Phycoerythrin conjugation protocol
David's method modified from references (2) and (3). I used this method to conjugate a mouse IgG2a monoclonal antibody (IB4). It works well.
Reagents
| Ab | Antibody, about 2.5 mg/ml |
| PE | R-Phycoerythrin, purified (Molecular Probes P-801 in 60% ammonium sulfate) |
| PBS | Phosphate buffered saline without Ca2+/Mg2+ |
| MeOH | Methanol |
| DMSO | Dimethyl sulphoxide, anhydrous |
| SPDP | 3-(2-pyridyldithio)propionic acid N-hydroxysuccinimide ester (Sigma) |
| SMCC | Succinimidyl trans-4-(N-maleimidylmethyl)cyclohexane-1-carboxylate (Molecular Probes) |
| DTT | Dithiothreitol |
| NEM | N-ethyl maleimide |
| * | 10 ml Sephadex G-10 columns (2) |
| Separation column | A long Sephacryl S-300 column. I used 117 x 1 cm. You can't really get away with anything smaller. Use a long thin one rather than a short fat one, since the latter did not work for me. Separation of the conjugate from the free reagents is tricky. |
| * | Centricon 30 and Centriprep 30 centrifugal concentrators (Amicon) |
| * | Room temperature is about 22 °C |
Method
1. Preparation of PE0.25 ml of P-801. Spin 10 mins on low in microfuge. Discard supernatant. Resuspend PE in 0.25 ml PBS. Dialyze twice for 30 mins versus 150 ml PBS at room temperature.
Add 16 µl SPDP (1.3 mg/ml in MeOH)
Incubate at room temperature for 2.5 hours
*** You must time steps 3 and 4 to finish at the same time, since the reaction products are unstable ***
Add 20 µl SMCC, 1.7 mg/ml in DMSO.
Incubate for 1 hour.
Incubate for 30 mins at room temperature.
Order of elution is conjugate first (MW ~400,000) then free PE (MW ~240,000) then free Ab (MW ~150,000). Begin collecting 1.0 ml fractions when pink band approaches bottom of column and continue for 10 fractions after it has disappeared.
Add 0.5% sodium azide. Store at 4 °C protected from light. Do not freeze.
Figure 1. Analysis of column eluate fractions from PE conjugation of monoclonal antibody IB4 (murine IgG2a, anti-human CD18). The optical density of each fraction was measured at 280 nm and 565 nm (OD280 and OD565 respectively). An aliquot of each fraction was used to stain human neutrophils which were then analyzed using a FACScan flow cytometer (Becton-Dickinson). Median cellular fluorescence intensity in the FL2 (orange fluorescence) channel is shown.
References
1. Chambers JD, Simon SI, Berger EM, Sklar LA, Arfors K-E. Endocytosis of beta2 integrins by stimulated human neutrophils analyzed by flow cytometry. Journal of Leukocyte Biology 53: 462-469 (1993)
2. Kronick MN, Grossman PD. Immunoassay techniques with fluorescent phycobiliprotein conjugates. Clinical chemistry 29: 1582-1586 (1983)
3. Oi VT, Glazer AN, Stryer L. Fluorescent phycobiliprotein conjugates for analyses of cells and molecules. Journal of Cell Biology 93: 981-986 (1982)
