Fig. 3: TKI sensitivity of exon 19 variants is determined by K_{M, ATP}.

a Michaelis-Menten plots for the indicated EGFR kinase domains in the presence of 20 μM peptide substrate (n = 3 separate protein preparations, with three independent experiments for each) with the TKD concentrations listed in Methods. Normalized mean initial velocity data were plotted against ATP concentration (error bars represent SD across replicates) and fit to the Michaelis–Menten equation to obtain values for K_{M, ATP}. b The mean value of K_{M, ATP} obtained by fitting data from individual ATP concentration series is plotted (± SD). The bar for wild type kinase is grey, profile 1 variants in blue, profile 2 variants in red, L858R variants in olive, and the unactivated ΔL747-E749 variant in black. Data represent three separate protein protein preparations, with three independent experiments for each. c Overlay of the 2.96 Å crystal structure of the ∆L747-E749 exon 19 variant (PDB ID: 7TVD – see Table 2), shown in black, with the wild type EGFR TKD from PDB entry 1M14⁴⁰, shown in grey. Both TKDs are in the active conformation, but the deletion in the β3/αC loop displaces αC slightly towards the ATP-binding site in ∆L747-E749 (see green arrow). The residues deleted in ∆L747-E749 (L747, R748, and E749) are shown in orange in the wild type structure. d Close-up of the β3/αC region in the overlay of ΔL747-E749 on the wild type EGFR TKD, showing that β3 is slightly truncated at its C-terminus in ΔL747-E749 and αC loses a helical turn at its N-terminus—allowing the shortened β3/αC loop to link the two elements. Source data are provided as a Source data file.