A structurally preserved allosteric site in the MIF superfamily affects enzymatic activity and CD74 activation in D‐dopachrome tautomerase

Abstract

The human macrophage migration inhibitory factor (MIF) superfamily consists of MIF and D‐dopachrome tautomerase (also called MIF‐2). Both MIF proteins have critical innate and adaptive immunomodulatory functions in regulating differentiation, expression of pro‐inflammatory cytokines, and activation and recruitment of immune cells. They are broadly and constitutively expressed, but elevated levels of MIF family proteins are upregulated in various inflammatory diseases such as asthma, acute respiratory distress syndrome (ARDS) and arthritis, and antibody neutralization of MIF decreased inflammatory symptoms in murine models. While their potential as drug targets has led to the creation of a few commercial inhibitors of MIF, the efficacy of targeting MIF proteins as a therapeutic is currently obstructed by a lack of molecular level detail about their structures and dynamics and how those properties impact disease‐state activity.Previously, we reported a dynamic relay connecting the MIF catalytic site to an allosteric site at its solvent channel. The MIF homolog DDT (MIF‐2) has low sequence identity with MIF (35%) though they overlap in multiple functions, including activation of the CD74 receptor, and share a nearly identical tertiary structure. This prompted the question of whether this dynamic regulatory network is conserved within the superfamily. We identify a comparable allosteric network in MIF‐2, connecting the catalytic site to CD74‐activating residues, showing with solution nuclear magnetic resonance (NMR) spectroscopy that dynamic communication is preserved in MIF‐2 despite differences in primary sequence. Disruption of the allosteric relay by mutagenesis also attenuates MIF‐2 enzymatic activity in vitro and biological CD74 signaling in vivo, highlighting amino acids in this pathway as trigger residues for potential functional control of the protein.