Aspects of CC Chemokine Structure

Like their CXC counterparts, CC chemokines share a common protein fold, known as a Greek key motif, in which three antiparallel jS-pleated sheets are overlaid by a C-terminal a-helix (Fig. 2A). Following the first pair of cysteine residues is a ten-residue loop known as the N-loop, and then a succession of three jS-strands and a C-terminal a-helix. The three jS-strands are positioned antiparallel to each other and form a )S-pleated sheet that is overlaid at an angle of approximately 75° by the C-terminal a-helix. As might be expected, the existence of four conserved amino-terminal cysteine residues within CC chemokines has structural implications. Using their 

FIGURE 2 Panel A shows the secondary structural Greek Key motif of CC chemokines, as typified by CCL2. Three antiparallel p-pleated sheets overlay a C-terminal, a-helical domain. Panel B shows the elongated CCL2 dimer, which is facilitated by interactions of the chemokine N-termini. The CCL2 monomers making up the dimer are depicted in blue and red. 

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