Specific labeling of Igκ-LPETG–derived serum immunoglobulins and purified B cells using SrtA. (A) Serum from OB1 HC^+/- Igκ-LPETG^+/+ mice was labeled using GGG-biotin and StrA. Immunoglobulins were then immunoprecipitated with protein G and analyzed by immunoblot using streptavidin-HRP. (B) Purified primary B cells from Igκ-LPETG mice were labeled using GGG-biotin and StrA. The B cells were then lysed and analyzed by immunoblot using streptavidin-HRP. The doublet is attributable to the use of the Vκ1-135 and the Vκ 2-137 segments (see text). (C) Purified primary B cells isolated from Igκ-LPETG^+/+ mice were labeled as described in (B) for different durations. (D) Primary B cells from Igκ-LPETG^+/+ mice were labeled as described in (B) using GGG-Alexa-647 or GGG-Cy5 as nucleophiles. The cells were then surface stained and analyzed by flow cytometry. The cells were gated on AAD^-CD19⁺Igκ⁺ cells. All blots and FACS plots shown are representative of at least 3 independent experiments.