Mammalian metallothioneins ([Formula: see text]) show a clustered arrangement of the metal ions and a nonregular protein structure. The solution structures of Cd(3)-thiolate cluster containing beta-domain of mouse beta-MT-1 and rat beta-MT-2 show high structural similarities, but widely differing structure dynamics. Molecular dynamics simulations revealed a substantially increased number of NH-Sgamma hydrogen bonds in beta-MT-2, features likely responsible for the increased stability of the Cd(3)-thiolate cluster and the enfolding protein domain. Alterations in the NH-Sgamma hydrogen-bonding network may provide a rationale for the differences in dynamic properties encountered in the beta-domains of MT-1, -2, and -3 isoforms, believed to be essential for their different biological function.