease inhibitors) Make fresh before each use. Note that at 8M, urea occupies ~72% of the solution volume, so that 4.8g urea occupies 7.2mL of a 10mL solution. Do not use 500mM NaCl in this solution, as it loosens pellets and causes sample loss.

• 8M urea
• 2% SDS
• 50mM Tris pH 8.5
• 150mM NaCl
• 1mM PMSF
• 20 μL 200mM DTT
• 1:1000 protease inhibitors (see above. higher concentrations may crash out.)

Use 500μL IPB per sample, and note that foaming will make ~25% of the solution unusable.

2mL IPB (~2 samples)	13mL IPB (~10 samples)
0.96g urea 683 μL H2O 200 μL 20% SDS (w/v) 100 μL 1M Tris pH 8.5 75 μL 4M NaCl 20 μL 100mM PMSF 20 μL 200mM DTT 2 μL protease inhibitors	6.24g urea 5.58 mL H2O 1.3 mL 20% SDS (w/v) 650 μL 1M Tris pH 8.5 488 μL 4M NaCl 130 μL 100mM PMSF 130 μL 200mM DTT 13 μL protease inhibitors

6x Soluble Protein Loading Buffer, pH 6.8 (SPLB)

(50 mM Tris-HCl pH 8.5, 10% SDS, 0.05% bromophenol blue, 30% glycerol, 5% β-mercaptoethanol [βME])

Start by making 9 mL 6x SPLB Stock Solution:

• 0.5 mL 1M Tris-HCl, pH 8.5
• 1 g SDS
• 5 mg bromophenol blue
• 3 mL glycerol
• 5.5 mL protease-free water

Then mix 712.5 µL of 6x SPLB stock solution with 37.5 µL of 14.3M βME immediately before use.

6x Insoluble Protein Loading Buffer, pH 6.8 (IPLB)

(50 mM Tris-HCl, 0.05% bromophenol blue, 30% glycerol, 5% βME)

Start by making 9 mL 6x SPLB Stock Solution:

• 0.5 mL 1M Tris-HCl, pH 6.8
• 5 mg bromophenol blue
• 3 mL glycerol
• 5.5 mL protease-free water

Then mix 475 µL of 6x SPLB stock solution with 25 µL 14.3M βME immediately before use.