Targeting distinct tautomerase sites of D‐DT and MIF with a single molecule for inhibition of neutrophil lung recruitment

We report a new inflammatory activity for extracellular D‐dopachrome tautomerase (D‐DT), the recruitment of neutrophils to the lung on D‐DT intratracheal installation of C57BL/6J mice with an EC 50 of 5.6 μg. We also find that D‐DT and macrophage migration inhibitory factor (MIF) have additive effects in neutrophil recruitment. Although the tautomerase site of D‐DT and its homologue MIF are biophysically very different, 4‐iodo‐6‐phenylpyrimidine (4‐IPP) forms a co‐valent bond with Pro‐1 of both proteins, resulting in a 6‐phenylpyrimidine (6‐PP) adduct. Recruitment of neutrophils to the lung for the 6‐PP adducts of D‐DT and MIF are reduced by ~50% relative to the apo proteins, demonstrating that an unmodified Pro‐1 is important for this activity, but there is no cooperativity in inhibition of the proteins together. The differences in the binding mode of the 6‐PP adduct for D‐DT was determined by crystallographic studies at 1.13 Å resolution and compared to the structure of the MIF‐6‐PP complex. There are major differences in the location of the 6‐PP adduct to the D‐DT and MIF active sites that provide insight into the lack of cooperativity by 4‐IPP and into tuning the properties of the covalent inhibitors of D‐DT and MIF that are necessary for the development of therapeutic small molecules against neutrophil damage from lung infections such as Pseudomonas aeruginosa in cystic fibrosis and immunocompromised patients.—Rajasekaran, D., Zierow, S., Syed, M., Bucala, R., Bhandari, V., Lolis, E. J., Targeting distinct tautomerase sites of D‐DT and MIF with a single molecule for inhibition of neutrophil lung recruitment. FASEB J. 28, 4961–4971 (2014). www.fasebj.org