Overcharging of the Zinc Ion in the Structure of the Zinc-Finger Protein Is Needed for DNA Binding Stability.

Zinc-finger structure, in which a Zn2+ ion binds to four cysteines or histidines in a tetrahedral structure, is a very common motif of nucleic acid-binding proteins. The corresponding interaction model is present in 3% of the genes in the human genome. As a result, the zinc finger has been extremely useful in various therapeutic and research capacities and in biotechnology. In a stable configuration of the zinc finger, the cysteine amino acids are deprotonated and become negatively charged. Thus, the Zn2+ ion is overscreened by four cysteine charges (overcharged). Whether this overcharged configuration is also stable when such a negatively charged zinc finger binds to a negatively charged DNA molecule is unknown. We investigated how the deprotonated state of cysteine influences its structure, dynamics, and function in binding to DNA molecules by using an all-atom molecular dynamics simulation up to the microsecond range of an androgen receptor protein dimer. Our results showed that the deprotonated state of cysteine residues is essential for the mechanical stabilization of the functional, folded conformation. This state stabilizes not only the protein structure but also the protein-DNA binding complex. The differences in the structural and energetic properties of the two sequence-identical monomers are also investigated and show the strong influence of DNA on the structure of the zinc-finger protein dimer upon complexation. Our result can potentially lead to a better molecular understanding of one of the most common classes of zinc fingers.