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

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Abstract
Members of the chemokine family of proteins mediate their biological effects through interaction with a family of seven-transmembrane G-protein-coupled receptors. This interaction is complicated by the biochemical properties of chemokines, such as their ability to form self aggregates and their ability to bind to proteoglycans. With some chemokines there is a clear interrelationship between these interactions; the chemokine platelet factor 4 binds preferentially to proteoglycans in its aggregated form. Little is known about the role of aggregation in the proteoglycan binding of other chemokines. Here we demonstrate that the aggregation status of the chemokine macrophage inflammatory protein 1α (MIP-1α) has no detectable effect on its affinity for proteoglycans. Furthermore, we demonstrate that the alteration of acidic amino acid residues in MIP-1α influences the affinity of its interactions with heparin as these residues are progressively neutralized, leading to an enhanced binding affinity for heparin. Thus, with MIP-1α, aggregation is not a determinant of proteoglycan binding; however, overall charge does seem to have a major role in the interaction. These results therefore add to our understanding of the nature of the interaction between MIP-1α and proteoglycans and suggests that the basic amino acids might not be the sole regulators of proteoglycan binding.