Reactivity of G309 and S310 HER2 mutants to pertuzumab and trastuzumab. Recombinant G309 and S310 mutant, wild-type HER2 or wild-type HER3 human Fc fusion protein was coated onto the wells of microtiter plates. The plate was blocked and subjected to incubation with (a) recombinant pertuzumab scFv-human Cκ fusion protein, or (b) trastuzumab scFv-human Cκ fusion protein at varying concentrations. Wild-type HER3 human Fc fusion protein was used as a negative control, because it does not bind to either antibody. The amount of bound antibody was determined using HRP-conjugated human Cκ light chain antibody and 3,3′,5,5′-tetramethyl benzidine (TMB) substrate solution.