Figure 4. Improved SrtA variants are efficient at labelling an anti-HER2 antibody.

(A) Four versions of an anti-HER2 antibody were generated with a tag for sortase conjugation on either the N or C-terminus of both heavy and light chains. Corresponding peptide tag sequences are shown in the Methods and Materials section. Each antibody contains identical heavy and light chains, although only one tag is depicted here for simplicity. (B) LC/MS trace showing labelling of the light chain C-terminus tagged antibody (LC-C) with either 60 μM of WT SrtA or 2.5 μM of the 5M/Y187L/E189R SrtA variant using GGGY-Lys(Biotin)-NH₂. (C) LC/MS trace comparing labelling of the heavy chain N-terminus tagged antibody (HC-N) with 0.025 μM of either WT, 5M, or 5M/D124G SrtA using Biotin-C6-LELPETGG-NH₂.