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

Abstract

The integrin Mac-1 (M{beta}2, 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 MI-domain. However, the binding mechanism of most ligands is not clear. We have determined the interaction of MI-domain with the cytokine pleiotrophin (PTN), a cationic protein known to bind MI-domain and induce Mac-1-mediated cell adhesion and migration. Our data show that PTNs N-terminal domain binds a unique site near the N- and C-termini of the MI-domain using a metal-independent mechanism. However, stronger interaction is achieved when an acidic amino acid in a zwitterionic motif in PTNs C-terminal domain chelates the divalent cation in the metal ion-dependent adhesion site of the active MI-domain. These results indicate that MI-domain can bind ligands using multiple mechanisms, and suggest that active MI-domain prefers acidic amino acids in zwitterionic motifs. HIGHLIGHTSO_LIMI-domains interaction with the cytokine pleiotrophin (PTN) was investigated with solution NMR. C_LIO_LIMI-domain binds PTN using multiple mechanisms. C_LIO_LIPTNs N-terminal domain binds both active and inactive MI-domains using a unique site near MI-domains termini. C_LIO_LIPTNs C-terminal domain binds only active MI-domain through a metal-dependent interaction. C_LI