Structural features of the coreceptor. a. Overall view of the coreceptor. The CXCR4 polypeptide is shown in green, lysozyme (fused to assist crystallization) is shown in orange, the inhibitor peptide in magenta. The amino acids in contact with the inhibitor peptide are shown in cyan and in surface representation. The approximate position of the membrane is shown as gray rectangles (not in crystal structure). b. Cross-section and close-up of the pocket. Colors as in panel a. c. PepSite hotspots for amino acid binding on the coreceptor surface. Hotspots for binding of individual amino acids in the pocket of CXCR4 (alanine: salmon; cysteine: cyan; glutamate and aspartate: red; phenylalanine, tryptophan, tyrosine: gray; glycine: orange; histidine: light gray; isoleucine, leucine, valine: yellow; arginine, lysine: blue; methionine: light orange; asparagine, glutamine: green; proline: magenta; serine, threonine: purple). CXCR4 is rendered transparent for clarity.