Fig. 5 ABL1 FRET biosensor corroborates functional resistance

Figure 5 introduces and validates a novel BCR::ABL1 FRET biosensor designed to measure the structural dynamics of the kinase in response to asciminib. After establishing that the biosensor's fluorophore insertions do not distort the native pharmacological profile or cellular drug sensitivity, dose-response analyses demonstrated that asciminib binding drives the wild-type protein into a "closed," high-FRET inactive state. In contrast, known resistance mutations, as well as the epistatic double mutation of V73A and Y253H, exhibit reduced sensitivity to asciminib-induced clamping and effectively remain in an active, "open" conformation. Ultimately, a strong negative correlation (r = -0.82) was observed between the biosensor's measurement of conformational openness and cellular dose-response sensitivity, revealing that diverse asciminib resistance mutations converge on a shared biophysical failure to undergo the required allosteric conformational shift.