Protein recognition of macrocycles: binding of anti-HIV metallocyclams to lysozyme.
The macrocyclic antiviral drug xylyl-bicyclam blocks entry of HIV into cells by targeting the CXCR4 coreceptor, a seven-helix transmembrane G-protein-coupled receptor. Its affinity for CXCR4 is enhanced by binding to Cu2+, Ni2+, or Zn2+. Metallocyclams have a rich configurational chemistry and proteins may bind selectively to specific metallocyclam configurations. Our studies of lysozyme reveal structural details of protein-metallocyclam interactions that are important for receptor recognition. Solution NMR studies show that Cu-cyclam interacts with specific tryptophan residues of lysozyme (Trp-62, Trp-63, and Trp-123). Two major binding sites for both Cu-cyclam and Cu2-xylyl-bicyclam were detected by x-ray crystallography. In the first site, Cu2+ in one cyclam ring of Cu2-xylyl-bicyclam adopts a trans configuration and is coordinated to a carboxylate oxygen of Asp-101, whereas for Cu-cyclam two ring NH groups form H bonds to the carboxylate oxygens of Asp-101, stabilizing an unusual cis (folded) cyclam configuration. For both complexes in this site, a cyclam ring is sandwiched between the indole side chains of two tryptophan residues (Trp-62 and Trp-63). In the second site, a trans cyclam ring is stacked on Trp-123 and H bonded to the backbone carbonyl of Gly-117. We show that there is a pocket in a model of the human CXCR4 coreceptor in which trans and cis configurations of metallobicyclam can bind by direct metal coordination to carboxylate side chains, cyclam-NH...carboxylate H bonding, together with hydrophobic interactions with tryptophan residues. These studies provide a structural basis for the design of macrocycles that bind stereospecifically to G-coupled and other protein receptors.
Hunter
Tina M
TM
School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, United Kingdom.
McNae
Iain W
IW
Liang
Xiangyang
X
Bella
Juraj
J
Parsons
Simon
S
Walkinshaw
Malcolm D
MD
Sadler
Peter J
PJ
D000818:Animals; D019380:Anti-HIV Agents / Q000737:chemistry* / Q000378:metabolism*; D001596:Benzylamines; D001665:Binding Sites; D002645:Chickens; D018360:Crystallography, X-Ray; D000080027:Cyclams; D006571:Heterocyclic Compounds / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D047029:Lactams, Macrocyclic / Q000737:chemistry* / Q000378:metabolism*; D008670:Metals / Q000378:metabolism*; D008958:Models, Molecular; D009113:Muramidase / Q000378:metabolism*; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding; D019718:Receptors, CXCR4 / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism
D019380:Anti-HIV Agents; D001596:Benzylamines; D000080027:Cyclams; D006571:Heterocyclic Compounds; D047029:Lactams, Macrocyclic; D008670:Metals; D019718:Receptors, CXCR4; D009113:Muramidase; C088327:plerixafor