A glance at the metal binding ability of fungal ZIP transporters: Zn(II) and Cu(II) interaction with the Zrt2 protein

Zrt2 is a zinc transporter of the ZIP family, located in the cell membrane and proved to be the major zinc importer in Candida albicans under acidic conditions.[1] Since many transition metal ions, and in particular zinc, are crucial for the survival and proliferation of C. albicans cells in the human organism, understanding the mechanisms of metal acquisition and regulation is necessary to design new effective antifungal drugs.[2] The predicted three-dimensional structure of Zrt2 protein showed the presence of an extra-membrane, disordered loop containing at least three possible metal binding sequences which have not been characterized before: GPHTHSHFGD, PSHFAHAQEHQDP and DDEEEDLE. Therefore, the corresponding model peptides protected at their termini have been thermodynamically and spectroscopically investigated to elucidate their Zn(II) and Cu(II) coordination properties and to identify the most effective metal binding site. Potentiometric titrations, mass spectrometry and different spectroscopic techniques (UV-Vis absorption, circular dichroism, electron paramagnetic resonance) have been employed to thoroughly study the metal interaction with the selected protein fragments. To better understand the biological role of the Zrt2 protein, we compared its ability to bind metal ions with that of potential competitor systems, including the zinc-transporter Zrt1 and the human zinc-binding peptide calcitermin, which proved to be active against C. albicans.[3] Financial support of the Polish National Science Centre (UMO-2020/37/N/ST4/03165) and of the COST Action CA18202, NECTAR – Network for Equilibria and Chemical Thermodynamics Advanced Research is gratefully acknowledged.