A 25 mM sodium phosphate buffered solution of protein (1.0 mg/mL, pH 7.0) was added to 50 μg/mL purified LplA in 25 mM sodium phosphate buffer, 10 v/v% of 3.2 mM aqueous MgSO4, 20 equivalent of 20 mM Sodium azido-octanoate in DMSO, and 10 v/v% of 2.5 mM aqueous ATP. This reaction mixture (final mAb conc. was 0.8 mg/mL) was incubated at 30 °C. After 64 h incubation, the residual enzyme was quenched with 2 μL of aqueous EDTA-2Na solution. The purified product was buffer-exchanged with 20 mM PBS buffer (pH 7.4) by Centripure P50 according to a previous protocol. All reaction solution of azide-modified protein was then combined with DBCO-Cy3 using click chemistry agent. Following experimental protocol was described in previous work .