Excitation energy transfer to Photosystem I in filaments and heterocysts of Nostoc punctiforme

AbstractCyanobacteria adapt to varying light conditions by controlling the amount of excitation energy to the photosystems. On the minute time scale this leads to redirection of the excitation energy, usually referred to as state transitions, which involves movement of the phycobilisomes. We have studied short-term light adaptation in isolated heterocysts and intact filaments from the cyanobacterium Nostoc punctiforme ATCC 29133. In N.punctiforme vegetative cells differentiate into heterocysts where nitrogen fixation takes place. Photosystem II is inactivated in the heterocysts, and the abundancy of Photosystem I is increased relative to the vegetative cells. To study light-induced changes in energy transfer to Photosystem I, pre-illumination was made to dark adapted isolated heterocysts. Illumination wavelengths were chosen to excite Photosystem I (708nm) or phycobilisomes (560nm) specifically. In heterocysts that were pre-illuminated at 708nm, fluorescence from the phycobilisome terminal emitter was observed in the 77K emission spectrum. However, illumination with 560nm light caused quenching of the emission from the terminal emitter, with a simultaneous increase in the emission at 750nm, indicating that the 560nm pre-illumination caused trimerization of Photosystem I. Excitation spectra showed that 560nm pre-illumination led to an increase in excitation transfer from the phycobilisomes to trimeric Photosystem I. Illumination at 708nm did not lead to increased energy transfer from the phycobilisome to Photosystem I compared to dark adapted samples. The measurements were repeated using intact filaments containing vegetative cells, and found to give very similar results as the heterocysts. This demonstrates that molecular events leading to increased excitation energy transfer to Photosystem I, including trimerization, are independent of Photosystem II activity

Artificial Photosynthesis for Solar Fuels - an Evolving Research Field within AMPEA, a Joint Programme of the European Energy Research Alliance

On the path to an energy transition away from fossil fuels to sustainable sources, the European Union is for the moment keeping pace with the objectives of the Strategic Energy Technology-Plan. For this trend to continue after 2020, scientific breakthroughs must be achieved. One main objective is to produce solar fuels from solar energy and water in direct processes to accomplish the efficient storage of solar energy in a chemical form. This is a grand scientific challenge. One important approach to achieve this goal is Artificial Photosynthesis. The European Energy Research Alliance has launched the Joint Programme "Advanced Materials & Processes for Energy Applications” (AMPEA) to foster the role of basic science in Future Emerging Technologies. European researchers in artificial photosynthesis recently met at an AMPEA organized workshop to define common research strategies and milestones for the future. Through this work artificial photosynthesis became the first energy research sub-field to be organised into what is designated "an Application” within AMPEA. The ambition is to drive and accelerate solar fuels research into a powerful European field - in a shorter time and with a broader scope than possible for individual or national initiatives. Within AMPEA the Application Artificial Photosynthesis is inclusive and intended to bring together all European scientists in relevant fields. The goal is to set up a thorough and systematic programme of directed research, which by 2020 will have advanced to a point where commercially viable artificial photosynthetic devices will be under development in partnership with industr

Csnk1a1 inhibition has p53-dependent therapeutic efficacy in acute myeloid leukemia

Despite extensive insights into the underlying genetics and biology of acute myeloid leukemia (AML), overall survival remains poor and new therapies are needed. We found that casein kinase 1 α (Csnk1a1), a serine-threonine kinase, is essential for AML cell survival in vivo. Normal hematopoietic stem and progenitor cells (HSPCs) were relatively less affected by shRNA-mediated knockdown of Csnk1a1. To identify downstream mediators of Csnk1a1 critical for leukemia cells, we performed an in vivo pooled shRNA screen and gene expression profiling. We found that Csnk1a1 knockdown results in decreased Rps6 phosphorylation, increased p53 activity, and myeloid differentiation. Consistent with these observations, p53-null leukemias were insensitive to Csnk1a1 knockdown. We further evaluated whether D4476, a casein kinase 1 inhibitor, would exhibit selective antileukemic effects. Treatment of leukemia stem cells (LSCs) with D4476 showed highly selective killing of LSCs over normal HSPCs. In summary, these findings demonstrate that Csnk1a1 inhibition causes reduced Rps6 phosphorylation and activation of p53, resulting in selective elimination of leukemia cells, revealing Csnk1a1 as a potential therapeutic target for the treatment of AML

Highlights From the Annual Meeting of the American Epilepsy Society 2022

With more than 6000 attendees between in-person and virtual offerings, the American Epilepsy Society Meeting 2022 in Nashville, felt as busy as in prepandemic times. An ever-growing number of physicians, scientists, and allied health professionals gathered to learn a variety of topics about epilepsy. The program was carefully tailored to meet the needs of professionals with different interests and career stages. This article summarizes the different symposia presented at the meeting. Basic science lectures addressed the primary elements of seizure generation and pathophysiology of epilepsy in different disease states. Scientists congregated to learn about anti-seizure medications, mechanisms of action, and new tools to treat epilepsy including surgery and neurostimulation. Some symposia were also dedicated to discuss epilepsy comorbidities and practical issues regarding epilepsy care. An increasing number of patient advocates discussing their stories were intertwined within scientific activities. Many smaller group sessions targeted more specific topics to encourage member participation, including Special Interest Groups, Investigator, and Skills Workshops. Special lectures included the renown Hoyer and Lombroso, an ILAE/IBE joint session, a spotlight on the impact of Dobbs v. Jackson on reproductive health in epilepsy, and a joint session with the NAEC on coding and reimbursement policies. The hot topics symposium was focused on traumatic brain injury and post-traumatic epilepsy. A balanced collaboration with the industry allowed presentations of the latest pharmaceutical and engineering advances in satellite symposia

Review of the algal biology program within the National Alliance for Advanced Biofuels and Bioproducts

In 2010,when the National Alliance for Advanced Biofuels and Bioproducts (NAABB) consortiumbegan, littlewas known about themolecular basis of algal biomass or oil production. Very fewalgal genome sequenceswere available and efforts to identify the best-producing wild species through bioprospecting approaches had largely stalled after the U.S. Department of Energy\u27s Aquatic Species Program. This lack of knowledge included how reduced carbon was partitioned into storage products like triglycerides or starch and the role played bymetabolite remodeling in the accumulation of energy-dense storage products. Furthermore, genetic transformation and metabolic engineering approaches to improve algal biomass and oil yields were in their infancy. Genome sequencing and transcriptional profiling were becoming less expensive, however; and the tools to annotate gene expression profiles under various growth and engineered conditions were just starting to be developed for algae. It was in this context that an integrated algal biology program was introduced in the NAABB to address the greatest constraints limiting algal biomass yield. This review describes the NAABB algal biology program, including hypotheses, research objectives, and strategies to move algal biology research into the twenty-first century and to realize the greatest potential of algae biomass systems to produce biofuels

Heterocyst Thylakoid Bioenergetics

Heterocysts are specialized cells that differentiate in the filaments of heterocystous cyanobacteria. Their role is to maintain a microoxic environment for the nitrogenase enzyme during diazotrophic growth. The lack of photosynthetic water oxidation in the heterocyst puts special constraints on the energetics for nitrogen fixation, and the electron transport pathways of heterocyst thylakoids are slightly different from those in vegetative cells. During recent years, there has been a growing interest in utilizing heterocysts as cell factories for the production of fuels and other chemical commodities. Optimization of these production systems requires some consideration of the bioenergetics behind nitrogen fixation. In this overview, we emphasize the role of photosynthetic electron transport in providing ATP and reductants to the nitrogenase enzyme, and provide some examples where heterocysts have been used as production facilities

Electron Donor Systems in Natural and Artificial Photosynthesis

Photosynthesis is the process by which light energy is converted into chemical products, in photoautotrophic bacteria, algae and plants. The principal idea is the production of reducing agents by photo-induced oxidation of a sacrificial electron donor. Photosystem II in plants, algae and cyanobacteria, absorbs light and catalyzes the oxidation of water, liberating electrons that are used to form reductants. By capturing light, plants and algae provide the entire biosphere with an electron source for the buildup of living tissue. The active site for photosynthetic water oxidation contains a tetranuclear manganese cluster and a redox active tyrosyl residue. Together with the photosensitizer chlorophylls in the reaction center of Photosystem II, the manganese and the tyrosine activate and split water molecules into molecular oxygen, electrons and protons. In the first part of this thesis the nature of the manganese binding site, and the electron transfer reactions involved in the assembly of the manganese cluster were investigated. Selective chemical modification of histidyl and carboxylic acid residues was conducted on the manganese binding area of Photosystem II. Kinetic studies of manganese binding after chemical modification revealed binding sites with different affinity for manganese. Two binding sites containing histidines were found, and two or more sites of carboxylic acid residues. The participation of the redox active cofactors Tyrosine-D and cytochrome-b559 in the activation of the water oxidizing center was studied using EPR spectroscopy. Tyrosine-D and cytochrome-b559 was found to aid Photosystem II in the assembly of a functional manganese cluster, by acting as auxilliary electron donors, and in the case of cytochrome-b559 under high light intensities, also as auxilliary electron acceptor. The two cofactors thereby prevent light-induced protein damadge during activation of the water oxidizing complex. In the second part of the thesis, the properties and reactions of novel compounds, synthesized with the objective to mimic the water oxidizing complex, were studied by optical and EPR spectroscopy. A ruthenium complex, serving as photosensitizer, was covalently connetced to a tyrosine. Light-induced electron transfer from the tyrosine to the ruthenium part was generated in the complex, similar to the reactions in Photosystem II. This super-molecule was then allowed to react with a synthetic dinuclear manganese complex. Electron transfer from manganese to the photooxidized tyrosine was observed, thereby mimicking the stepwise electron transfer reactions that take place on the electron donor side of Photosystem II. This is the first functional mimic of the water oxidizing triad in Photosystem II, and a new platform for regenerative electron donor systems in artificial photosynthesis

Healing of tympanic membrane after myringotomy during Streptococcus pneumoniae otitis media : An otomicroscopic and histologic study in the rat

The purpose of our study was to elucidate the course of healing of the tympanic membrane (TM) when myringotomy was performed during acute otitis media. The early and long-lasting structural changes of the TM were studied in an animal model. Rats were inoculated with Streptococcus pneumoniae (PnC) type 3 in the bulla. When the infection was manifest, myringotomy was performed. On days 4 and 12, and 3 and 6 months after myringotomy, the TM status was checked by otomicroscopy and TMs were prepared for light and electron microscopy. Comparison was made with PnC-infected TMs that were not perforated, as well as myringotomized noninfected TMs. The infection resolved more slowly in myringotomized ears compared to PnC-infected ears that were left untouched. After 6 months, the pars tensa of the myringotomized infected ears was thickened and showed a disorganized collagen structure, compared with myringotomized noninfected ears, in which TMs were normalized. The PnC- infected TMs without myringotomy were completely normalized after 2 months. We conclude that a combination of bacterial infection and myringotomy causes long-lasting changes in TM structure. This impaired structure of the connective tissue could be of importance in chronic middle ear disease as a presumptive site for retraction and perforation of the TM