Unrevealing the antimicrobial properties of calcitermin and its peptide derivatives

Thanks to the broad spectrum of activity and scarce attitude to induce antimicrobial resistance, antimicrobial peptides (AMPs) represent a rational chance to overcome the current drug-resistance crisis. Among several uncharacterized molecules that contribute to the overall antimicrobial activity of human nasal fluid, a 15-residue antimicrobial peptide named calcitermin (VAIALKAAHYHTHKE) has been identified [1]. Calcitermin contains a metal-binding domain with three alternated histidine residues (His9, His11 and His13) and the free terminal amino and carboxyl groups. Based on our preliminary studies, it exhibits an improved microbicidal activity when Zn2+ or Cu2+ ions are present in the culture medium. Additionally, calcitermin His-to-Ala mutants – where each histidine residue is replaced with one alanine – have different metal coordination modes, resulting in significant changes of the antimicrobial properties [2]. These promising results prompted us to focus on calcitermin derivatives where the peptide structure is modified in order to confer higher proteolytic stability. The first task of this work consists of a careful evaluation of the enzymatic stability of native calcitermin in human plasma. Afterwards, C- and/or N- terminal modifications have been introduced to possibly obtain calcitermin derivatives resistant to proteases [3]. Changes in the peptide backbone, and in particular the N-terminus protection, can affect the calcitermin metal-binding behaviour and therefore further investigations on the metal interaction with the synthesized protected peptides have been performed, in order to connect the antimicrobial activity of calcitermin with the complex-formation ability. The characterization of metal complexes has been performed by means of several techniques, including potentiometry, high-resolution mass spectrometry, NMR, UV-Vis, circular dichroism and EPR. The obtained results will allow us to propose and design new therapeutic antimicrobial strategies based on calcitermin derivatives and their metal complexes. 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. [1] M. Cole, Y.-H. Kim, S. Tahk, T. Hong, P. Weis, A. J. Waring, and T. Ganz, FEBS Lett. 504 (2001) 5-10. [2] D. Bellotti, M. Toniolo, D. Dudek, A. Mikołajczyk, R. Guerrini, A. Matera-Witkiewicz, M. Remelli, and M. Rowińska-Żyrek, Dalton Trans. 48 (2019) 13740-52. [3] X. Lai, J. Tang, and M. E. H. ElSayed, Expert Opin. Drug Discov. (2021) 1-16.