Chemokines are relatively small cytokines which regulate cell movement, also known as chemotaxis. To mediate downstream functions, they bind to chemokine receptors which contain seven transmembrane domains. These receptors are typically promiscuous and bind to multiple chemokine ligands.
Chemokines contain several (typically four) cysteine residues in conserved positions within the protein (marked C in the image below) which provide tertiary structure through disulfide bonds. The spacing of the intervening amino acids (denoted X below) between the first two cysteine residues determine the type of chemokine.