Zinc and Its Critical Role in Retinitis pigmentosa: Insights from DFT/SMD Calculations

Metal cations are required for the proper function of a great amount of biological processes, as they are indispensable cofactors participating in up to 40% of the active sites of the proteins. In the case of some diseases, however, metal cations could exhibit a dual function. As an example, the role of the zinc cation in the development of Retinitis pigmentosa could be given. Experimental works indicate the loss of thermostability of the rhodopsin protein, subjected to the combination of-typical for the disease-mutations and increased quantity of Zn2+. Two structural networks in the intradiscal domain surrounding His100 and His195 are supposed to be susceptible to pathophysiological changes in trace metal concentrations. From a thermodynamic point of view, it is of particular interest to decipher the foundations of the observed outcome, as well as to closely characterize the intimate interactions between the native cation and the building amino acid residues of the studied centers. Therefore, the powerful, but fundamentally limited, tools of computational chemistry were applied on simplified models of rhodopsin metal centers in order to shed light on the following aspects: (1) what is the preferred geometry of the Zn2+-containing complexes with the amino acid ligands from the binding pockets; (2) what is the role of the mutations for the interactions between Zn2+ and the examined centers; (3) could other divalent cations such as Ca2+ and Cu2+ substitute for the native zinc; (4) how does the dielectric constant of the environment affect the processes? The obtained results illuminate some aspects of the zinc coordination to amino acid residues and zinc biochemistry related to the presumed pathogenesis of Retinitis pigmentosa.