Author ORCID Identifier
Date of Award
9-2025
Document Type
Thesis (Ph.D.)
Department or Program
Chemistry
First Advisor
Ekaterina Pletneva
Abstract
Heme proteins are crucial for many biological processes including respiration, transport, and catalysis. As electron carriers containing redox active metal centers, their electron transfer (ET) properties are tuned by the protein environment, wherein the reduction potential can be influenced by factors such as heme solvent accessibility, charge, the presence of neighboring redox centers, as well as the identity of the axial ligand. The axial ligand in heme proteins is especially crucial for tuning the electronic properties of the metal center, as it affects the driving force of the reaction. However, the redox properties of heme proteins are further modulated by other facets of the protein structure, such as 2° sphere interactions, protein dynamics, and the presence of neighboring heme groups. Herein, the impact of the axial ligation on conformational and redox properties of monoheme and multiheme cytochrome proteins is examined. In the first study, hydrogen bonds formed by a moiety on the heme periphery were discovered to play a role in stabilizing Met80 ligation to the heme iron in yeast iso-1 cytochrome c. This moiety, heme propionate 6 (HP6), makes particularly critical connections to two low stability substructures in the protein through hydrogen bonding interactions with residues Thr49 and Thr78. Perturbations to this network through the creation of Thr-to-Val mutations affect the stabilities of the Met80- ligated form of the ferric and ferrous protein by comparable amounts, but leads to redox-dependent ligation changes. In the second study, the conformational properties of the yeast iso-1 cytochrome c variant with Thr-to-Val mutations are discovered to be distinct, as groups of hydrophobic residues cluster in the absence of peripheral HP6 contacts to create a channel to the heme. This variant shares similarities with a hydrocarbon-bound structure of cytochrome c, and the implications of this structure in the conformational change of cytochrome c from an electron carrier to a peroxidase are discussed. In the third study, Lys as an axial ligand in yeast iso-1 cytochrome c is revealed to introduce protein dynamics that affect the intramolecular electron transfer kinetics of this protein, shedding light on the properties of this residue as an axial ligand in a number of heme proteins and enzymes. In the final study, the axial ligation of a diheme cytochrome c4 protein from the pathogenic bacteria Neisseria gonorrhoeae is altered to isolate the redox properties of individual heme groups, and facets of the protein structure are discovered to affect the redox properties of the heme domains.
Original Citation
Reik, M. E., Rickett, T. C., Hoke, K. R., Pletneva, E. V. Inorg. Chem. 2025, 64, 24, 11966–11980.
Zhong, F., Reik, M. E., Ragusa, M. J., Pletneva, E. V. J. Inorg. Biochem. 2024, 253, 112496.
Recommended Citation
Reik, Morgan Elisabeth, "Role of Axial Ligation in the Conformational and Redox Properties of Cytochromes" (2025). Dartmouth College Ph.D Dissertations. 429.
https://digitalcommons.dartmouth.edu/dissertations/429
