Altman:Protocols/Single Molecule Assays/single bead

Department of Physics, Willamette University

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Single Bead Optical Trapping Assay

Before you start

• Prepare an aliquot of α-GFP/10 (5 μL of α-GFP 0.5 mg/mL stock + 45 μL AB)

Make α-GFP beads

1. Take 10 μL of 1-μm diameter carboxylated beads

2. Wash beads 3x in AB All wash steps should be performed as follows

• Spin down beads in a benchtop centrifuge at max speed (14k rpm) for 1-2 minutes
• Carefully, pull off the supernatant
• Re-suspend beads in AB

3. Add 20 μL of pre-mixed mixture consisting of 19 μL α-GFP/10 antibody + 1 μL TMR-BSA stock (6 mg/mL)

4. Let mixture sit for 5 minutes

5. Wash 10x in ABSA, re-suspending the beads in 10 μL of ABSA

Flow-through volumes are typically 10-15 μL

1. Make MB mixture:

ABSA	24 μL
motor dilution	0.5 μL
α-GFP beads	0.5 μL

• Allow this mixture to incubate for ~15 minutes

2. Make a flow cell with a nitrocellulose-coated coverslip

3. Flow in NaV/10 stock

4. Let cell incubate for 2 minutes

5. Wash with ABSA

6. Flow in actin dilution

• Typically Actin/10 or Actin/20

7. Wash with ABSA immediately

8. Flow in GO-Juice

2.5 μL MB mixture 1 μL GOC stock (50x) 1 μL glucose/β-mercaptoethanol stock (50x) 0.5 μL CPK (100x) 0.5 μL PCr (100x) 1 μL ATP dilution (50x) 43.5 μL AB

RECIPES

Buffer #1

	50 uL Buffer #1
50x GOC stock	2 μL
100x CPK stock	1 μL
100x ATP stock	1 μL
AB	46 μL

Buffer #2

	50 μL Buffer #2
50x Glu/B stock	2 μL
100x PCr stock	1 μL
AB	47 μL

GO-Juice

	20 μL GO-Juice
Buffer #1	10 μL
Buffer #2	10 μL