Functional expression and evaluation of heterologous phosphoketolases in Saccharomyces cerevisiae

Phosphoketolases catalyze an energy-and redox-independent cleavage of certain sugar phosphates. Hereby, the two-carbon (C2) compound acetyl-phosphate is formed, which enzymatically can be converted into acetyl-CoA-a key precursor in central carbon metabolism. Saccharomyces cerevisiae does not demonstrate efficient phosphoketolase activity naturally. In this study, we aimed to compare and identify efficient heterologous phosphoketolase enzyme candidates that in yeast have the potential to reduce carbon loss compared to the native acetyl-CoA producing pathway by redirecting carbon flux directly from C5 and C6 sugars towards C2-synthesis. Nine phosphoketolase candidates were expressed in S. cerevisiae of which seven produced significant amounts of acetyl-phosphate after provision of sugar phosphate substrates in vitro. The candidates showed differing substrate specificities, and some demonstrated activity levels significantly exceeding those of candidates previously expressed in yeast. The conducted studies also revealed that S. cerevisiae contains endogenous enzymes capable of breaking down acetyl-phosphate, likely into acetate, and that removal of the phosphatases Gpp1 and Gpp2 could largely prevent this breakdown. An evaluation of in vivo function of a subset of phosphoketolases was conducted by monitoring acetate levels during growth, confirming that candidates showing high activity in vitro indeed showed increased acetate accumulation, but expression also decreased cellular fitness. The study shows that expression of several bacterial phosphoketolase candidates in S. cerevisiae can efficiently divert intracellular carbon flux toward C2-synthesis, thus showing potential to be used in metabolic engineering strategies aimed to increase yields of acetyl-CoA derived compounds

Electronic excitation dynamics in multichromophoric systems described via a polaron-representation master equation

We derive a many-site version of the non-Markovian time-convolutionless polaron master equation [S. Jang et al., J. Chem Phys. 129, 101104 (2008)] to describe electronic excitation dynamics in multichromophoric systems. By treating electronic and vibrational degrees of freedom in a combined frame (polaron frame), this theory is capable of interpolating between weak and strong exciton-phonon coupling and is able to account for initial non-equilibrium bath states and spatially correlated environments. Besides outlining a general expression for the expected value of any electronic system observable in the original frame, we also discuss implications of the Markovian and secular approximations highlighting that they need not hold in the untransformed frame despite being strictly satisfied in the polaron frame. The key features of the theory are illustrated using as an example a four-site subsystem of the Fenna-Mathew-Olson light-harvesting complex. For a spectral density including a localised high-energy mode, we show that oscillations of site populations may only be observed when non-equilibrium bath effects are taken into account. Furthermore, we illustrate how this formalism allows us to identify the electronic or vibrational origin of the oscillatory dynamics.Comment: 13 pages, 6 figures; minor corrections made; accepted for publication in Journal of Chemical Physic

Formación de profesores y conocimientos sobre estudiantes de alta capacidad

Apresenta-se reflexão acerca do processo (in)formativo e práxis de agentes educacionais (n = 15) de duas escolas de duas cidades de pequeno porte no Condado de Tippecanoe, no estado de Indiana, Estados Unidos, no tocante aos estudantes com Altas Habilidades/Superdotação. Os dados foram analisados por meio da Análise de Conteúdo, com o apoio do Software IRAMUTEQ. Os participantes revelaram-se distantes do perfil geral dos agentes educacionais brasileiros, os quais se colocam como dependentes das intervenções legais, são passivos no seu processo de (in)formação e alienados para a práxis de diferenciação instrucional e curricular, que desconsidera os diferentes níveis e perfis dos estudantes. Diversamente, a práxis dos participantes assenta-se na formação básica que considera imprescindível o desenvolvimento pleno de seus estudantes e em níveis de excelência.Reflection on the (in)formative process and praxis of educational agents of two schools in two small cities in Tippecanoe County, state of Indiana, United States, about gifted and talented/high-ability students. Data from interviews carried out with 15 educators related to these schools and cities were analyzed through Bardin’s Content Analysis, using the IRAMUTEQ Software, which analyzed seven corpora, related to the research block - Teacher training and knowledge about high-ability students. The participants revealed themselves to be distant from the general profile of Brazilian educational agents, who place themselves as dependent on legal interventions, are passive in their (in)training process and alienated to the instructional and curricular differentiation praxis, which disregards the different levels and student profiles. In contrast, the praxis of the participants is based on basic training that considers the full development of their students and levels of excellence essential.Se presenta una reflexión sobre el proceso (in)formativo y la praxis de los agentes educativos de dos escuelas en dos ciudades pequeñas en el condado de Tippecanoe, estado de Indiana, Estados Unidos, con respecto a los estudiantes superdotados. Los datos de las entrevistas realizadas a 15 agentes educativos relacionados con estas escuelas y ciudades fueron analizados mediante el Análisis de Contenido de Bardin, con el apoyo del Software IRAMUTEQ, que analizó siete corpus, relacionados con el bloque temático - Teacher training and conocimiento sobre los estudiantes de alta capacidad. Los participantes se revelaron distantes del perfil general de los agentes educativos brasileños, quienes se colocan como dependientes de las intervenciones legales, son pasivos en su proceso (in)formativo de capacitación y están alienados de la práctica de la diferenciación instructiva y curricular, que ignora los diferentes niveles y perfiles de estudiantes. Por el contrario, la praxis de los participantes se basa en una formación básica que considera esencial el pleno desarrollo de sus alumnosy sus niveles de excelencia

Irrealis i engelsk, dansk og tysk - en grammatisk kategori uden systemisk adresse

This paper is concerned with the apparent absence of a ‘systemic address’ for the functional category irrealis in grammatical descriptions of English, Danish and German within the framework of systemic functional linguistics (SFL). Based on a thorough discussion of our understanding of this functional grammatical concept, we present a summary of the lexicogrammatical potential of irrealis in English, Danish and German. By comparing and contrasting the three languages, we find among them equivalent connections to other grammatical systems. The existing SFL-descriptions of English, Danish and German offer some proposals with regard to irrealis, but these, to some degree, contradict our findings concerning how irrealis is actually realized. Hence, we discuss if and how irrealis can be combined with other grammatical systems like CLAUSE STATUS, POLARITY and MODALITY TYPES in the interpersonal grammar of the clause, which leads to a suggestion on how to incorporate irrealis in the MOOD-system

Determination of the noise parameters in a one-dimensional open quantum system

We consider an electron magnetically interacting with a spin-1/2 impurity, embedded in an external environment whose noisy term acts only on the impurity's spin, and we find expressions for the electron transmission and reflection probabilities in terms of the phenomenological noise parameters. Moreover, we give a simple example of the necessity of complete positivity for physical consistency, showing that a positive but not completely positive dissipative map can lead to negative transmission probabilities

Illusory Sensation of Movement Induced by Repetitive Transcranial Magnetic Stimulation

Human movement sense relies on both somatosensory feedback and on knowledge of the motor commands used to produce the movement. We have induced a movement illusion using repetitive transcranial magnetic stimulation over primary motor cortex and dorsal premotor cortex in the absence of limb movement and its associated somatosensory feedback. Afferent and efferent neural signalling was abolished in the arm with ischemic nerve block, and in the leg with spinal nerve block. Movement sensation was assessed following trains of high-frequency repetitive transcranial magnetic stimulation applied over primary motor cortex, dorsal premotor cortex, and a control area (posterior parietal cortex). Magnetic stimulation over primary motor cortex and dorsal premotor cortex produced a movement sensation that was significantly greater than stimulation over the control region. Movement sensation after dorsal premotor cortex stimulation was less affected by sensory and motor deprivation than was primary motor cortex stimulation. We propose that repetitive transcranial magnetic stimulation over dorsal premotor cortex produces a corollary discharge that is perceived as movement