αMI-domain of Integrin Mac-1 Binds the Cytokine Pleiotrophin Using Multiple Mechanisms

Abstract

SUMMARYThe integrin Mac-1 (αMβ2, CD11b/CD18, CR3) is an important adhesion receptor expressed on macrophages and neutrophils. Mac-1 is also the most promiscuous member of the integrin family that binds a diverse set of ligands through its αMI-domain. However, the binding mechanism of most ligands is not clear. We have determined the interaction of αMI-domain with the cytokine pleiotrophin (PTN), a cationic protein known to bind αMI-domain and induce Mac-1-mediated cell adhesion and migration. Our data show that PTN’s N-terminal domain binds a unique site near the N- and C-termini of the αMI-domain using a metal-independent mechanism. However, stronger interaction is achieved when an acidic amino acid in a zwitterionic motif in PTN’s C-terminal domain chelates the divalent cation in the metal ion-dependent adhesion site of the active αMI-domain. These results indicate that αMI-domain can bind ligands using multiple mechanisms, and suggest that active αMI-domain prefers acidic amino acids in zwitterionic motifs.HIGHLIGHTSαMI-domain’s interaction with the cytokine pleiotrophin (PTN) was investigated with solution NMR.αMI-domain binds PTN using multiple mechanisms.PTN’s N-terminal domain binds both active and inactive αMI-domains using a unique site near αMI-domain’s termini.PTN’s C-terminal domain binds only active αMI-domain through a metal-dependent interaction.