Photochemical Sciences Ph.D. Dissertations

Investigations of protein structure-function relationships

Date of Award

2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

Jill Zeilstra-Ryalls (Advisor)

Second Advisor

Jong Kwan Lee (Other)

Third Advisor

H. Peter Lu (Committee Member)

Fourth Advisor

R. Marshall Wilson (Committee Member)

Abstract

This dissertation consists of two parts that together broadly aim to understand the relationship between the structure and function of protein. Part I is a study of the Fe-S cluster assembly system U-type scaffold protein, SufU, from the Gram positive bacterium Bacillus subtilis. The conformational changes of the protein, upon interaction with two different metals, Zn2+ and Fe3+, were investigated. The results indicate that purified SufU that had been stripped of its bound Zn2+ undergoes conformational changes upon reconstitution with Zn2+ ions, but there is no evidence of such changes upon the addition of Fe3+ ions. Thus, B. subtilis SufU discriminates between Zn2+ and Fe3+, and preferentially binds Zn2+ ions. Similar results have been reported for two other U-type proteins, namely, Escherichia coli IscU and Streptococcus mutans SufU, which suggests that these properties are widespread among U-type proteins. Part II is an investigation of the role of the post-translation acetylation modification of the Rhodobacter sphaeroides Puc1B protein. Together with PucA, PucB comprises the structural component of one of two light harvesting (LH) complexes that deliver photons to the photosynthesis reaction center. Rba. sphaeroides encodes two such sets of PucB and A proteins; Puc1B and Puc1A, and Puc2B and Puc2A. While the amino acid sequence of Puc1B differs by only 3 residues from Puc2B, mass spectrometry data indicate that only the former is acetylated. The findings presented here indicate that acetylation is important for efficient assembly of LH2. The specificity required to acetylate Puc1B, and not Puc2B, evokes an enzyme-catalyzed process, which raises the possibility that Puc1B acetylation is a regulated event, and the rate of acetylation of Puc1B might then govern the rate of LH2 assembly.

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