Light-Dependent Electrogenic Activity of Cyanobacteria

Cyanobacteria account for 20-30% of Earth's primary photosynthetic productivity and convert solar energy into biomass-stored chemical energy at the rate of approximately 450 TW [1]. These single-cell microorganisms are resilient predecessors of all higher oxygenic phototrophs and can be found in self-sustaining, nitrogen-fixing communities the world over, from Antarctic glaciers to the Sahara desert [2].Here we show that diverse genera of cyanobacteria including biofilm-forming and pelagic strains have a conserved light-dependent electrogenic activity, i.e. the ability to transfer electrons to their surroundings in response to illumination. Naturally-growing biofilm-forming photosynthetic consortia also displayed light-dependent electrogenic activity, demonstrating that this phenomenon is not limited to individual cultures. Treatment with site-specific inhibitors revealed the electrons originate at the photosynthetic electron transfer chain (P-ETC). Moreover, electrogenic activity was observed upon illumination only with blue or red but not green light confirming that P-ETC is the source of electrons. The yield of electrons harvested by extracellular electron acceptor to photons available for photosynthesis ranged from 0.05% to 0.3%, although the efficiency of electron harvesting likely varies depending on terminal electron acceptor.The current study illustrates that cyanobacterial electrogenic activity is an important microbiological conduit of solar energy into the biosphere. The mechanism responsible for electrogenic activity in cyanobacteria appears to be fundamentally different from the one exploited in previously discovered electrogenic bacteria, such as Geobacter, where electrons are derived from oxidation of organic compounds and transported via a respiratory electron transfer chain (R-ETC) [3], [4]. The electrogenic pathway of cyanobacteria might be exploited to develop light-sensitive devices or future technologies that convert solar energy into limited amounts of electricity in a self-sustainable, CO(2)-free manner

The prion 2018 round tables (I): the structure of PrP Sc

Understanding the structure of PrPSc is without doubt a sine qua non to understand not only PrPSc propagation, but also critical features of that process such as the strain phenomenon and transmission barriers. While elucidation of the PrPSc structure has been full of difficulties, we now have a large amount of structural information that allows us to begin to understand it. This commentary article summarizes a round table that took place within the Prion 2018 meeting held in Santiago de Compostela to discuss the state of the art in this matter. Two alternative models of PrPSc exist: the PIRIBS and the 4-rung β-solenoid models. Both of them have relevant features. The 4-rung β-solenoid model agrees with experimental constraints of brain derived PrPSc obtained from cryo-EM and X-ray fiber diffraction studies. Furthermore, it allows facile accommodation of the bulky glycans that decorate brain-derived PrPSc. On the other hand, the infectious PrP23-144 amyloid exhibits a PIRIBS architecture. Perhaps, both types of structure co-exist.Supported by grants BFU2013-48436-C2-1-P and BFU2017- 86692-P from the Spanish Ministries of Economy and Competitiveness and Science, Innovation and Universities, respectively, to JRR and grant 201600029 from the Alberta Prion Research Institute to HW. This work was also supported in part by the Intramural Research Program of the NIAID (BC) and by the National Institute of Health grants R01 NS045585 (IVB), P01 AI106705 (WKS), R01 NS083687 (WKS) and R01 NS103848 (WKS)S

Genesis of Mammalian Prions: From Non-infectious Amyloid Fibrils to a Transmissible Prion Disease

The transmissible agent of prion disease consists of a prion protein in its abnormal, β-sheet rich state (PrPSc), which is capable of replicating itself according to the template-assisted mechanism. This mechanism postulates that the folding pattern of a newly recruited polypeptide chain accurately reproduces that of a PrPSc template. Here we report that authentic PrPSc and transmissible prion disease can be generated de novo in wild type animals by recombinant PrP (rPrP) amyloid fibrils, which are structurally different from PrPSc and lack any detectable PrPSc particles. When induced by rPrP fibrils, a long silent stage that involved two serial passages preceded development of the clinical disease. Once emerged, the prion disease was characterized by unique clinical, neuropathological, and biochemical features. The long silent stage to the disease was accompanied by significant transformation in neuropathological properties and biochemical features of the proteinase K-resistant PrP material (PrPres) before authentic PrPSc evolved. The current work illustrates that transmissible prion diseases can be induced by PrP structures different from that of authentic PrPSc and suggests that a new mechanism different from the classical templating exists. This new mechanism designated as “deformed templating” postulates that a change in the PrP folding pattern from the one present in rPrP fibrils to an alternative specific for PrPSc can occur. The current work provides important new insight into the mechanisms underlying genesis of the transmissible protein states and has numerous implications for understanding the etiology of neurodegenerative diseases

Synthetic prions generated in vitro are similar to a newly identified subpopulation of PrPSc from sporadic Creutzfeldt-Jakob disease

In recent studies, the amyloid form of recombinant prion protein (PrP) encompassing residues 89–230 (rPrP 89-230) produced in vitro induced transmissible prion disease in mice. These studies showed that unlike “classical” PrPSc produced in vivo, the amyloid fibrils generated in vitro were more proteinase-K sensitive. Here we demonstrate that the amyloid form contains a proteinase K-resistant core composed only of residues 152/153–230 and 162–230. The PK-resistant fragments of the amyloid form are similar to those observed upon PK digestion of a minor subpopulation of PrPSc recently identified in patients with sporadic Creutzfeldt-Jakob disease (CJD). Remarkably, this core is sufficient for self-propagating activity in vitro and preserves a β-sheet-rich fibrillar structure. Full-length recombinant PrP 23-230, however, generates two subpopulations of amyloid in vitro: One is similar to the minor subpopulation of PrPSc, and the other to classical PrPSc. Since no cellular factors or templates were used for generation of the amyloid fibrils in vitro, we speculate that formation of the subpopulation of PrPSc with a short PK-resistant C-terminal region reflects an intrinsic property of PrP rather than the influence of cellular environments and/or cofactors. Our work significantly increases our understanding of the biochemical nature of prion infectious agents and provides a fundamental insight into the mechanisms of prions biogenesis

Aβ Plaques Do Not Protect Against HSV-1 Infection in a Mouse Model of Familial Alzheimer’s Disease, and HSV-1 Does Not Induce Aβ Pathology in a Model of Late Onset Alzheimer’s Disease

The possibility that the etiology of late onset Alzheimer\u27s disease is linked to viral infections of the CNS has been actively debated in recent years. According to the antiviral protection hypothesis, viral pathogens trigger aggregation of Aβ peptides that are produced as a defense mechanism in response to infection to entrap and neutralize pathogens. To test the causative relationship between viral infection and Aβ aggregation, the current study examined whether Aβ plaques protect the mouse brain against Herpes Simplex Virus 1 (HSV-1) infection introduced via a physiological route and whether HSV-1 infection triggers formation of Aβ plaques in a mouse model of late-onset AD that does not develop Aβ pathology spontaneously. In aged 5XFAD mice infected via eye scarification, high density of Aβ aggregates did not improve survival time or rate when compared with wild type controls. In 5XFADs, viral replication sites were found in brain areas with a high density of extracellular Aβ deposits, however, no association between HSV-1 and Aβ aggregates could be found. To test whether HSV-1 triggers Aβ aggregation in a mouse model that lacks spontaneous Aβ pathology, 13-month-old hAβ/APOE4/Trem2*R47H mice were infected with HSV-1 via eye scarification with the McKrae HSV-1 strain, intracranial inoculation with McKrae, intracranial inoculation after priming with LPS for 6 weeks, or intracranial inoculation with high doses of McKrae or 17syn + strains that represent different degrees of neurovirulence. No signs of Aβ aggregation were found in any of the experimental groups. Instead, extensive infiltration of peripheral leukocytes was observed during the acute stage of HSV-1 infection, and phagocytic activity of myeloid cells was identified as the primary defense mechanism against HSV-1. The current results argue against a direct causative relationship between HSV-1 infection and Aβ pathology

Recombinant prion protein induces a new transmissible prion disease in wild-type animals

Prion disease is a neurodegenerative malady, which is believed to be transmitted via a prion protein in its abnormal conformation (PrPSc). Previous studies have failed to demonstrate that prion disease could be induced in wild-type animals using recombinant prion protein (rPrP) produced in Escherichia coli. Here, we report that prion infectivity was generated in Syrian hamsters after inoculating full-length rPrP that had been converted into the cross-β-sheet amyloid form and subjected to annealing. Serial transmission gave rise to a disease phenotype with highly unique clinical and neuropathological features. Among them were the deposition of large PrPSc plaques in subpial and subependymal areas in brain and spinal cord, very minor lesioning of the hippocampus and cerebellum, and a very slow progression of disease after onset of clinical signs despite the accumulation of large amounts of PrPSc in the brain. The length of the clinical duration is more typical of human and large animal prion diseases, than those of rodents. Our studies establish that transmissible prion disease can be induced in wild-type animals by inoculation of rPrP and introduce a valuable new model of prion diseases

Molecular Structure of Amyloid Fibrils Controls the Relationship between Fibrillar Size and Toxicity

According to the prevailing view, soluble oligomers or small fibrillar fragments are considered to be the most toxic species in prion diseases. To test this hypothesis, two conformationally different amyloid states were produced from the same highly pure recombinant full-length prion protein (rPrP). The cytotoxic potential of intact fibrils and fibrillar fragments generated by sonication from these two states was tested using cultured cells.For one amyloid state, fibril fragmentation was found to enhance its cytotoxic potential, whereas for another amyloid state formed within the same amino acid sequence, the fragmented fibrils were found to be substantially less toxic than the intact fibrils. Consistent with the previous studies, the toxic effects were more pronounced for cell cultures expressing normal isoform of the prion protein (PrP(C)) at high levels confirming that cytotoxicity was in part PrP(C)-dependent. Silencing of PrP(C) expression by small hairpin RNAs designed to silence expression of human PrP(C) (shRNA-PrP(C)) diminished the deleterious effects of the two amyloid states to a different extent, suggesting that the role of PrP(C)-mediated and PrP(C)-independent mechanisms depends on the structure of the aggregates.This work provides a direct illustration that the relationship between an amyloid's physical dimension and its toxic potential is not unidirectional but is controlled by the molecular structure of prion protein (PrP) molecules within aggregated states. Depending on the structure, a decrease in size of amyloid fibrils can either enhance or abolish their cytotoxic effect. Regardless of the molecular structure or size of PrP aggregates, silencing of PrP(C) expression can be exploited to reduce their deleterious effects

Protease-sensitive synthetic prions

Prions arise when the cellular prion protein (PrP(C)) undergoes a self-propagating conformational change; the resulting infectious conformer is designated PrP(Sc). Frequently, PrP(Sc) is protease-resistant but protease-sensitive (s) prions have been isolated in humans and other animals. We report here that protease-sensitive, synthetic prions were generated in vitro during polymerization of recombinant (rec) PrP into amyloid fibers. In 22 independent experiments, recPrP amyloid preparations, but not recPrP monomers or oligomers, transmitted disease to transgenic mice (n = 164), denoted Tg9949 mice, that overexpress N-terminally truncated PrP. Tg9949 control mice (n = 174) did not spontaneously generate prions although they were prone to late-onset spontaneous neurological dysfunction. When synthetic prion isolates from infected Tg9949 mice were serially transmitted in the same line of mice, they exhibited sPrP(Sc) and caused neurodegeneration. Interestingly, these protease-sensitive prions did not shorten the life span of Tg9949 mice despite causing extensive neurodegeneration. We inoculated three synthetic prion isolates into Tg4053 mice that overexpress full-length PrP; Tg4053 mice are not prone to developing spontaneous neurological dysfunction. The synthetic prion isolates caused disease in 600-750 days in Tg4053 mice, which exhibited sPrP(Sc). These novel synthetic prions demonstrate that conformational changes in wild-type PrP can produce mouse prions composed exclusively of sPrP(Sc)

Nonpathological Extracellular Amyloid Is Present during Normal Epididymal Sperm Maturation

Amyloids are aggregated proteins characterized by a specific cross-β-sheet structure and are typically associated with neurodegenerative diseases including Alzheimer's disease. Recently, however, several nonpathological amyloids have been found in intracellular organelles of normal mammalian tissues suggesting that amyloid may also carry out biological functions. We previously have shown that the epididymal cystatin CRES (cystatin-related epididymal spermatogenic), cst8, a reproductive-specific member of the cystatin superfamily of cysteine protease inhibitors, forms amyloid in vitro suggesting that CRES amyloid may also form in vivo within the epididymal lumen. Here we show that amyloid structures containing CRES are a component of the normal mouse epididymal lumen without any apparent cytotoxic effects on spermatozoa and that these structures change along the length of the tubule. These studies suggest the presence of a functional amyloid structure that may carry out roles in sperm maturation or maintenance of the luminal milieu and which itself may undergo maturational changes along the epididymis. In contrast to previous examples of functional amyloid which were intracellular, our studies now show that nonpathological/functional amyloid can also be extracellular. The presence of an extracellular and nonpathological amyloid in the epididymis suggests that similar amyloid structures may be present in other organ systems and may carry out distinctive tissue-specific functions