X-Ray Crystal Structure and Solution Properties of [Au(III)(H-2-Gly-Gly-L-His)]Cl.H2O

Gold(Ill) generated via myeloperoxidase is thought to play an important role in the side-effects of anti-arthritic gold drugs [1, 2]. Au(lll)-modified peptides bound to MHC class II molecules may be involved in delayed hypersensitivity reactions (’gold rashes’) observed in patients undergoing chrysothempy, but little is known about the binding of Au(lll) to peptides. Only one crystal structure of a Au(lll) peptide has previously been described [3]. For our studies, we used glycylglycyI-L-histidine (GGH), a model for the N-terminal copper binding site of serum albumin. The reaction of GGH with NaAuCI4 at low pH (1.5-2) is slow (T1/2 ca. 6 h, 10 mM, 310 K) and involves one intermediate. The structure of the final product [Au(III)(H.2-GlyGly-L-His)]CI.H20 has been determined by X-my crystallography. It is square-planar with Au(lll) coordinated to the terminal NH2, two deprotonated peptide NH’s and His NS. The structure of this complex in solution and its behaviour at pH 7 will be discussed.