Characterization of the binding site on heparan sulfate for macrophage inflammatory protein 1

The CC chemokine macrophage inflammatory protein 1 (MIP1 ) is a key regulator of the proliferation and differentiation of hematopoietic progenitor cells. The activity of MIP1 appears to be modulated by its binding to heparan sulfate (HS) proteoglycans, ubiquitous components of the mammalian cell surface and extracellular matrix. In this study we show that HS has highest affinity for the dimeric form of MIP1 . The predominantly dimeric BB10010 MIP1 interacts with an 8.3-kDa sequence in the HS polysaccharide chain, which it protects from degradation by heparinase enzymes. The major structural motif of this HS fragment appears to consist of 2 sulfate-rich S-domains separated by a short central N-acetylated region. The optimum lengths of these Sdomains seem to be 12 to 14 saccharides. We propose that this binding fragment may wrap around the MIP1 dimer in a horseshoe shape, facilitating the interaction of the S-domains with the heparinbinding domains on each monomer. Molecular modeling suggests that these S-domains are likely to interact with basic residues Arg 17, Arg 45, and Arg 47 and possibly with Lys 44 on MIP1 and that the interconnecting N-acetylated region is of sufficient length to allow the 2 Sdomains to bind to these sites on opposite faces of the dimer. Elucidation of the structure of the HS-binding site for MIP1 may enable us to devise ways of enhancing its myeloprotective or peripheral blood stem cell mobilization properties, which can be used to improve cancer chemotherapy treatments. (Blood. 2002;100: 1543-1550)