Structural and Functional Studies of Biotin-Dependent Carboxylases

A persisting question in biology concerns the exceptional diversity of metabolic enzymes and how they respond to their ligands and dynamic environments with remarkable precision. In humans, the family of biotin-dependent carboxylases holds important roles in intermediary metabolism. Recent years have witnessed significant progress toward understanding these enzymes' roles in homeostatic regulation. However, due to a lack of structural information, their catalytic mechanisms, as well as the macromolecular consequences of their genetic mutations, are still not well understood. This dissertation describes the characterization of two biotin-dependent carboxylases that catalyze essential metabolic transformations in humans and bacteria, using X-ray crystallography to elucidate their structures and biochemical assays to verify their activities. We engineer a novel chimeric variant of propionyl-CoA carboxylase (PCC) and produce the first crystal structure of its 750-kDa α6β6 holoenzyme. This structure reveals the architecture of PCC's twelve catalytic domains and allows the mapping of its disease-associated gene mutations to predict their effects on enzyme stability and catalysis. We also identify and describe a new domain that is integral to maintaining inter-subunit contacts within PCC. Following this, we extend our studies to methylcrotonyl-CoA carboxylase (MCC), another 750-kDa α6β6 holoenzyme that differs from PCC primarily in its substrate preference. The crystal structure of MCC assumes a markedly different configuration from PCC despite the high sequence identity between the two. Theorizing that these enzymes may represent unique lineages in the evolution of the biotin-dependent carboxylases, we apply similar approaches to the study of a third biotin-dependent carboxylase. Our efforts have produced the first two holoenzyme structures of CoA-recognizing biotin-dependent carboxylases, and provide valuable insight for understanding the functions of these vital enzymes

A Chronology for the Identification and Disclosure of Adverse Effects of Succinylcholine

Background: New therapies are created to address specific problems and enjoy popularity as they enter widespread clinical use. Broader use can reveal unknown adverse effects and impact the life cycle significantly. Succinylcholine, a depolarizing neuromuscular blocker, was the product of decades of research surrounding the ancient compound, curare. It was introduced into practice in the 1940s by Burroughs Wellcome and Company (BW Co.) and was welcomed due to its rapidly acting muscle relaxation effects. Global clinical use revealed adverse effects, both minor and major, in particular, hyperkalemia and malignant hyperthermia. We investigated when practitioners and the manufacturer became aware of these adverse effects, how information about these side effects were disseminated, and whether the manufacturer met the regulatory requirements of the time, specifically regarding the timely reporting of adverse effects. Sources: Primary literature search using online and archived documents was conducted at the Wood Library-Museum of Anesthesiology, Schaumburg, Illinois. We consulted documents submitted by BW Co. to federal authorities, through the Freedom of Information Act (FOIA), Food and Drug Administration (FDA) reports, promotional advertisements, package inserts, published articles, and textbooks. Results: Initial clinical testing in humans in 1952 found no adverse effects on cardiovascular or respiratory systems. Fasciculations and myalgia were early side effects described in case reports in 1952. Large-scale clinical trials in 1953 found abnormally long recovery times among some patients; the discovery of abnormal pseudocholinesterase enzyme activity was not fully demonstrated until the early 1960s. Bradycardia was first reported in 1957 in children, and in 1959 in adults. In 1960, animal studies reported a transient increase in plasma potassium; further experiments in 1969 clearly demonstrated succinylcholine-induced hyperkalemia in burn patients. Malignant hyperthermia was first described in 1966. Similar cases of elevated temperatures and muscle rigidity were described globally but the underlying mechanism was not elucidated until the 1990s. Standard anesthesia textbooks did not report major side effects of succinylcholine until 1960 and included newly documented side effects with each edition. BW Co.\u27s packaging contained warnings as early as the 1950\u27s but were later updated in 1962 and beyond to reflect the newly discovered hyperkalemia and malignant hyperthermia. Conclusion: Particularly given the regulatory environment of the time, BW Co. appropriately reported the adverse effects of succinylcholine after market entry; it updated promotional and packaging material in a timely manner to reflect newly discovered adverse effects. The toxicity, though alarming and put clinicians on alert, did not seem to heavily impact succinylcholine\u27s use, given its various desirable properties. It is still a choice muscle relaxant used today, although there are efforts to develop superior agents to replace succinylcholine

The AIM2 inflammasome is critical for innate immunity to Francisella tularensis.

Francisella tularensis, the causative agent of tularemia, infects host macrophages, which triggers production of the proinflammatory cytokines interleukin 1beta (IL-1beta) and IL-18. We elucidate here how host macrophages recognize F. tularensis and elicit this proinflammatory response. Using mice deficient in the DNA-sensing inflammasome component AIM2, we demonstrate here that AIM2 is required for sensing F. tularensis. AIM2-deficient mice were extremely susceptible to F. tularensis infection, with greater mortality and bacterial burden than that of wild-type mice. Caspase-1 activation, IL-1beta secretion and cell death were absent in Aim2(-/-) macrophages in response to F. tularensis infection or the presence of cytoplasmic DNA. Our study identifies AIM2 as a crucial sensor of F. tularensis infection and provides genetic proof of its critical role in host innate immunity to intracellular pathogens

CCR6, the Sole Receptor for the Chemokine CCL20, Promotes Spontaneous Intestinal Tumorigenesis

Interactions between the inflammatory chemokine CCL20 and its receptor CCR6 have been associated with colorectal cancer growth and metastasis, however, a causal role for CCL20 signaling through CCR6 in promoting intestinal carcinogenesis has not been demonstrated in vivo. In this study, we aimed to determine the role of CCL20-CCR6 interactions in spontaneous intestinal tumorigenesis. CCR6-deficient mice were crossed with mice heterozygous for a mutation in the adenomatous polyposis coli (APC) gene (APCMIN/+ mice) to generate APCMIN/+ mice with CCR6 knocked out (CCR6KO-APCMIN/+ mice). CCR6KO-APCMIN/+ mice had diminished spontaneous intestinal tumorigenesis. CCR6KO-APCMIN/+ also had normal sized spleens as compared to the enlarged spleens found in APCMIN/+ mice. Decreased macrophage infiltration into intestinal adenomas and non-tumor epithelium was observed in CCR6KO-APCMIN/+ as compared to APCMIN/+ mice. CCL20 signaling through CCR6 caused increased production of CCL20 by colorectal cancer cell lines. Furthermore, CCL20 had a direct mitogenic effect on colorectal cancer cells. Thus, interactions between CCL20 and CCR6 promote intestinal carcinogenesis. Our results suggest that the intestinal tumorigenesis driven by CCL20-CCR6 interactions may be driven by macrophage recruitment into the intestine as well as proliferation of neoplastic epithelial cells. This interaction could be targeted for the treatment or prevention of malignancy

Adaptive immunity restricts replication of novel murine astroviruses

The mechanisms of astrovirus pathogenesis are largely unknown, in part due to a lack of a small-animal model of disease. Using shotgun sequencing and a custom analysis pipeline, we identified two novel astroviruses capable of infecting research mice, murine astrovirus (MuAstV) STL1 and STL2. Subsequent analysis revealed the presence of at least two additional viruses (MuAstV STL3 and STL4), suggestive of a diverse population of murine astroviruses in research mice. Complete genomic characterization and subsequent phylogenetic analysis showed that MuAstV STL1 to STL4 are members of the mamastrovirus genus and are likely members of a new mamastrovirus genogroup. Using Rag1(−/−) mice deficient in B and T cells, we demonstrate that adaptive immunity is required to control MuAstV infection. Furthermore, using Stat1(−/−) mice deficient in innate signaling, we demonstrate a role for the innate immune response in the control of MuAstV replication. Our results demonstrate that MuAstV STL permits the study of the mechanisms of astrovirus infection and host-pathogen interactions in a genetically manipulable small-animal model. Finally, we detected MuAstV in commercially available mice, suggesting that these viruses may be present in academic and commercial research mouse facilities, with possible implications for interpretation of data generated in current mouse models of disease

Spectral structure and decompositions of optical states, and their applications

We discuss the spectral structure and decomposition of multi-photon states. Ordinarily `multi-photon states' and `Fock states' are regarded as synonymous. However, when the spectral degrees of freedom are included this is not the case, and the class of `multi-photon' states is much broader than the class of `Fock' states. We discuss the criteria for a state to be considered a Fock state. We then address the decomposition of general multi-photon states into bases of orthogonal eigenmodes, building on existing multi-mode theory, and introduce an occupation number representation that provides an elegant description of such states that in many situations simplifies calculations. Finally we apply this technique to several example situations, which are highly relevant for state of the art experiments. These include Hong-Ou-Mandel interference, spectral filtering, finite bandwidth photo-detection, homodyne detection and the conditional preparation of Schr\"odinger Kitten and Fock states. Our techniques allow for very simple descriptions of each of these examples.Comment: 12 page