Peculiar Features in the Crystal Structure of the Adduct Formed between <i>cis</i>-PtI₂(NH₃)₂ and Hen Egg White Lysozyme

Abstract

The reactivity of <i>cis</i>-diamminediiodidoplatinum­(II), <i>cis</i>-PtI₂(NH₃)₂, the iodo analogue of cisplatin, with hen egg white lysozyme (HEWL) was investigated by electrospray ionization mass spectrometry and X-ray crystallography. Interestingly, the study compound forms a stable 1:1 protein adduct for which the crystal structure was solved at 1.99 Å resolution. In this adduct, the Pt^II center, upon release of one ammonia ligand, selectively coordinates to the imidazole of His15. Both iodide ligands remain bound to platinum, with this being a highly peculiar and unexpected feature. Notably, two equivalent modes of Pt^II binding are possible that differ only in the location of I atoms with respect to ND1 of His15. The structure of the adduct was compared with that of HEWL–cisplatin, previously described; differences are stressed and their important mechanistic implications discussed