Structural probing of Zn(II), Cd(II) and Hg(II) binding to human ubiquitin.

A structural investigation performed on adducts of human ubiquitin with group-12 metal ions reveals common preferential anchoring sites, the most populated one being His68; at higher metal ion concentration a second and a third site, close to the N-terminus of the protein, become populated and promote a polymorphic transition from orthorhombic to cubic form; Glu16 and Glu18, involved in the latter metal binding, undergo a remarkable displacement from their position in native ubiquitin; the aggregate stereochemistry appears to be driven by the clustering of deshielded backbone hydrogen-bond patches, and metal ions foster this process.