a, Circular dichroism spectrum of dualENH at room temperature. Solid line: before thermal denaturation; dashed line: after thermal denaturation. The overlapping of the two curves indicates that dualENH folds reversibly. b, Thermal denaturation curve measured at 222 nm. Circles: experimental data; line: curve fit with two-state transition model. The melting temperature of dualENH was determined to be 59 °C.