N-terminal domain of eotaxin-3 is important for activation of CC chemokine receptor 3

Eotaxin-3 belongs to the CC chemokine family, and specificallyrecognizes CC chemokine receptor (CCR) 3 that is expressed oneosinophils, basophils and helper T type 2 cells. The three-dimensionalstructure of eotaxin-3 determined by nuclear magnetic resonancehas revealed that the N-terminal nine residues preceding thefirst cysteine comprise an unstructured domain, which is alsoobserved in other chemokine molecules. In order to determinethe function of the N-terminal domain of eotaxin-3, we constructedvarious N-terminal-deletion mutants, and then examined theirbinding and chemotactic activities toward eosinophils in vitro.Competitive binding studies showed that the binding affinityof truncated mutant toward CCR3 was almost the same as thatof wild-type eotaxin-3 even though the N-terminal truncationinvolved the first through to the ninth residues. In contrast,the chemotactic activity gradually decreased with extensionof the N-terminal deletion, and when the deletion extended tothe eighth residue, the activity was not detected at all. Thus,the N-terminal nine residues are not critical for binding butthe N-terminal eight residues are essential for activation ofCCR3. The truncated eotaxin-3 proteins lacking the N-terminaleight or nine residues inhibited the chemotactic activity ofchemokines that recognize CCR3. The truncated mutants can possiblybe used for anti-allergic and anti-HIV-1 therapy.