Thermodynamics and Structural Effects of Metal Ions Binding to the Antimicrobial Peptide Calcitermin

Author

Matthew Alexander Barnett, University of San FranciscoFollow

Date of Graduation

Fall 12-31-2025

Document Type

Thesis

Degree Name

Master of Science in Chemistry

College/School

College of Arts and Sciences

Department/Program

Chemistry

First Advisor

Michael J. Stevenson

Second Advisor

Janet G. Yang

Third Advisor

Natalia Powers-Riggs

Abstract

Antibiotic-resistant infections have become the defining global public health threat of the 21^st century. The widespread use and overuse of currently available antibiotics have accelerated antimicrobial resistance, and the slow pace of traditional antibiotic drug discovery over the past few decades has led to a shortage of novel antimicrobial agents to treat multidrug-resistant pathogens. Alternatives to traditional antibiotics are a promising source of next-generation agents to treat infectious diseases, and one such source is antimicrobial peptides (AMPs), which often exhibit broad-spectrum activity against pathogens and low levels of resistance. Calcitermin (VAIALKAAHYHTHKE), a 15-mer AMP isolated from human airways. Calcitermin exhibits antimicrobial activity against bacteria and fungi under acidic conditions (pH 5.4), and its activity against some microbes, particularly C. albicans, is greatly potentiated in the presence of Cu²⁺ and Zn²⁺. However, the mechanism of action of calcitermin remains elusive, as does the mechanism of potentiation of these metal ions. Previous work has characterized the binding of these metal ions, but not the complete thermodynamics of binding, an aspect increasingly recognized in drug discovery and development. Here, isothermal titration calorimetry is used to quantify the binding thermodynamics between these metal ions and calcitermin. Cu²⁺ binds to calcitermin with nanomolar affinity, while Zn²⁺ binds with micromolar affinity. Both binding interactions are entropically driven, with the binding of Cu²⁺ having a greater enthalpic penalty but overall greater favorability. Additionally, ¹H and ¹H-¹H nuclear magnetic resonance spectroscopy were used to investigate metal-binding sites; it was found that both metals bind to all three histidine residues in the HxHxH motif, and the data suggest that Cu²⁺ coordinates the N-terminus while Zn²⁺ coordinates the E15 or C-terminal carboxylate. Taken together, these thermodynamic and structural insights may guide future understanding of metal-AMP interactions and drug development as an alternative to traditional antibiotics.

Recommended Citation

Barnett, Matthew Alexander, "Thermodynamics and Structural Effects of Metal Ions Binding to the Antimicrobial Peptide Calcitermin" (2025). Master's Theses. 1628.
https://repository.usfca.edu/thes/1628