Aggregation-independent modulation of proteoglycan binding by neutralization of C-terminal acidic residues in the chemokine macrophage inflammatory protein 1 alpha

Members of the chemokine family of proteins mediate their biological effect s through interaction with a family of seven-transmembrane G-protein-couple d receptors. This interaction is complicated by the biochemical properties of chemokines, such as their ability to form self aggregates and their abil ity to bind to proteoglycans. With some chemokines there is a clear interre lationship between these interactions; the chemokine platelet factor 4 bind s preferentially to proteoglycans in its aggregated form. Little is known a bout the role of aggregation in the proteoglycan binding of other chemokine s. Here we demonstrate that the aggregation status of the chemokine macroph age inflammatory protein 1 alpha (MIP-1 alpha) has no detectable effect on its affinity for proteoglycans. Furthermore, we demonstrate that the altera tion of acidic amino acid residues in MIP-1 alpha influences the affinity o f its interactions with heparin as these residues are progressively neutral ized, leading to an enhanced binding affinity for heparin. Thus, with MIP-1 alpha, aggregation is not a determinant of proteoglycan binding; however, overall charge does seem to have a major role in the interaction. These res ults therefore add to our understanding of the nature of the interaction be tween MIP-1 alpha and proteoglycans and suggests that the basic amino acids might not be the sole regulators of proteoglycan binding.