Figure 4.

The homology models of the hOR o2d2 are constructed by using the program MODELER and BIOPOLYMER in INSIGHT-II (Accelrys). (Left) A model of the nonmetalated apoprotein; the predicted hOR transmembrane helix is aligned to the transmembrane helix of bovine rhodopsin (PDB ID code 1F88). (Right) Proposed structure after binding a metal ion (e.g., Cu²⁺ or Zn²⁺); the alignment shifts to reflect the speculated 4–5 loop insertion and ejection of the fourth helix. (Inset) Predicted coordination geometry to the metal ion from the glutamate, histidine, and cysteine residues of the consensus sequence HXXC[DE] in the 4–5 loop.