Electromagnetically Clean Solar Arrays

The term 'electromagnetically clean solar array' ('EMCSA') refers to a panel that contains a planar array of solar photovoltaic cells and that, in comparison with a functionally equivalent solar-array panel of a type heretofore used on spacecraft, (1) exhibits less electromagnetic interferences to and from other nearby electrical and electronic equipment and (2) can be manufactured at lower cost. The reduction of electromagnetic interferences is effected through a combination of (1) electrically conductive, electrically grounded shielding and (2) reduction of areas of current loops (in order to reduce magnetic moments). The reduction of cost is effected by designing the array to be fabricated as a more nearly unitary structure, using fewer components and fewer process steps. Although EMCSAs were conceived primarily for use on spacecraft they are also potentially advantageous for terrestrial applications in which there are requirements to limit electromagnetic interference. In a conventional solar panel of the type meant to be supplanted by an EMCSA panel, the wiring is normally located on the back side, separated from the cells, thereby giving rise to current loops having significant areas and, consequently, significant magnetic moments. Current-loop geometries are chosen in an effort to balance opposing magnetic moments to limit far-0field magnetic interactions, but the relatively large distances separating current loops makes full cancellation of magnetic fields problematic. The panel is assembled from bare photovoltaic cells by means of multiple sensitive process steps that contribute significantly to cost, especially if electomagnetic cleanliness is desired. The steps include applying a cover glass and electrical-interconnect-cell (CIC) sub-assemble, connecting the CIC subassemblies into strings of series-connected cells, laying down and adhesively bonding the strings onto a panel structure that has been made in a separate multi-step process, and mounting the wiring on the back of the panel. Each step increases the potential for occurrence of latent defects, loss of process control, and attrition of components. An EMCSA panel includes an integral cover made from a transparent material. The silicone cover supplants the individual cover glasses on the cells and serves as an additional unitary structural support that offers the advantage, relative to glass, of the robust, forgiving nature of the silcone material. The cover contains pockets that hold the solar cells in place during the lamination process. The cover is coated with indium tin oxide to make its surface electrically conductive, so that it serves as a contiguous, electrically grounded shield over the entire panel surface. The cells are mounted in proximity to metallic printed wiring. The painted-wiring layer comprises metal-film traces on a sheet of Kapton (or equivalent) polyimide. The traces include contact pads on one side of the sheet for interconnecting the cells. Return leads are on the opposite side of the sheet, positioned to form the return currents substantially as mirror images of, and in proximity to, the cell sheet currents, thereby minimizing magnetic moments. The printed-wiring arrangement mimics the back-wiring arrangement of conventional solar arrays, but the current-loop areas and the resulting magnetic moments are much smaller because the return-current paths are much closer to the solar-cell sheet currents. The contact pads are prepared with solder fo electrical and mechanical bonding to the cells. The pocketed cover/shield, the solar cells, the printed-wiring layer, an electrical bonding agent, a mechanical-bonding agent, a composite structural front-side face sheet, an aluminum honeycomb core, and a composite back-side face sheet are all assembled, then contact pads are soldered to the cells and the agents are cured in a single lamination process

Subunit asymmetry and roles of conformational switching in the hexameric AAA+ ring of ClpX

The hexameric AAA+ ring of Escherichia coli ClpX, an ATP-dependent machine for protein unfolding and translocation, functions with the ClpP peptidase to degrade target substrates. For efficient function, ClpX subunits must switch between nucleotide-loadable (L) and nucleotide-unloadable (U) conformations, but the roles of switching are uncertain. Moreover, it is controversial whether working AAA+-ring enzymes assume symmetric or asymmetric conformations. Here, we show that a covalent ClpX ring with one subunit locked in the U conformation catalyzes robust ATP hydrolysis, with each unlocked subunit able to bind and hydrolyze ATP, albeit with highly asymmetric position-specific affinities. Preventing U↔L interconversion in one subunit alters the cooperativity of ATP hydrolysis and reduces the efficiency of substrate binding, unfolding and degradation, showing that conformational switching enhances multiple aspects of wild-type ClpX function. These results support an asymmetric and probabilistic model of AAA+-ring activity.National Institutes of Health (U.S.) (Grant GM-101988)Massachusetts Institute of Technology (Poitras Predoctoral Fellowship

Kenneth Burke, the Basic Communication Course, and Applied Scholarship

The Journal of Applied Communication Research published a forum of position papers in 2000 (Volume 28, Issue 2) that sought to define “applied communication research.” Collectively, the authors called for scholarship that embodies a reflexive relationship between theory and practice (O’Hair, 2000; Keyton, 2000, Cissna, 2000; Eadie, 2000; Frey, 2000; Seibold, 2000; Wood, 2000). In this essay, we call for applied scholarship that focuses on how we talk, perform, and theorize the basic communication course. Drawing from the works of Kenneth Burke (e.g., 1931/1968; 1935; 1937/1984; 1941/ 1967; 1945/1969; 1954/1984), we focus specifically on the salience of discourses of and about the basic communication course and communication enriched courses across general education and liberal studies curricula

Substrate denaturation and translocation by a proteolytic machine

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 2005.Includes bibliographical references.Many AAA+ molecular machines generate power and drive cellular processes by harnessing energy from cycles of ATP hydrolysis. ClpX is a relatively simple AAA+ ATPase that powers regulated protein degradation by binding native protein substrates, denaturing them, and translocating the unfolded molecule into the sequestered proteolytic compartment of its peptidase partner, ClpP. Mechanistic studies of ClpXP degradation provide insight into energy-dependent proteolysis and may help elucidate how other AAA+ motors function as well. By studying the ClpXP-mediated degradation of model substrates in native and denatured forms, I investigated the role of both substrate stability and ATP consumption during the individual substrate processing steps of this protease. My results demonstrate that the rate of substrate proteolysis by ClpXP correlates poorly with global thermodynamic stability, but instead appears to be influenced by the local stability of protein structure adjacent to the degradation tag, as well as the location of the tag within this individual local element. These findings support a directional unfolding mechanism whereby ClpXP denatures proteins by first peeling apart the structural elements that abut the recognition tag. Analysis of ATP consumption during denaturation and translocation reveals how the ClpXP motor operates during these ClpXP processing steps. ATP turnover rates are relatively fast during substrate translocation, utilizing about 1 ATP molecule per amino acid translocated. In contrast, ATP hydrolysis remains at a reduced but constant rate during the denaturation of native substrates independent of their intrinsic stability, but requires the hydrolysis of increasing numbers of ATP molecules as the stability of the substrate also increases.(cont.) These findings suggest that ClpXP is capable of denaturing very stable proteins by applying repeated cycles of an unfolding force linked to the cycles of ATP hydrolysis. Competition experiments further reveal that stable substrates are frequently released from CIpXP when they resist denaturation, but unstable substrates are rapidly engaged by the proteolytic machinery. This preference prevents ClpXP from being jammed with substrates that are difficult to unfold. Moreover, it allows the protease to selectively degrade poorly structured substrates that consequently require fewer cycles of ATP hydrolysis, thereby ensuring that the energy of ATP hydrolysis is used efficiently for protein degradation. These mechanistic features could be useful for other AAA+ ATPases that translocate polymers against a force.by Jon Anders Kenniston.Ph.D

Control of substrate gating and translocation into ClpP by channel residues and ClpX binding

ClpP is a self-compartmentalized protease, which has very limited degradation activity unless it associates with ClpX to form ClpXP or with ClpA to form ClpAP. Here, we show that ClpX binding stimulates ClpP cleavage of peptides larger than a few amino acids and enhances ClpP active-site modification. Stimulation requires ATP binding but not hydrolysis by ClpX. The magnitude of this enhancement correlates with increasing molecular weight of the molecule entering ClpP. Amino-acid substitutions in the channel loop or helix A of ClpP enhance entry of larger substrates into the free enzyme, eliminate ClpX binding in some cases, and are not further stimulated by ClpX binding in other instances. These results support a model in which the channel residues of free ClpP exclude efficient entry of all but the smallest peptides into the degradation chamber, with ClpX binding serving to relieve these inhibitory interactions. Specific ClpP channel variants also prevent ClpXP translocation of certain amino-acid sequences, suggesting that the wild-type channel plays an important role in facilitating broad translocation specificity. In combination with previous studies, our results indicate that collaboration between ClpP and its partner ATPases opens a gate that functions to exclude larger substrates from isolated ClpP.National Institutes of Health (U.S.) (Grant number AI-15706

Mechanochemical basis of protein degradation by a double-ring AAA+ machine

Molecular machines containing double or single AAA+ rings power energy-dependent protein degradation and other critical cellular processes, including disaggregation and remodeling of macromolecular complexes. How the mechanical activities of double-ring and single-ring AAA+ enzymes differ is unknown. Using single-molecule optical trapping, we determine how the double-ring ​ClpA enzyme from Escherichia coli, in complex with the ​ClpP peptidase, mechanically degrades proteins. We demonstrate that ​ClpA unfolds some protein substrates substantially faster than does the single-ring ​ClpX enzyme, which also degrades substrates in collaboration with ​ClpP. We find that ​ClpA is a slower polypeptide translocase and that it moves in physical steps that are smaller and more regular than steps taken by ​ClpX. These direct measurements of protein unfolding and translocation define the core mechanochemical behavior of a double-ring AAA+ machine and provide insight into the degradation of proteins that unfold via metastable intermediates.Howard Hughes Medical InstituteNational Institutes of Health (U.S.) (Grant AI-16892

Tetravalent SARS-CoV-2 S1 Subunit Protein Vaccination Elicits Robust Humoral and Cellular Immune Responses in SIV-Infected Rhesus Macaque Controllers

The study provides important insights into the immunogenicity and efficacy of a tetravalent protein subunit vaccine candidate against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The vaccine induced both humoral and cellular immune responses in nonhuman primates with controlled SIVagm infection and was able to generate Omicron variant-specific antibodies without specifically vaccinating with Omicron. These findings suggest that the tetravalent composition of the vaccine candidate could provide broad protection against multiple SARS-CoV-2 variants while minimizing the risk of immune escape and the emergence of new variants. Additionally, the use of rhesus macaques with controlled SIVsab infection may better represent vaccine immunogenicity in humans with chronic viral diseases, highlighting the importance of preclinical animal models in vaccine development. Overall, the study provides valuable information for the development and implementation of coronavirus disease 2019 vaccines, particularly for achieving global vaccine equity and addressing emerging variants

Microneedle array delivered recombinant coronavirus vaccines: Immunogenicity and rapid translational development

Background: Coronaviruses pose a serious threat to global health as evidenced by Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), and COVID-19. SARS Coronavirus (SARS-CoV), MERS Coronavirus (MERS-CoV), and the novel coronavirus, previously dubbed 2019-nCoV, and now officially named SARS-CoV-2, are the causative agents of the SARS, MERS, and COVID-19 disease outbreaks, respectively. Safe vaccines that rapidly induce potent and long-lasting virus-specific immune responses against these infectious agents are urgently needed