Molecular design to mimic the copper(II) transport site of human albumin. The crystal and molecular structure of copper(II) – glycylglycyl-L-histidine-N-methyl amide monoaquo complex
Glycylglycyl-L-histidine-N-methyl amide is a Cu-binding tripeptide designed and synthesized to mimic the Cu transport site of human albumin. Reddish-purple crystals of the Cu tripeptide amide complex (Cu-GGHa), grown at physiological pH, are triclinic, with cell dimensions a = 9.990, b = 9.986, c = 7.682 A, .alpha. = 107.40, .beta.-91.72, .gamma. = 96.49, space group Pl, Z = 2 units of Cu GGHa and 2 H2O molecules per cell. The structure was solved by interpretation of a Cu-phased Fourier map containing a great deal of false symmetry, after multiple attempts with direct phasing methods failed. Refinement proceeded to R = 0.036. The conformations of the 2 Cu-GGHa units are virtually identical. Each Cu is tetradentate chelated by the amino terminal N, the next 2 peptide N and a histidyl N of a single tripeptide molecule in a mildly distorted square planar arrangement. The Cu...N distances range between 1.90-2.05 A, with N...Cu...N angles of 165 and 176. An O atom provides a 5th position weaker interaction in each case, with Cu...0 distances of 2.61 and 2.88 A.