Phosphorylation/dephosphorylation is likely the most crucial chemical reaction taking place in all
living organisms. It is the basis for the regulatory control of many diverse biological events
triggered by extracellular effectors. Moreover, it is a ubiquitous element of intracellular signal
transduction pathways that regulates a wide range of processes. While protein phosphorylation has
been extensively characterized in eukaryotes, far less is known about its emerging counterparts
in prokaryotes. This study involved determination of the crystal structures and functional
characterization of two protein kinases, YihE and AceK (also a protein phosphatase), and two
nucleotide pyrophosphatases, YjjX and YhdE. X-ray crystallographic structure determination
combined with bioinformatics analyses, mutageneses and biochemical experiments, both in vitro
and in vivo, were utilized for the functional characterization of each protein. YihE was found to
be a previously unknown kinase component of a new type of bacterial phospho-relay mechanism,
thus adding kinase activity as another response to the Cpx sensing system that functions to
maintain cellular homeostasis. AceK, which possesses both kinase and phosphatase activities,
modifies isocitrate dehydrogenase (ICDH) to regulate the flux of isocitrate into the glyoxylate
cycle. The structures of Acek alone and in complex with its substrate, ICDH, provided us with
information to explain the mechanisms underlying its bifunctionality and its molecular switch.
Through structural comparison and, particularly, functional characterization, we revealed that
YjjX is a novel ITPase/XTPase responsible for the removal of non-canonical nucleotides from
the cell during oxidative stress in Escherichia coli. YhdE, identified as a novel dTTPase, was
observed to retard cell growth and form a filamentous phenotype when overexpressed in the cell,
suggesting that YhdE is involved in the control of cell growth and division by regulating the cell
nucleotide pool for DNA synthesis. In summary, this research has made a substantial
ii
contribution to the investigation of bacterial phosphorylation and dephophorylation systems that
respond to various environmental conditions. / Thesis (Ph.D, Biochemistry) -- Queen's University, 2009-05-29 11:41:41.832
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OKQ.1974/5908 |
| Date | 24 June 2010 |
| Creators | Zheng, JIMIN |
| Contributors | Queen's University (Kingston, Ont.). Theses (Queen's University (Kingston, Ont.)) |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Rights | This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner. |
| Relation | Canadian theses |
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