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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Chemistry

Year Degree Awarded

2017

Month Degree Awarded

February

First Advisor

Michael J. Maroney

Second Advisor

Michael J. Knapp

Third Advisor

Scott Garman

Fourth Advisor

Craig T. Martin

Subject Categories

Biochemistry | Inorganic Chemistry

Abstract

Nickel is a rarely used but biologically important metal that is utilized in all three domains of life. In nickel utilizing organisms there is a corresponding trafficking system specifically designed to capture nickel, deliver, and export excess nickel to prevent toxic effects. It is critical to understand the mechanisms by which organisms achieve metal selectivity to duplicate or disrupt this process for the benefit of human health and to further understanding of regulation mechanisms in biology.

RcnR is a Ni(II) and Co(II) responsive transcriptional regulator in E. coli. The research reported in this dissertation focuses on the relationship between structure and function in two hypothesized metal ligand residues, Glu34 and Glu63. The results of these studies indicate that Glu34 is a Co(II) ligand and Glu63 is both a Ni(II) and Co(II) ligand. It is clear from the results of these studies that there is little correlation between metal structure and function in RcnR, and that studies of metal site structure or function alone cannot be used to determine metal response or residue importance. It is clear from analysis of this family of transcriptional regulators that although homologous, they have divergent mechanisms.

Reactive oxygen species (ROS) are a natural byproduct of aerobic metabolism and inflammation, and can be generated through environmental factors such as radiation damage, pollution, and smoking. ROS such as superoxide can cause damage to DNA, lipids, and proteins if left unchecked. Superoxide dismutases are a family of enzymes that catalyze the disproportionation of superoxide to prevent its harmful effects. One of the goals of this dissertation is to investigate how NiSOD exerts control over the redox state of the nickel centers.

NiSOD is a hexamer that cannot be fully oxidized and thus remains 50% Ni(II)/50% Ni(III). One possible reason this occurs is by crosstalk of the nickel centers through a hydrogen bonding network involving His53. Disruption of this crosstalk was attempted by mutation of His53 to alanine. While the experimental evidence indicates the mutation did not disrupt the crosstalk, it is apparent that the entire ~ 40 Å hydrogen bonding network is important for modulating the catalytic mechanism.

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