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The complete λ-carrageenan depolymerization cascade from a marine Pseudoalteromonad revealed by structural analysis of the enzymes
Get PDFFunding: This research was supported by a Natural Sciences and Engineering Research Council of Canada Discovery Grant (FRN 04355).Carrageenans are a complex group of polysaccharides derived from the cell walls of red macroalgae. They are an abundant, yet recalcitrant nutrient source for most marine heterotrophic bacteria. Some member species of the Pseudoalteromonas genus are effective at metabolizing carrageenan. However, the enzymatic pathway for λ-carrageenan, one of the most sulfated naturally occurring polysaccharides, remains unknown. Using detailed structural analysis by X-ray crystallography we reveal the sophisticated and cyclic enzymatic cascade deployed by Pseudoalteromonas distincta (strain U2A) to utilize λ-carrageenan. The cascade incorporates ten glycoside hydrolases and five sulfatases that are specific for λ-carrageenan and cooperate to completely deconstruct this polysaccharide, thus yielding galactose monosaccharides for subsequent energy production. The detailed molecular understanding of λ-carrageenan depolymerisation provided includes structural evidence for a lesser described sulfatase catalytic mechanism and elucidation of a distinct catabolic cascade that is unique from previously described carrageenan metabolic pathways. This insight also holds potential for the application of enzymatic logic in the generation of high value products from abundant natural biopolymers, such as carrageenans.Peer reviewe
Mesoarchaean peridotite-norite cumulates of SW Greenland – the Miaggoq ultramafic complex
No full textFunding: This study was funded by VILLUM FONDEN through Grant VKR18978 awarded to Kristoffer Szilas.Several studies focused on the ultramafic bodies of the Archaean continental crust in southern Greenland in order to gain information on early Earth petrogenetic, metamorphic and metasomatic processes. This research provides the first petrological dataset of the Miaggoq Ultramafic Complex (∼1 km2) in the Akia terrane, with a minimum age of 2997 ± 15 Ma. It comprises ultramafic (dunite, peridotite) and mafic (orthopyroxenite, norite) rocks along with chromitites and provides a window into Mesoarchaean mantle compositions. Field observations, such as chromitite bands, mineral layering, and orthopyroxenite oikocrysts in peridotites coupled with chemical analysis displaying high abundance of chromites in the dunitic rocks and high forsterite contents (Mg# 91 to 92.5) of the olivines, all point to a layered cumulate origin for the Miaggoq body. Pseudosection calculations along with geothermometry estimations reveal peak metamorphic conditions of 850–1100 °C at pressures of 0.7–1.25 GPa under anhydrous conditions followed by a possible metamorphic overprint at 650–800 °C and 0.7 GPa with relatively dry melting (0.025–0.125 wt% H2O). MELTS fractional crystallization coupled with cumulate modelling approximated the compositional trends with conditions on ∼3 kbar with 1 wt% H2O. This research concludes that the Miaggoq body represents a layered cumulate complex that was derived by large degrees of partial melting of the mantle with possible assimilation (synonymous with contamination) of basalts in the crust. Overall, this study provides complementary data for the Mesoarchaean cumulate bodies of the Akia Terrane and their petrological processes.Peer reviewe
Exploiting sodium ascorbate as an underutilized and sustainable sacrificial reductant for net reductive pinacol coupling reactions via mechanophotocatalysis
Get PDFFunding: The authors thank the Leverhulme Trust (RPG-2023-110), the Engineering and Physical Sciences Research Council for funding (EP/W007517/1, EP/W015137/1, and EP/Z535291/1), and the European Commission (PhotoReAct ITN: 956324) for support. F. M. thanks the EaSI-CAT CDT at the University of St Andrews for support in the form of a studentship.Mechanochemistry can mediate reactions containing components that are poorly soluble in organic solvents, thereby facilitating access to new chemical space. These reagents may also be safer to handle and less costly than analogs used in solution-state reactions, providing secondary tangible benefits. In this study, we report the use of sodium ascorbate as a sacrificial reductant in net reductive pinacol couplings of aromatic aldehydes and ketones driven by mechanophotocatalysis. Sodium ascorbate replaces the sacrificial reductants typically used to deliver these 1,2-diol products (such as DIPEA and the Hantzsch ester). The solvent-minimized protocol returned more consistent results than the solution-state reference reaction, highlighting mechanophotocatalysis as a valuable tool for mediating heterogeneous photochemical reactions. An initial positive result for a reductive amination protocol using ascorbate is also disclosed.Peer reviewe
Climbing the hyperintensional mountain : an essay on impossible worlds, subject matters and truthmakers
Get PDFStarting with considerations on why one would want hyperintensional theories of content, this thesis engages in an exploration of three main strands in contemporary hyperintensional semantics and metaphysics: impossible worlds semantics, subject matter theory and truthmaker semantics. Its central claim is that the best hyperintensional theories for various purposes use important insights from these three ways of doing semantics. Starting with a space of possible worlds and expanding it, as Berto and Jago (2019) do, to a space of ‘open’ impossible worlds, we get too anarchic a space of worlds, however closing it under any logical consequence relation, like FDE, we idealize too much if our goal is to model realistic epistemic agents. Adding subject matters (Silva, 2024a) helps to find a happy middle ground. This leaves open the question of how to characterize subject matters, and here the notion of exact verification, I argue, helps in defining a new notion of what we may call `topical truthmaking' which in turn helps define the notion of a subject matter. Closing the circle, recently Berto and Jago (2023) have argued that truthmaker semantics and impossible worlds semantics are notational variants of one another, save for the former’s emphasis on exact verification. I myself argue for this equivalence (Silva, 2024c) by showing that the ontology presupposed by standard truthmaker semantics, as presented in (Fine, 2017a), is the same as the one employed by Berto and Jago (2019).
Having developed the aforementioned theoretical background in the first part of the thesis, I then apply the hyperintensional framework in the second part. Namely, I do so to: epistemic logic; the demarcation of the logical vocabulary; and transfeminist philosophy. Longer proofs were saved for a formal appendix
A mosaic of modular variation at a single gene underpins convergent plumage coloration
Get PDFFunding: This research was supported by German Research Foundation (DFG) research grant BU3456/3-1 and Swiss National Science Foundation (SNSF) grant 310030_207417 to R.B., National Research Fund (FNR) Luxembourg grant 14575729 to D.L., an A.G. Leventis Foundation Grant to A.N.G.K., a Georg Foster Research Stipend of the Alexander von Humboldt Foundation and a scholarship for female researchers from Friedrich-Schiller-University Jena to N.A.K., and a Swedish Research Council (Vetenskapsrådet) grant 2022-06195 to V.P.The reshuffling of genomic variation from multiple origins is an important contributor to phenotypic diversification, yet insights into the evolutionary trajectories of this combinatorial process and their interplay with genetic architecture remain scarce. We show that convergent plumage color evolution in wheatears involves a monogenic architecture with modular variation introgressed at the agouti signaling protein (ASIP) locus. Introgression of a new transposable element insertion and linked protein-coding variation underpin a transspecific throat color polymorphism, which stable isotopes suggest is associated with alternative foraging niches. Cointrogression of linked regulatory ASIP variation resulted in mantle color convergence in one species, whereas convergent color evolution at the genus level required new variation. Our results demonstrate evolutionary trajectories from introgressed variation realized within the constraints of a monogenic architecture.Peer reviewe
Intrinsic mechanisms contributing to the biophysical signature of mouse gamma motoneurons
Get PDFFunding: Canadian Institute for Health Research Grant Number(s): PDF - 202012MFE - 459188 - 297534; The Wellcome Trust Grant Number(s): ISSF - 204821/Z/16/Z; The Lundbeck Foundation Grant Number(s): R434-2023-347; Royal Society (Grant Number(s): NIF\R1\180091.Precise motor control relies on continuous sensory feedback from muscles, a process in which gamma motoneurons play a key role. These specialized spinal neurons innervate intrafusal muscle fibres, modulating their sensitivity to stretch and maintaining proprioceptive signalling during movement. Gamma motoneurons are characterized by a distinct biophysical profile, including low recruitment thresholds and high firing rates that enable rapid activation of intrafusal fibres at contraction onset. Despite their importance, the intrinsic mechanisms that underlie these properties remain poorly understood. In the present study, we analysed published and unpublished data to identify a population of low-threshold, high-gain motoneurons with features consistent with gamma motoneurons, emerging during the third postnatal week in mice. Their low recruitment threshold was linked to lower membrane capacitance, higher input resistance, a more hyperpolarized activation of persistent inward currents (PICs) and a narrower axon initial segment. By contrast, higher firing rates were associated not with PIC amplitude but with shorter action potential durations and smaller medium afterhyperpolarizations. Notably, 92% of putative gamma motoneurons exhibited a sodium pump-mediated ultra-slow afterhyperpolarization, which was absent in slow alpha motoneurons. This difference could not be attributed to h-current activity or expression of the alpha 3 subunit of the sodium-potassium ATPase. These findings reveal key intrinsic properties that support the unique excitability of gamma motoneurons, offering new insight into their contribution to motor control. This work provides a foundation for future studies into their development, regulation and involvement in neuromuscular disorders.Peer reviewe
From the margins to the core : implementing an inclusive academic community for empowered learning
Get PDFIn higher education (HE), academic development and in-sessional provision have traditionally existed at the margins, often treated as supplementary rather than integral to institutional priorities. However, as student demographics and academic demands evolve, the need for a more inclusive, integrated approach to student support becomes increasingly pressing. This reflective analysis explores the collaboration between two services situated within the third space (Whitchurch, 2008): academic skills provision offered by the Centre for Educational Enhancement and Development (CEED) and Academic English Services (AES) provided by the International Education Institute (IE). Through this partnership, we sought to challenge entrenched othering structures that distinguish international from home students and reinforce the problematic dichotomy between native and non-native English speakers. Drawing from practitioner-based enquiry, we outline the steps taken to integrate these services and develop a student-centred provision that fosters autonomy and inclusivity. Our approach intentionally moves beyond problematising existing labels, instead focusing on dismantling institutional barriers that have historically segregated academic and language support. By aligning pedagogical and operational strategies, we created a unified framework that allows all learners to access tailored support without being restricted by linguistic or institutional classifications. This reflective analysis critically examines the early stages of our collaboration, drawing from qualitative and quantitative data to evaluate its impact. We unpick the successes and challenges encountered in navigating institutional constraints, streamlining service provision, and fostering a more cohesive academic community. Our findings contribute to ongoing discussions on cross-departmental collaborations and provide a potential blueprint for integrating academic and language development within the third space. Ultimately, we advocate for a model that prioritises learner agency, challenges deficit-based perspectives, and repositions academic development as a core function within HE institutions.Peer reviewe
From deprivation to criminality : reversing the trend by harnessing the blue economy to tackle criminality at sea (CAS)
Get PDFAfrican oceans and the resources within them contribute to coastal livelihoods and the food security of millions of African people; at the same time, these same people are most vulnerable to the adverse effects of climate change, marine pollution, illegal, unreported and unregulated fishing, piracy and armed robbery at sea, expansion of the Blue Economy sector and the overall impact of depleting oceans resources and insecurity. Understanding how they respond to their vulnerabilities could be useful for addressing maritime security threats holistically and redirecting investments, allowing for the sustainable development of the Blue Economy in a way that adheres to the conceptual definition of the concept, encompassing the improvement of economic growth while ensuring social equity and environmental conservation. This agenda-setting transdisciplinary paper combines ideas from criminology, security and development fields to explore the nexus between deprivation in coastal communities in Africa and criminality at sea and how Africa’s Blue Economy can be leveraged to reverse the trend and ensure sustainable development ashore. Grounded in the critical review of the literature and the author’s theoretical and empirical insights into the Blue Economy, ocean governance and maritime security in Africa. The paper enhances our understanding of the interplay between deprivation and criminality at sea, and how sustainable Blue Economy and maritime security can reverse this trend.Peer reviewe
Global crises and utopian hope : an introduction
Get PDFAs humanity faces the prospect of imminent civilizational catastrophe, the aspirational sense that the future contains the potential for better ways of living and being appears to be fading under the strain of pervasive polycrisis. This special issue focuses on the question of whether it remains possible to reanimate critical utopian hope in the current climate of profound anxiety, pessimism, and dread over the multiple, intersecting global crises of our time. After first highlighting the dual crisis of hope and utopian ethical-political thinking today, it complicates conventional wisdom regarding hope and utopianism by showing that these notions are fundamentally shaped by experiences of disappointment, failure, and uncertainty. Utopian hope about the future, in other words, is not antithetical or irrelevant to the age of global polycrisis but precisely what should be occasioned by the stark realities of our times. From this standpoint, the introduction explains how the contributions to this special issue explore fragile, precarious yet realistic prospects for collective hope and, across a selection of concrete sociopolitical challenges, demonstrate that transformative changes still can be made to bring about the better futures we may imagine without being disconnected from the demand for pragmatism and the real prospect of failure.Peer reviewe
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