Arf-like protein 1 (Arl1) is a member of the Arf family of regulatory GTPases, within the Ras superfamily of GTPases, and with highly conserved orthologs throughout eukaryotes. Arl1 is essential for early embryonic development in Drosophila and in Caenorhabditis elegans. Arl1 is most similar in primary sequence, cellular location, and function (regulation of membrane traffic) to Arf1–6 and even shares several common binding partners. In addition to its function in membrane traffic at the Golgi/trans-Golgi network, there are reports indicating a possible role for Arl1 in ion homeostasis in yeast.

Currently there is no direct assay to measure the activation of Arl1 GTPases.

The Arl1 Activation Assay Kit is based on the configuration-specific monoclonal antibody that specifically recognizes Arl1-GTP, but not Arl1-GDP. Given the high affinity of monoclonal antibodies to their antigens, the activation assay could be performed in a short time. This assay provides the reliable results with consistent reproducibility.

1. Anti-Arl1-GTP Mouse Monoclonal Antibody (Cat. # 26924): One vial – 35 µL (1 mg/ml) in PBS, pH 7.4, containing 50% glycerol. This antibody specifically recognizes Arl1-GTP from all vertebrates.

2. Protein A/G Agarose (Cat. # 30301): One vial – 600 µL of 50% slurry.

3. 5X Assay/Lysis Buffer (Cat. # 30302): One bottle – 30 mL of 250 mM Tris-HCl, pH 8, 750mM NaCl, 50 mM MgCl2, 5 mM EDTA, 5% Triton X-100.

4. Anti-Arl1 Mouse monoclonal Antibody (Cat. # 26056): One vial – 50 µL (1mg/mL) in PBS, pH 7.4, contained 50% glycerol.

5. 100X GTPγS (Cat. # 30303): One vial – 50 µl at 10 mM, use 5 µL of GTPγS for  GTP-labeling of 0.5 mL of cell lysate.

6. 100X GDP (Cat. # 30304): One vial – 50 µl at 100 mM, use 5 µL of GDP for GDP-labeling of 0.5 mL of cell lysate.

7. HRP-Goat Anti-Rabbit IgG (Cat. #29002): 50 µL (0.4 mg/mL) in PBS, pH 7.4, contained 50% glycerol.

1. Stimulated and non-stimulated cell lysates

2. Protease inhibitors

3. 4 °C tube rocker or shaker

4. 0.5 M EDTA at pH 8.0

5. 1.0 M MgCl2

6. 2X reducing SDS-PAGE sample buffer

7. Electrophoresis and immunoblotting systems

8. Immunoblotting wash buffer such as TBST (10 mM Tris-HCl, pH 7.4, 0.15 M NaCl, 0.05%  Tween-20)

9. Immunoblotting blocking buffer (TBST containing 5% Non-fat Dry Milk or 3% BSA)

10. ECL Detection Reagents

The following figure demonstrates example results seen with the Arl1 Activation Assay Kit. For reference only.

1. Culture cells (one 10-cm plate, ~107 cells) to approximately 80-90% confluence. Stimulate the cells with activator or inhibitor as desired.

2. Aspirate the culture media and wash twice with ice-cold PBS.

3. Completely remove the final PBS wash and add ice-cold 1X Assay/Lysis Buffer (See Reagent Preparation) to the cells (0.5-1 mL per 10 cm tissue culture plate).

4. Place the culture plates on ice for 10-20 minutes.

5. Detach the cells from the plates by scraping with a cell scraper.

6. Transfer the lysates to appropriate size tubes and place on ice.

7. If nuclear lysis occurs, the cell lysates may become viscous and difficult to pipette. If this occurs, lysates can be passed through a 27½-gauge syringe needle 3-4 times to shear the genomic DNA.

8. Clear the lysates by centrifuging at 12,000 x g and 4°C for 10 minutes.

9. Collect the supernatant and store the sample (~1-2 mg of total protein) on ice for immediate use, or snap freeze and store at -70°C for future use.

1. Culture cells and stimulate with activator or inhibitor as desired.

2. Perform a cell count and then pellet the cells through centrifugation.

3. Aspirate the culture media and wash twice with ice-cold PBS.

4. Completely remove the final PBS wash and add ice-cold 1X Assay/Lysis Buffer (See Reagent Preparation) to the cell pellet (0.5-1 mL per 107 cells).

5. Lyse the cells by repeated pipetting.

6. Transfer the lysates to appropriate size tubes and place them on ice.

7. If nuclear lysis occurs, the cell lysates may become viscous and difficult to pipette. If this occurs, lysates can be passed through a 27½-gauge syringe needle 3-4 times to shear the genomic DNA.

8. Clear the lysates by centrifuging at 12,000 x g and 4°C for 10 minutes.

9. Collect the supernatant and store sample on ice for immediate use, or snap freeze and store at -70°C for future use.

1. Aliquot 0.5 mL of cell extract (or 1 µg of purified Ar13 protein) into two microcentrifuge tubes.

2. To each tube, add 20 µL of 0.5 M EDTA (final concentration of 20 mM).

3. Positive control: add 5 µL of 100 X GTPγS (Cat. # 30302) to the 1st tube

4. Negative control: add 5 µL of 100 X GDP (Cat. # 30304) to the 2nd tube.

5. Incubate both tubes at 30°C for 30 minutes with agitation.

6. Stop loading by placing the tubes on ice and adding 32.5 µL of 1 M MgCl2 (final concentration of 60 mM).

1. Aliquot 0.5-1 mL of cell lysates (about 1 mg of total cellular protein) to a microcentrifuge tube.

2. Adjust the volume to 1 mL with 1X Assay/Lysis Buffer (See Reagent Preparation).

3. Add 1 µL anti-Ar13-GTP antibody (Cat. # 26924).

4. Prepare the protein A/G Agarose bead slurry (Cat. # 30301) by resuspending through vertexing or titrating.

5. Quickly add 20 µL of resuspended bead slurry to above tube.

6. Incubate the tube at 4°C for 1 hour with gentle agitation.

7. Pellet the beads through centrifugation at 5,000 x g for 1 min.

8. Aspirate and discard the supernatant (making sure not to disturb or remove the bead pellet.

9. Wash the beads 3 times with 0.5 mL of 1X Assay/Lysis Buffer, centrifuging and aspirating each time.

10. After the third wash, pellet the beads through centrifugation and carefully remove all the supernatant.

11. Resuspend the bead pellet in 20 µL of 2X reducing SDS- PAGE sample buffer.

12. Boil the sample for 5 minutes.

13. Centrifuge it at 5,000 x g for 10 seconds.

1. Load 15 µL/well of pull-down supernatant to a polyacrylamide gel (17%). It is recommended to include a pre-stained MW standard (as an indicator of a successful transfer in step 3 below).

2. Perform SDS-PAGE following the manufacturer’s instructions.

3. Transfer the gel proteins to a PVDF or nitrocellulose membrane following the manufacturer’s instructions.

4. Following electroblotting, immerse the PVDF membrane in 100% Methanol for 15 seconds, and then allow it to dry at room temperature for 5 minutes.

5. Block the membrane with 5% non-fat dry milk or 3% BSA in TBST for 1 he at room temperature with constant agitation.

6. Wash the blotted membrane three times with TBST, 5 minutes each time.

7. Incubate the membrane with anti-Ar13 Mouse Monoclonal Antibody (Cat. # 26056), which has been freshly diluted 1: 50~500 (depending on the amount of Ar13 proteins in your sample) in 5% non-fat dry milk or 3% BSA in TBST, for 1-2 her at room temperature with constant agitation or at 4°C overnight.

8. Wash the blotted membrane three times with TBST, 5 minutes each time.

9. Incubate the membrane with a secondary antibody (Cat. # 29002), which has been freshly diluted 1: 1000 in 5% non-fat dry milk or 3% BSA in TBST, for 1 he at room temperature with constant agitation.

10. Wash the blotted membrane three times with TBST, 5 minutes each time.

11. Use the detection method of your choice such as ECL.