Degree

Doctor of Philosophy (PhD)

Department

Department of Biological Sciences

Document Type

Dissertation

Abstract

Iron-sulfur clusters as key cofactors are involved in multiple cellular processes, such as central metabolism and respiration, gene regulation and DNA repair. In Escherichia coli, iron-sulfur clusters are assembled by a group of dedicated proteins. While the sulfide in iron-sulfur clusters is derived from L-cysteine via cysteine desulfurase IscS, the iron source still remains unknown. It has been proposed that IscA and its paralog SufA may act as iron chaperones for iron-sulfur cluster biogenesis. The first part of this work focuses on the interplay between cysteine desulfurase IscS and iron chaperons IscA/SufA. The results show that deletion of IscA/SufA generates a novel red-colored cysteine desulfurase IscS. The red-colored IscS can also be produced in wild-type E. coli cells by depleting intracellular iron using a membrane-permeable iron chelator 2,2’-dipyridyl. The red-colored IscS has its unique redox property and spectroscopic features. When wild-type IscS is incubated with excess L-alanine and sulfide, red-colored IscS is also formed in vitro, indicating that the red IscS may contain a conjugated pyridoxal phosphate quinonoid intermediate. This study suggests an important physiological interplay between IscA and IscS in iron-sulfur cluster biogenesis. The second part of this work is to explore the relation between iron homeostasis and iron-sulfur cluster biogenesis. The results demonstrate that deletion of IscA/SufA disrupts iron homeostasis in E. coli cells and produces an unprecedented iron-bound ferric uptake regulator Fur. Furthermore, the expression of gene fur in the iscA/sufA mutant cells is down-regulated, which leads to high expression of the ferric transporter FhuA and FecA. Introduction of exogenous Fur or deletion of the ferric transporter operon fecABCDE in the iscA/sufA mutant cells partially restores the cell growth defect. The results suggest that overloading of intracellular iron may contribute to the growth inhibition of the E. coli cells with deficiency of iron-sulfur cluster biogenesis and that iron homeostasis is closely associated with iron-sulfur cluster biogenesis.

Date

10-16-2018

Committee Chair

Ding, Huangen

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