No abstract

Fe 4 S 4 ] iron-sulfur clusters are typically anchored to the protein scaffold via four cysteine residues, but in a number of proteins one of the Cys is replaced with another ligand. The biological role of such a replacement is unknown although essential to maintain catalytic activity. Here, we explore the geometries and electronic structures of 3:1 site differentiated model compounds [Fe 4 S 4 ][S(CH 3 )] 3 (L) using quantum chemical methods. The unique ligands L were chosen to represent biologically relevant molecules: methanethiol (represents cysteine), acetic acid (asparagine), 4-methylimidazole (histidine), and water/ hydroxyl anion. Each ligand was considered as deprotonated anion or protonated neutral molecule. We found the replacements do not influence structure of the cluster significantly. On [a]