Histidine-Rich C‑Terminal Tail of Mycobacterial GroEL1 and Its Copper ComplexThe Impact of Point Mutations

The mycobacterial histidine-rich GroEL1 protein differs significantly compared to the well-known methionine/glycine-rich GroEL chaperonin. It was predicted that mycobacterial GroEL1 can play a significant role in the metal homeostasis of Mycobacteria but not, as its analogue, in protein folding. In this paper, we present the properties of the GroEL1 His-rich C-terminus as a ligand for Cu­(II) ions. We studied the stoichiometry, stability, and spectroscopic features of copper complexes of the eight model peptides: L1Ac-DHDHHHGHAH, L2Ac-DKPAKAEDHDHHHGHAH, and six mutants of L2 in the pH range of 2–11. We revealed the impact of adjacent residues to the His-rich fragment on the complex stability: the presence of Lys and Asp residues significantly increases the stability of the system. The impact of His mutations was also examined: surprisingly, the exchange of each single His to the Gln residue did not disrupt the ability of the ligand to provide three binding sites for Cu­(II) ions. Despite the most possible preference of the Cu­(II) ion for the His9–His13 residues (Ac-DKPAKAEDHDHHH-) of the model peptide, especially the His11 residue, the study shows that there is not only one possible binding mode for Cu­(II). The significance of this phenomenon is very important for the GroEL1 functionif the single mutation occurs naturally, the protein would be still able to interact with the metal ion.