MBX2329 and MBX2546 bind to the conserved conformational epitope in the HA stem region. (A and B) Detection of binding of MBX2329 (A) and MBX2546 (B) to recombinant H5 HA by WaterLOGSY NMR. Red arrows represent the aromatic peaks of MBX2329, while green arrows represent the aromatic peaks of MBX2546. For this set of experiments, the conditions were 50 μM MBX2329 or MBX2546 with or without 0.2 μM HA in 20 mM PBS (pH 7.2) at 25°C, using a 900-MHz spectrometer with a mixing time of 2 s. (C and D) Competition WaterLOGSY of MBX2329 (C) and MBX2546 (D) binding to H5 HA in the absence (top spectrum) and in the presence (bottom spectrum) of MAb C179. For this set of experiments, the conditions were 20 μM MBX2329 or 10 μM MBX2546 with or without 0.2 μM HA and with or without 0.4 μM C179 in 50 mM PBS (pH 7.3) at 25°C, using a 900-MHz spectrometer with a mixing time of 2 s.