Systematic Model Peptide Studies: A Crucial Step To Understand the Coordination Chemistry of Mn(II) and Fe(II) in Proteins

Pathogenic bacteria and all other species require Mn(II) and Fe(II) ions for proper growth. Microbes use a variety of assimilation pathways to obtain the necessary metal ions, and their metal homeostasis mechanisms are still not fully uncovered. The knowledge of the poorly discovered complexation chemistry of Mn(II) and Fe(II) ions could help us to understand the basis of those processes better. We have designed six model peptides (L1 - Ac-HHHHHH-NH2, L2 - Ac-HHHHHHHHH-NH₂, L3 - Ac-HAHAHAHAH-NH₂, L4 - Ac-HHAAAAAAAAAHHHH-NH₂, L5 - Ac-HDHDHDHDH-NH₂, and L6 - Ac-HEHEHEHEH-NH₂) inspired by Mn(II) and Fe(II) binding motifs that are prevalent in nature, in order to clarify their coordination preferences. Spectrometric, spectroscopic, and potentiometric techniques were used to determine the thermodynamic and structural properties of the studied systems. All of the investigated ligands possess efficient Mn(II), Fe(II), and Zn(II) binding sites. Complex stability and metal affinity are significantly influenced by the length of the peptide sequences, as well as the location and quantity of coordinating amino acid residues like His, Asp, and Glu.