Conjugation of Cy7APC to Immunoglobulins:
Brief Protocol

See the detailed protocol for information.

I. Preparation of APC

Dialyze or exchange the APC into "C Reaction Buffer". Concentration before derivatization is typically 5-10 mg/ml. If the APC is stored as a SAS precipitate, it must be extensively dialyzed prior to use: 2 changes of 1 liter per ml APC of PBS before dialyzing against 1 liter per ml of "C Reaction Buffer".

Use 1.7 mg of APC per mg of IgG to be modified; this includes an extra 10% for loss during buffer exchanges.

To check the APC purity, measure the absorbance at 280, 620 and 655 nm. (1 mg/ml of APC has an OD at 655nm of 5.9). A 655/620 ratio >1.4 indicates adequate removal of contaminating phycocyanin; a 655/280 ratio > 4 indicates adequate removal of all other proteins.

II. Cy7 conjugation of APC

Dissolve the appropriate amount of bis-Cy7 in DMSO at 10 mg/ml. Add 91.1 nmol of Cy7 per mg of APC.

Incubate and rotate for 60 minutes. Exchange into "Dialysis Buffer" over gel filtration.

Take an absorbance spectrum of the product to ensure proper derivatization.

III. SMCC conjugation of Cy7APC

Prepare a 10 mg/ml stock solution of SMCC in dry DMSO immediately prior to use.

Add 11 µl of SMCC per mg of Cy7APC while vortexing. Wrap the reaction tube in aluminum foil and rotate at room temperature for 60 minutes.

Pass the derivatized Cy7APC over a gel filtration column pre-equilibrated with "Exchange Buffer".

IV. Reduction of IgG

Prepare a fresh solution of 1 M DTT (15.4 mg/100 µl) in distilled water.

IgG solutions should be at 4 mg/ml or higher for best results. Make each IgG solution 20 mM in DTT: add 20 µl of DTT stock per ml of IgG solution while mixing. Let stand at room temp for 30 minutes without additional mixing (to minimize reoxidation of cysteines to cystines).

Pass the reduced IgG over a filtration column pre-equilibrated with "Exchange Buffer". Collect 0.25 ml fractions off the column; determine the protein concentrations and pool the fractions with the majority of the IgG. Carry out the conjugation as soon as possible after this step.

V. Covalent conjugation

Add 1.5 mg of SMCC-Cy7APC per mg of IgG. Wrap the reaction tube in aluminum foil and rotate for 60 minutes at room temp.

Prepare a fresh solution of 10 mg NEM in 1.0 ml dry DMSO.

Add 34 µg (3.4 µl) per mg of IgG. Wrap and rotate for 20 minutes at room temperature.

The product can be either dialyzed or exchanged over a column into an appropriate buffer (e.g. "Storage Buffer").


"C Reaction Buffer": 500 mM carbonate, pH 9.0. For 1 liter: 17g Na2CO3, 28g NaHCO3

"Dialysis Buffer": 50 mM Sodium phosphate, 1 mM EDTA, pH 7.0. For 1 liter: 13.41g Sodium phosphate dibasic (7*H2O); 0.37 g EDTA

"Exchange Buffer": 50 mM MES, 2 mM EDTA, pH. 6.0. For 1 liter: 9.76 g MES, 0.74 gm EDTA

"Storage Buffer": 10 mM Tris, 150 mM NaCl, 0.1% (w/v) NaN3 (azide), pH 8.2. For 1 liter: 1.42g TRIZMA 8.0, 8.77g NaCl, 5 mL 20% NaN3