Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves [157]-179).

published_or_final_version / Surgery / Master / Master of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Sphingolipids and ceramides are essential components of cellular membranes and important signalling molecules. Because of a growing appreciation for their diverse biological roles, understanding of the biosynthesis and regulation of sphingolipids has recently become a key goal in drug discovery. Serine palmitoyltransferase (SPT) is a pyridoxal 5′-phosphate (PLP)-dependent enzyme that catalyses the condensation between L-serine and a long-chain acyl thioester such as palmitoyl-CoA (C16-CoA). This first step in sphingolipid biosynthesis is conserved in all organisms studied to date, from microbes to man. The fungal natural product myriocin is a potent inhibitor of SPT; however, the molecular details of inhibition are not fully understood. Myriocin contains a long alkyl chain and a polar head group thus it displays features of both SPT substrates. Therefore, the prevailing hypothesis is that inhibition of SPT occurs because myriocin acts as a mimic of a key transition state of the catalytic mechanism. Through a combination of UV-vis spectroscopy, mass spectrometry, x-ray crystallography and enzyme inhibition assays it has been possible to study the interaction between S. paucimobilis SPT and myriocin. I have shown that myriocin initially forms an inhibitory PLP:myriocin aldimine complex in the active site that displays a Ki of 967 nM. Interestingly, this complex is susceptible to unexpected, slow enzymatic degradation. The mechanism for myriocin breakdown has been elucidated as a retro-aldol type reaction, which results in cleavage of the C2-C3 bond producing a C18 aldehyde. This aldehyde is then capable of covalently modifying the active site lysine265, forming a second (suicide) inhibitory complex and rendering the enzyme catalytically inactive. Substitution of the active site lysine produced SPT K265A, an inactive enzyme that did not catalyse the breakdown of the PLP:myriocin complex. However, the determination of the crystal structure of the SPT K265A:PLP-myriocin complex revealed that the myriocin had undergone decarboxylation. Nevertheless, this SPT:PLP:decarboxymyriocin structure revealed details about myriocin’s mechanism of inhibition for the first time. The novel mechanism of myriocin degradation has implications on the structure activity relationship (SAR) and design of drugs targeted towards SPT, the role of feedback regulation by long chain aldehydes and further expands the range of reactions catalysed by this important enzyme. As well as inhibition studies the structure of bacterial SPT was also examined by preparing an N-terminally truncated S. paucimobilis SPT. This version, shortened by 21 amino acids, was ~5-fold slower than the wild-type enzyme and suggests that the N-terminus may play a role in catalysis. Additional work has been undertaken to study an unusual membrane-bound viral SPT, composed of two naturally fused open reading frames (SPT2-SPT1) with the proposed SPT2 domain at the N-terminus and the SPT1 domain at the C-terminus. To study soluble mimics of this interesting fusion I prepared a bacterial S. paucimobilis SPT fused wild-type and mutant construct and isolated a fused SPT2-SPT1 with what appears to be single PLPbinding site.

With the increasing demand for assisted reproduction, more knowledge and understanding towards health requirements of oocytes and their inner workings are required. With current IVF success rates of approximately 40%, oocyte and embryo culture conditions in vitro can be improved by first understanding the finer details of oocyte function. As such, there is a need to better understand the mechanisms through which oocytes can acquire certain nutrients. This thesis focuses on the amino acid serine, which has been shown to improve outcome in developing embryos and also plays a variety of roles in the body that may carry over to oocyte health as well. Using radiolabeled [3H] serine, we measured uptake of serine as a function of time throughout growth and meiotic maturation in mouse oocytes. Serine transport appeared in oocytes during growth and became absent in mature eggs. With a competition assay using substrates diagnostic for several different amino acid transporter systems and culture with and without sodium in the external medium, I identified Na+-dependent SNAT7 of the System A/N (SLC38) family to be the most likely transporter in oocytes. Quantitative RT-PCR was consistent with this result. Transporter activity is also not activated by progression of meiotic maturation, as indicated by unperturbed transport when dbcAMP was provided to maintain meiotic arrest. However, a biological regulator of arrest, NPPC, resulted in enhanced transport activity in vitro. This may be due to signalling mechanisms of the NPPC pathway affecting regulation of serine uptake, which presents a direction for future research.

Induced and activated as part of the innate immune response, the first line of defence against bacterial or viral infections, Inhibitor of Kappa-B Kinase ε (IKKε) triggers NF-κB and IFNβ signalling. Whilst not expressed at basal levels in healthy cells and tissue, the kinase is overexpressed in roughly 30% of human breast cancer cases, driving oncogenesis through aberrant activation of NF-κB. The impracticality of therapeutic targeting of NF-κB for cancer treatment has led to a requirement for greater understanding of IKKε's oncogenic potential to treat tumours driven by the kinase. Considering that IKKε alters cellular metabolism in dendritic cells, promoting aerobic glycolysis akin to the metabolic phenotype observed in cancer, it was hypothesised that the kinase would play a similar role in breast cancer. Using a Flp-In 293 model of IKKε induction and suppressing IKKε expression in a panel of breast cancer cell lines using siRNA, IKKε-dependent changes in cellular metabolism were characterised using labelled metabolite analysis. IKKε was found to induce serine biosynthesis, an important pathway in breast cancer development that supports glutamine-fuelling of the TCA cycle and contributes to one carbon metabolism to maintain redox balance. Promotion of serine biosynthesis occurred via a dual mechanism. Firstly, PSAT1, the second enzyme of the pathway, was found to be phosphorylated in an IKKε-dependent manner, promoting protein stabilisation. Secondly, an IKKε-dependent transcriptional upregulation of all three serine biosynthesis enzymes, PHGDH, PSAT1 and PSPH, was observed, induced by the inhibition of mitochondrial activity and the subsequent induction of ATF4-mediated mitochondria-to-nucleus retrograde signalling. These data demonstrate a previously uncharacterised mechanism of metabolic regulation by IKKε and highlight new potential therapeutic targets for the treatment of IKKε-driven breast cancer in the form of the enzymes of the serine biosynthesis pathway.

Regulatory protein phosphorylation is a well conserved mechanism of signal transduction in all biological systems. In bacteria, signal transduction by phosphorylation is thought to occur primarily on His and Asp residues. However, phosphoproteomic surveys in phylogenetically diverse bacteria over the past decade have identified numerous proteins that are phosphorylated on serine (Ser) and/or threonine (Thr) residues. Consistently, genes encoding Ser/Thr kinases are present in many bacterial genomes such as E. coli, which encodes at least three Ser/Thr kinases. Since Ser/Thr phosphorylation is a stable modification, a dedicated phosphatase is necessary to allow reversible regulation. Bacterial Ser/Thr phosphatases which have extensive sequence and structural homology to eukaryotic Ser/Thr PP2C-type phosphatases are referred to as eukaryotic-like Ser/Thr phosphatases (eSTPs). eSTPs have been identified in a number of bacteria, but none have been reported in E. coli. The work presented in this thesis was aimed at identifying and biochemically characterizing a eukaryotic-like Ser/Thr phosphatase and its partner Ser/Thr kinase in E.coli. Chapter 3 describes the identification of a novel PP2C-like Ser/Thr phosphatase PphC encoded by an E. coli ORF, yegK, and characterization of its biochemical properties including kinetics, substrate specificity and sensitivity to known phosphatase inhibitors. I investigated differences in the activity of this protein in closely related E. coli strains. Finally, I demonstrated that this eSTP acts to dephosphorylate a novel Ser/Thr kinase which is encoded in the same operon suggesting that they most likely function as a pair in regulating Ser/Thr phosphorylation. Chapter 4 describes the biochemical characterization of a Ser/Thr kinase YegI in E. coli. I show that YegI is an active kinase with significant structural homology to eukaryotic Ser/Thr kinases. The YegI kinase domain is tethered to a cytoplasmic C-terminal domain containing two non-specific DNA binding Helix-hairpin helix motifs. I have identified enolase and elongation factor-Tu (EF-Tu) as potential physiological substrates of YegI and have demonstrated that phosphorylation of EF-Tu by YegI inhibits protein translation in vitro.

SR蛋白在前體信使核糖核酸(pre-mRNA)的組成性剪接和選擇性剪接中扮演者重要的角色，在這個過程中它需要被SR蛋白激酶(SRPK) 燐酸化才能正常行使功能。經典的SR蛋白是由N端一到二個RNA識別基序(RRM) 以及C端一串精氨酸－絲氨酸(RS) 二肽所構成。SR蛋白的燐酸化調控它的亞細胞定位以及生理功能。此外，SR 蛋白激酶1(SRPK1) 和SR蛋白原型ASF/SF2的復合物結構顯示底物的結合需要第二個非標準的RRM結構域以及在N端可以被燐酸化的RS結構域，但是，第一個標準的RRM結構域對於SR 蛋白激酶1的結合卻是可以或缺的。 / 在這裡，我們展示了SR蛋白激酶2(SRPK2) 結合並且燐酸化SRp20的RS結構域，SRp20是另外一個只包含一個RNA識別基序(RRM) 的SR蛋白。與ASF/SF2相似的是，SRp20中的標準RNA識別基序對於SRPK2的結合並不是必要的。與此同時，我們發現錨定槽對於底物的識別作用在SRPK2中也是保守的，因為，錨定槽中四個關鍵氨基酸的突變會削弱它對SRp20的結合。 / 此外，現在認為SRPK2的功能已經不限於對前體信使核糖核酸(pre-mRNA) 的剪接調控。最近發現，SRPK2也可以燐酸化Tau蛋白並且介導阿爾茨海默疾病中的認知性缺陷。組成性的激活是SR蛋白激酶中的一個固有特性，然而人們對於它的調控機制還不是很清楚。因此, 為了更好的瞭解SRPK2，我們采用酵母雙雜交的方法並且最終發現一個新的SRPK2相互作用蛋白: ZNF187。 / ZNF187是一個可以結合血清反應元件(SRE) 的轉綠因子。我們的研究發現，它可以正向調控SRE的轉錄激活。然而，SRPK2在EGF的刺激下卻起着抑制的效果，其中EGF的刺激會促使SRPK2進入細胞核。進一步證實，通過RNAi干擾的方法敲掉SRPK2可以增加ZNF187誘導的SRE活性。在共轉染實驗中，SRPK2可以把ZNF187誘導的SRE活性逆轉到本底水平。對於可以和EGF刺激的SRPK2有着相似細胞定位的缺失或者突變研究發現，它們都可以產生相一致的抑制現象。於此相反，對於和SRPK2有着不同細胞定位的突變，它卻不能產生抑制效果。因此，我們認為在EGF的刺激下，SRPK2進入細胞核並且負向的調控ZNF187激活的SRE。令人驚訝的是，如果細胞在FBS的刺激下，SRPK2卻上調SRE活性，並且它可以協同增加ZNF187對於SRE的誘導。這些結果表明SRPK2對於ZNF187誘導的SRE轉綠調控是刺激物依賴的。 / SR proteins are critical players in regulating both constitutive and alternative pre-mRNA splicing, during which the phosphorylation by SR Protein Kinases (SRPKs) is required. Classical SR proteins contain one or two RNA Recognition Motifs (RRM) in their N terminus and a stretch of Arginine-Serine (RS) dipeptides in C terminus. Phosphorylation status of SR proteins regulates their subcellular localization as well as physiological function. In addition, complex structure of SRPK1 with ASF/SF2, a prototype of SR protein, shows that substrate binding requires non-canonicalRRM2 domain and RS domain, which can be extensivelyphosphorylated. However, the canonical RRM1 domain is dispensable for such interaction. / Here we show that SRPK2 binds and phosphorylates SRp20, a classical single RRM domain-containing SR protein, at its RS domain. Similarly with ASF/SF2, the canonical RRM domain of SRp20 is dispensable for interacting with SRPK2. Meanwhile, we also find that a docking groove that iscritical for substrate binding in SRPK1 is also conserved in SRPK2, since mutations on four key residues in docking groove impair its binding affinity with SRp20. / In addition, SRPK2 is now known to function more then regulating mRNA splicing, such as cell proliferation and cell apoptosis. Recently, SRPK2 is also shown to be a kinase phosphorylating Tau and mediate the cognitive defects in Alzheimer’s disease (AD). Besides, an intrinsic character of SRPKs lies in that they are constitutively active, but the regulation mechanism is not well understood. Therefore, in order to obtain a better recognition about SRPK2, we applied yeast two-hybrid assay and eventually anew interaction partner called ZNF187 was identified. / ZNF187 is a transcriptional factor that binds with Serum Response Element (SRE). Our studies showed that it isa positive regulator of SRE activity. However, SRPK2 showed inhibiting effect on SRE activation with the treatment of EGF, which could induce its nucleus entry, when co-transfected, it reversed the stimulating effect on SRE by ZNF187 to basal level. Furthermore, knockdown of SRPK2 by RNAi would enhance ZNF187-stimuated SRE activation. Studies on truncation and mutations that have the similar effect with EGF-induced subcellular localization of SRPK2 also generated the same inhibiting phenomenon. In contrast, mutant that has distinct localization with SRPK2 wild type failed to exert suppression. Therefore, we conclude that with the treatment of EGF, SRPK2 moves into nucleus and negatively regulates ZNF187-stimulated transactivation of SRE. Surprisingly, when cells were treated with FBS, SRPK2 showed stimulation on SRE activity and it synergized ZNF187-stimulated effect on SRE, indicating that transcriptional regulation of SRPK2 on ZNF187-stimulated SRE activity is stimuli-dependent. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Shang, Yong. / Thesis (Ph.D.) Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 113-137). / Abstracts also in Chinese.

Li, Man Wah. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 109-119). / Abstracts in English and Chinese. / Thesis Committee --- p.I / Statement --- p.II / Abstract --- p.III / 摘要 --- p.V / Acknowledgements --- p.VI / Abbreviations --- p.VIII / Abbreviations of Chemicals --- p.X / List of Tables --- p.XI / List of Figures --- p.XII / Table of Contents --- p.XIII / Chapter Chapter 1 --- Literature Review --- p.1 / Chapter 1.1 --- General amino acid control in yeast --- p.1 / Chapter 1.2 --- Mammalian eIF2α kinases --- p.7 / Chapter 1.2.1 --- Heme-regulated inhibitor kinase (EIF2AK1/HRI) --- p.7 / Chapter 1.2.2 --- Protein kinase dsRNA-dependent (EIF2AK2/PKR) --- p.8 / Chapter 1.2.3 --- PKR-like ER kinase (EIF2AK3/PERK) --- p.9 / Chapter 1.2.4 --- General control non-repressible 2 (EIF2AK4/GCN2) --- p.10 / Chapter 1.2.5 --- Activating transcription factor 4 (ATF4) --- p.11 / Chapter 1.3 --- Plant General Amino Acid Control --- p.12 / Chapter 1.3.1 --- Studies of the homolog of GCN2 in Arabidopsis thaliana --- p.12 / Chapter 1.3.2 --- Studies of the homolog of other eIF2a kinase in plant --- p.14 / Chapter 1.3.3 --- Studies of the homolog of other GAAC components --- p.14 / Chapter 1.4 --- Previous works in our lab --- p.15 / Chapter 1.5 --- Hypothesis and Objectives --- p.17 / Chapter Chapter 2 --- Materials and Methods / Chapter 2.1 --- Materials --- p.18 / Chapter 2.1.1 --- "Bacterial cultures, plant materials and vectors" --- p.18 / Chapter 2.1.2 --- Primers --- p.21 / Chapter 2.1.3 --- Commercial kits --- p.25 / Chapter 2.1.4 --- "Buffer, solution, gel and medium" --- p.25 / Chapter 2.1.5 --- "Chemicals, reagents and consumables" --- p.25 / Chapter 2.1.6 --- Enzymes --- p.25 / Chapter 2.1.7 --- Antibodies --- p.25 / Chapter 2.1.8 --- Equipments and facilities --- p.25 / Chapter 2.2 --- Methods --- p.26 / Chapter 2.2.1 --- Growth conditions of Arabidopsis thaliana --- p.26 / Chapter 2.2.1.1 --- Surface sterilize of Arabidopsis thaliana seed --- p.26 / Chapter 2.2.1.2 --- Growing of Arabidopsis thaliana --- p.26 / Chapter 2.2.1.3 --- Treatment of Arabidopsis seedling --- p.26 / Chapter 2.2.2 --- Basic molecular techniques --- p.27 / Chapter 2.2.2.1 --- Liquid culture of Escherichia coli --- p.27 / Chapter 2.2.2.2 --- Preparation of plasmid DNA --- p.27 / Chapter 2.2.2.3 --- Restriction digestion --- p.27 / Chapter 2.2.2.4 --- DNA purification --- p.28 / Chapter 2.2.2.5 --- DNA gel electrophoresis --- p.28 / Chapter 2.2.2.6 --- DNA ligation --- p.29 / Chapter 2.2.2.7 --- CaCl2 mediated E. coli transformation --- p.29 / Chapter 2.2.2.8 --- Preparation of DNA fragment for cloning --- p.29 / Chapter 2.2.2.9 --- PCR reaction for screening positive E. coli transformants --- p.30 / Chapter 2.2.2.10 --- DNA sequencing --- p.30 / Chapter 2.2.2.11 --- RNA extraction from plant tissue with tRNA --- p.31 / Chapter 2.2.2.12 --- Extraction of RNA without tRNA --- p.31 / Chapter 2.2.2.13 --- cDNA synthesis --- p.32 / Chapter 2.2.2.14 --- SDS-Polyacrylamide Gel Electrophoresis (SDS-PAGE) --- p.33 / Chapter 2.2.2.15 --- Western blotting --- p.33 / Chapter 2.2.3 --- Sub-cloning of AtGCN2 --- p.34 / Chapter 2.2.3.1 --- Sub-cloning full length AtGCN2 into pMAL-c2 --- p.36 / Chapter 2.2.3.2 --- Sub-cloning of the N-terminal sequence of AtGCN2 into pMAL-c2 --- p.38 / Chapter 2.2.3.3 --- Sub-cloning of the C-terminal sequence of AtGCN2 into pMAL-c2 --- p.38 / Chapter 2.2.4 --- Cloning of the eIF2α candidates for the in vitro assay --- p.41 / Chapter 2.2.4.1 --- Cloning of At2g40290 (putative eIF2α candidate) --- p.41 / Chapter 2.2.4.2 --- Cloning of At5g05470 (putative eIF2α candidate) into pBlueScript KS II + --- p.43 / Chapter 2.2.4.3 --- Sub-cloning of At5g05470 into pGEX-4T-1 --- p.43 / Chapter 2.2.4 --- Expression and purification of fusion proteins --- p.45 / Chapter 2.2.5 --- Expression of fusion proteins in E. coli --- p.45 / Chapter 2.2.5.2 --- Extraction of E. coli soluble proteins --- p.45 / Chapter 2.2.5.3 --- Purification of GST tagged fusion protein --- p.46 / Chapter 2.2.5.4 --- Purification of MBP tagged fusion protein --- p.46 / Chapter 2.2.5.5 --- Concentration of purified fusion proteins --- p.46 / Chapter 2.2.5.6 --- MS/MS verification of purified fusion proteins --- p.47 / Chapter 2.2.6 --- Gel mobility shift assay --- p.47 / Chapter 2.2.6.1 --- Synthesis of short biotinylated RNA --- p.47 / Chapter 2.2.6.2 --- Ligation of short biotinylated RNA with tRNA --- p.48 / Chapter 2.2.6.3 --- Gel mobility shift assay --- p.48 / Chapter 2.2.6.4 --- Blotting of the sample on to nitrocellulose membrane --- p.48 / Chapter 2.2.6.5 --- Detection of the tRNA on the membrane --- p.49 / Chapter 2.2.6.6 --- Detection of the MBP fusion proteins on the membrane --- p.49 / Chapter 2.2.7 --- In vitro kinase assay of AtGCN2 --- p.49 / Chapter 2.2.8 --- In vitro translation inhibition assay --- p.50 / Chapter 2.2.8.1 --- In vitro transcription of HA mRNA --- p.50 / Chapter 2.2.8.2 --- In vitro translation --- p.51 / Chapter 2.2.8.3 --- Detection of the protein dot blot --- p.51 / Chapter 2.2.9 --- Gene expression analysis by real time PCR --- p.52 / Chapter 2.2.10 --- Total seed nitrogen analysis --- p.53 / Chapter Chapter 3 --- Results / Chapter 3.1 --- Blast search results suggested that AtGCN2 may be the sole eIF2α kinase in Arabidopsis thaliana --- p.54 / Chapter 3.2 --- Existence of two eIF2α candidates in Arabidopsis thaliana genome --- p.59 / Chapter 3.3 --- Fusion proteins were successfully expressed and purified --- p.63 / Chapter 3.4 --- C-terminal of AtGCN2 has a higher affinity toward tRNA than rRNA --- p.67 / Chapter 3.5 --- Both eIF2α candidates can be phosphorylated by full length AtGCN2 in vitro --- p.70 / Chapter 3.6 --- AtGCN2 can inhibit translation in vitro --- p.72 / Chapter 3.7 --- Overexpression of AtGCN2 did not affect expression of selected genes --- p.74 / Chapter 3.8 --- Overexpression of AtGCN2 did not affect seed nitrogen content and C:N ratio under normal growth conditions --- p.83 / Chapter Chapter 4 --- Discussion --- p.85 / Chapter 4.1 --- Existing evidence supported that AtGCN2 is the sole eIF2α kinase in Arabidopsis thaliana --- p.85 / Chapter 4.2 --- Kinase activities of AtGCN2 and its two substrates in Arabidopsis --- p.86 / Chapter 4.3 --- C-terminal binds tRNA in the gel mobility shift assay --- p.88 / Chapter 4.4 --- Overexpression of AtGCN2 did not affect gene expression of the transgenic lines under nitrogen starvation and azerserine treatment --- p.90 / Chapter 4.5 --- Overexpression of AtGCN2 did not alter the seed nitrogen content --- p.91 / Chapter 4.6 --- Existence of GCN4 and ATF4 in plant --- p.92 / Chapter 4.7 --- Alternative model without GCN4 and ATF4 homolog --- p.93 / Chapter 4.8 --- Possible application of the in vitro kinase assay --- p.94 / Chapter 4.9 --- Possible application of the in vitro translation inhibition analysis platform in future study --- p.95 / Chapter Chapter 5 --- Conclusion and Future Prospective --- p.97 / Appendices / Appendix I Commercial kits used in this project --- p.98 / "Appendix II Buffer, solution, gel and medium" --- p.99 / "Appendix III Chemicals, reagents and consumables" --- p.102 / Appendix IV Enzymes --- p.103 / Appendix V Antibodies --- p.104 / Appendix VI Equipments and facilities --- p.105 / Appendix VII Supplementary Data --- p.106 / Appendix VIII Amplification efficiency of real time primers --- p.108 / References --- p.109

L'objectif était d'effectuer la première synthèse total de Cyclothéonamide C (CTC), un pentapeptide macrocyclique, inhibiteur puissant des sérine protéases. Il a plusieurs motifs structuraux uniques, comprenant un vinylogue de déshydrotyrosine (V-deltaTyr) et une alpha-Cétohomoarginine (K-Arg). Le plus grand défi résidait à créer le résidu K-Arg ou un précurseur approprié alpha-Hydroxyhomoarginine (H-Arg) dans des intermédiaires peptidiques avancés. On propose trois stratégies différentes pour y parvenir : "Passerini-Acyl Migration" (PAM), "Masked Acyl Cyanide" (MAC) et "alpha-Keto-Acyl Cyanide" (KAC) . Une préparation préalable de peptides électrophiles et nucléophiles (aldéhydes et alpha-cétocyanophosphoranes ; amines et isonitiles) est nécessaire pour l'exécution des différentes stratégies. Les trois stratégies sont alors développées pour fournir des pentapeptides linéaires transformés ensuite en macrocycliques. Les étapes de déprotection et d'oxydation finissent formellement la synthèse de CTC