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- Genre: Doctoral Dissertation
Description
The F1Fo ATP synthase is required for energy conversion in almost all living organisms. The F1 complex is a molecular motor that uses ATP hydrolysis to drive rotation of the γ–subunit. It has not been previously possible to resolve the speed and position of the γ–subunit of the F1–ATPase as it rotates during a power stroke. The single molecule experiments presented here measured light scattered from 45X91 nm gold nanorods attached to the γ–subunit that provide an unprecedented 5 μs resolution of rotational position as a function of time. The product of velocity and drag, which were both measured directly, resulted in an average torque of 63±8 pN nm for the Escherichia coli F1-ATPase that was determined to be independent of the load. The rotational velocity had an initial (I) acceleration phase 15° from the end of the catalytic dwell, a slow (S) acceleration phase during ATP binding/ADP release (15°–60°), and a fast (F) acceleration phase (60°–90°) containing an interim deceleration (ID) phase (75°–82°). High ADP concentrations decreased the velocity of the S phase proportional to 'ADP-release' dwells, and the F phase proportional to the free energy derived from the [ADP][Pi]/[ATP] chemical equilibrium. The decreased affinity for ITP increased ITP-binding dwells by 10%, but decreased velocity by 40% during the S phase. This is the first direct evidence that nucleotide binding contributes to F1–ATPase torque. Mutations that affect specific phases of rotation were identified, some in regions of F1 previously considered not to contribute to rotation. Mutations βD372V and γK9I increased the F phase velocity, and γK9I increased the depth of the ID phase. The conversion between S and F phases was specifically affected by γQ269L. While βT273D, βD305E, and αR283Q decreased the velocity of all phases, decreases in velocity due to βD302T, γR268L and γT82A were confined to the I and S phases. The correlations between the structural locations of these mutations and the phases of rotation they affect provide new insight into the molecular basis for F1–ATPase γ-subunit rotation.
ContributorsMartin, James (Author) / Frasch, Wayne D (Thesis advisor) / Chandler, Douglas (Committee member) / Gaxiola, Roberto (Committee member) / Yan, Hao (Committee member) / Arizona State University (Publisher)
Created2012
Description
The basic scheme for photosynthesis suggests the two photosystems existing in parity with one another. However, cyanobacteria typically maintain significantly more photosystem I (PSI) than photosystem II (PSII) complexes. I set out to evaluate this disparity through development and analysis of multiple mutants of the genetically tractable cyanobacterium Synechocystis sp. PCC 6803 that exhibit a range of expression levels of the main proteins present in PSI (Chapter 2). One hypothesis was that the higher abundance of PSI in this organism is used to enable more cyclic electron flow (CEF) around PSI to contribute to greater ATP synthesis. Results of this study show that indeed CEF is enhanced by the high amount of PSI present in WT. On the other hand, mutants with less PSI and less cyclic electron flow appeared able to maintain healthy levels of ATP synthesis through other compensatory mechanisms. Reduction in PSI abundance is naturally associated with reduced chlorophyll content, and mutants with less PSI showed greater primary productivity as light intensity increased due to increased light penetration in the cultures. Another question addressed in this research project involved the effect of deletion of flavoprotein 3 (an electron sink for PSI-generated electrons) from mutant strains that produce and secrete a fatty acid (Chapter 3). Removing Flv3 increased fatty acid production, most likely due to increased abundance of reducing equivalents that are key to fatty acid biosynthesis. Additional components of my dissertation research included examination of alkane biosynthesis in Synechocystis (Chapter 4), and effects of attempting to overexpress fibrillin genes for enhancement of stored compounds (Chapter 5). Synechocystis is an excellent platform for metabolic engineering studies with its photosynthetic capability and ease of genetic alteration, and the presented research sheds light on multiple aspects of its fundamental biology.
ContributorsMoore, Vickie (Author) / Vermaas, Willem (Thesis advisor) / Wang, Xuan (Committee member) / Roberson, Robert (Committee member) / Gaxiola, Roberto (Committee member) / Bingham, Scott (Committee member) / Arizona State University (Publisher)
Created2017
Description
Climate change is making the arid southwestern U.S. (“Southwest”) warmer and drier. Decreases in water availability coupled with increases in episodic heat waves can pose extraordinary challenges for native riparian tree species to persist in their current ranges. However, the morpho-physiological mechanisms that these species deploy to cope with extreme temperature events are not well understood. Specifically, how do these species maintain leaf temperatures within a safe operational threshold in the extreme conditions found across the region? Morpho-physiological mechanisms influencing intraspecific local adaptation to thermal stress were assessed in Populus fremontii using two experimental common gardens. In a common garden located near the mid-point of this species’ thermal distribution, I studied coordinated traits that reflect selection for leaf thermal regulation through the measurement of 28 traits encompassing four different trait spectra: phenology, whole-tree architecture, and the leaf and wood economic spectrum. Also, I assessed how these syndromes resulted in more acquisitive and riskier water-use strategies that explained how warm-adapted populations exhibited lower leaves temperatures than cool-adapted populations. Then, I investigated if different water-use strategies are detectable at inter-annual temporal scales by comparing tree-ring growth, carbon, and oxygen isotopic measurements of cool- versus warm-adapted populations in a common garden located at the extreme hottest edge of P. fremontii’s thermal distribution. I found that P. fremontii’s adaptation to the extreme temperatures is explained by a highly intraspecific specialized trait coordination across multiple trait scales. Furthermore, I found that warmer-adapted populations displayed 39% smaller leaves, 38% higher midday stomatal conductance, reflecting 3.8 °C cooler mean leaf temperature than cool-adapted populations, but with the tradeoff of having 14% lower minimum leaf water potentials. In addition, warm-adapted genotypes at the hot edge of P. fremontii’s distribution had 20% higher radial growth rates, although no differences were detected in either carbon or oxygen isotope ratios indicating that differences in growth may not have reflected seasonal differences in photosynthetic gas exchange. These studies describe the potential effect that extreme climate might have on P. fremontii’s survival, its intraspecific responses to those events, and which traits will be advantageous to cope with those extreme environmental conditions.
ContributorsBlasini, Davis E (Author) / Hultine, Kevin R (Thesis advisor) / Day, Thomas A (Thesis advisor) / Ogle, Kiona (Committee member) / Throop, Heather (Committee member) / Gaxiola, Roberto (Committee member) / Arizona State University (Publisher)
Created2022
Description
Cocaine abuse affects millions of people with disastrous medical and societal consequences. Despite this, there is still no FDA-approved treatment to decrease the likelihood of relapse in rehabilitated addicts, and acute cocaine toxicity (overdose) is only symptomatically treated. Studies have demonstrated a promising potential treatment option with the help of the human serum enzyme butyrylcholinesterase (BChE), an enzyme capable of breaking down cocaine into biologically inactive side products. This activity of wild-type BChE, however, is relatively low. This prompted the design of variants of BChE which exhibit significantly improved catalytic activity against cocaine. Plants were used as a sustainable, scalable, affordable platform system to produce large amounts of human biologics such as these cocaine hydrolase variants of BChE. Using a tobacco relative, Nicotiana benthamiana, recombinant enzymes can be produced at quantities relevant to clinical use with desired kinetic properties. Next, the ability of the most promising plant-produced cocaine super hydrolase, pCocSH, to counter the lethal effects of cocaine overdose in vivo was tested. These studies revealed that this plant-produced enzyme can protect mice from an otherwise lethal dose of cocaine. Most excitingly, it was found that pCocSH can rescue mice from overdose when given immediately after the onset of cocaine-induced seizures. These studies provide in vitro and in vivo proof-of-principle for a promising plant-derived biologic to be used as a pharmacokinetic-based treatment for cocaine addiction-related diseases such as overdose.
ContributorsLarrimore, Katherine E (Author) / Mor, Tsafrir S (Thesis advisor) / Gaxiola, Roberto (Committee member) / Mason, Hugh S (Committee member) / Neisewander, Janet L (Committee member) / Arizona State University (Publisher)
Created2015