Characterisation of the LH2 complexes of Allochromatium vinosum

Purple photosynthetic bacteria contain a highly efficient light-harvesting system of LH2 and LH1 complexes, consisting of peptides, bacteriochlorophyll, and carotenoids, which allow cells to grow photosynthetically under different environmental conditions. Allochromatium (Alc.) vinosum is a sulphur purple photosynthetic bacterium that was found to produce several different LH2 complex types under different growth and nutritional conditions. These LH2 complexes have been identified as the B800-820, B800-840, and B800-850. All of the LH2 complex types of Alc. vinosum were confirmed as heterogeneous forming part of the basis of the unusual split B800 peak due to two potential B800 binding sites on the alpha peptides. This work produced CD data to suggest that excitonic coupling of the B800 BChl occurs and Monte Carlo simulations produced in conjunction with this work indicated that this would also contribute to the splitting of the band observed. The carotenoids of the spirilloxanthin pathway were identified within all of the LH2 complexes, however, the specific carotenoid composition varied depending on the LH2 complex type. Unlike most purple photosynthetic bacteria, Alc. vinosum is able to produce LH2 complexes in the absence of carotenoid biosynthesis. Carotenoidless LH complexes are ideal for the process of reconstitution, often used to elucidate structure function relationships within complexes. Carotenoidless LH2 complexes were produced and used for proof of concept reversible dissociation studies. This work identified the B800-850 LH2 complex as a reconstitution candidate for further work

Category is... Staff and student experiences of Rainbow Office Hours

In this paper we present staff and student experiences of "Rainbow Office Hours", a distinct, safe space for LGBTQ+ community engagement in higher education, challenging traditional professional identity boundaries and promoting visibility and representation. Originating at the University of Glasgow in 2019, students are invited to attend specific times labelled as Rainbow Office Hours with an LGBTQ+ member of staff to discuss anything LGBTQ+ related. This initiative has helped foster an inclusive campus climate, underscoring the need for broader institutional support for LGBTQ+ identities. We advocate for integrating queer perspectives across academic disciplines, emphasising the critical role of representation in educational environments and critiquing the prevailing heteronormative and cisnormative institutional cultures that discourage the integration of sexual and gender minority issues into academia. We cannot, and will not, leave who we are at the door when we arrive at work

Ultra-broadband 2D electronic spectroscopy of carotenoid-bacteriochlorophyll interactions in the LH1 complex of a purple bacterium

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Antenatal health promotion via short message service at a Midwife Obstetrics Unit in South Africa: a mixed methods study

Abstract Background Adequate antenatal care is important to both the health of a pregnant woman and her unborn baby. Given South Africa’s high rate of cellphone penetration, mobile health interventions have been touted as a potentially powerful means to disseminate health information. This study aimed to increase antenatal health knowledge and awareness by disseminating text messages about clinic procedures at antenatal visits, and how to be healthy during pregnancy. Methods Participants recruited were pregnant women attending a primary health care facility in Cape Town. A controlled clinical trial was carried out where the intervention group (n = 102) received text messages staggered according to the week of pregnancy at the time of recruitment. The control group (n = 104) received no text messages. These text messages contained antenatal health information, and were delivered in English, Xhosa or Afrikaans, according to the preference of each participant. A baseline knowledge questionnaire with nine questions was administered prior to the intervention. The same questionnaire was used with added health-related behaviour questions for the intervention group at exit. A modified intention-to-treat analysis was done. To compare the control and intervention group’s knowledge, Fisher’s exact tests and two-sample t-tests tests were carried out for binary and continuous outcomes, respectively. A focus group of seven participants from the intervention group was then conducted to gain more insight into how the text messages were perceived. Results There was substantial loss to follow-up during the study with only 57% of the participants retained at exit. No statistically significant difference was detected between the control and intervention group in any of the nine knowledge questions at exit (all p > 0.05). Responses from the focus group indicated that the text messages acted as a welcome reminder and a source of positive motivation, and were perceived as extended care from the health care provider. Conclusions While the intervention failed to improve antenatal health knowledge, evidence from self-reported behaviour and the focus group suggests that text messages have the potential to motivate change in health-seeking behaviour. One should be mindful of loss to follow-up when rolling out mobile health interventions in developing country settings. Trial registration Pan African Clinical Trials Registry PACTR201406000841188 . Registered 3 June 2014

Levetiracetam versus phenytoin for second-line treatment of paediatric convulsive status epilepticus (EcLiPSE): a multicentre, open-label, randomised trial

Background Phenytoin is the recommended second-line intravenous anticonvulsant for treatment of paediatric convulsive status epilepticus in the UK; however, some evidence suggests that levetiracetam could be an effective and safer alternative. This trial compared the efficacy and safety of phenytoin and levetiracetam for second-line management of paediatric convulsive status epilepticus.Methods This open-label, randomised clinical trial was undertaken at 30 UK emergency departments at secondary and tertiary care centres. Participants aged 6 months to under 18 years, with convulsive status epilepticus requiring second-line treatment, were randomly assigned (1:1) using a computer-generated randomisation schedule to receive levetiracetam (40 mg/kg over 5 min) or phenytoin (20 mg/kg over at least 20 min), stratified by centre. The primary outcome was time from randomisation to cessation of convulsive status epilepticus, analysed in the modified intention-to-treat population (excluding those who did not require second-line treatment after randomisation and those who did not provide consent). This trial is registered with ISRCTN, number ISRCTN22567894.Findings Between July 17, 2015, and April 7, 2018, 1432 patients were assessed for eligibility. After exclusion of ineligible patients, 404 patients were randomly assigned. After exclusion of those who did not require second-line treatment and those who did not consent, 286 randomised participants were treated and had available data: 152 allocated to levetiracetam, and 134 to phenytoin. Convulsive status epilepticus was terminated in 106 (70%) children in the levetiracetam group and in 86 (64%) in the phenytoin group. Median time from randomisation to cessation of convulsive status epilepticus was 35 min (IQR 20 to not assessable) in the levetiracetam group and 45 min (24 to not assessable) in the phenytoin group (hazard ratio 1·20, 95% CI 0·91–1·60; p=0·20). One participant who received levetiracetam followed by phenytoin died as a result of catastrophic cerebral oedema unrelated to either treatment. One participant who received phenytoin had serious adverse reactions related to study treatment (hypotension considered to be immediately life-threatening [a serious adverse reaction] and increased focal seizures and decreased consciousness considered to be medically significant [a suspected unexpected serious adverse reaction]). Interpretation Although levetiracetam was not significantly superior to phenytoin, the results, together with previously reported safety profiles and comparative ease of administration of levetiracetam, suggest it could be an appropriate alternative to phenytoin as the first-choice, second-line anticonvulsant in the treatment of paediatric convulsive status epilepticus

On light-induced photoconversion of B800 bacteriochlorophylls in the LH2 antenna of the purple sulfur bacterium Allochromatium vinosum

The B800-850 LH2 antenna from the photosynthetic purple sulfur bacterium Allochromatium vinosum exhibits an unusual spectral splitting of the B800 absorption band; i.e., two bands are well-resolved at 5 K with maxima at 805 nm (B800R) and 792 nm (B800B). To provide more insight into the nature of the B800 bacteriochlorophyll (BChl) a molecules, high-resolution hole-burning (HB) spectroscopy is employed. Both white light illumination and selective laser excitations into B800R or B800B lead to B800R → B800B phototransformation. Selective excitation into B800B leads to uncorrelated excitation energy transfer (EET) to B800R and subsequent B800R → B800B phototransformation. The B800B → B800R EET time is 0.9 ± 0.1 ps. Excitation at 808.4 nm (into the low-energy side of B800R) shows that the lower limit of B800R → B850 EET is about 2 ps, as the B800R → B800B phototransformation process could contribute to the corresponding zero-phonon hole width. The phototransformation of B800R leads to a ∼ 200 cm–1 average blue-shift of transition energies, i.e., B800R changes into B800B. We argue that it is unlikely that B800-B850 excitonic interactions give rise to a splitting of the B800 band. We propose that the latter is caused by different protein conformations that can lead to both strong or weak hydrogen bond(s) between B800 pigments and the protein scaffolding. Temperature-dependent absorption spectra of B800, which revealed a well-defined isosbestic point, support a two-site model, likely with strongly and weakly hydrogen-bonded B800 BChls. Thus, BChls contributing to B800R and B800B could differ in the position of the proton in the BChl carbonyl-protein hydrogen bond, i.e., proton dynamics along the hydrogen bond may well be the major mechanism of this phototransformation. However, the effective tunneling mass is likely larger than the proton mass

The origin of the split B800 absorption peak in the LH2 complexes from Allochromatium vinosum

The absorption spectrum of the high-light peripheral light-harvesting (LH) complex from the photosynthetic purple bacterium Allochromatium vinosum features two strong absorptions around 800 and 850 nm. For the LH2 complexes from the species Rhodopseudomonas acidophila and Rhodospirillum molischianum, where high-resolution X-ray structures are available, similar bands have been observed and were assigned to two pigment pools of BChl a molecules that are arranged in two concentric rings (B800 and B850) with nine (acidophila) or eight (molischianum) repeat units, respectively. However, for the high-light peripheral LH complex from Alc. vinosum, the intruiging feature is that the B800 band is split into two components. We have studied this pigment–protein complex by ensemble CD spectroscopy and polarisation-resolved single-molecule spectroscopy. Assuming that the high-light peripheral LH complex in Alc. vinosum is constructed on the same modular principle as described for LH2 from Rps. acidophila and Rsp. molischianum, we used those repeat units as a starting point for simulating the spectra. We find the best agreement between simulation and experiment for a ring-like oligomer of 12 repeat units, where the mutual arrangement of the B800 and B850 rings resembles those from Rsp. molischianum. The splitting of the B800 band can be reproduced if both an excitonic coupling between dimers of B800 molecules and their interaction with the B850 manifold are taken into account. Such dimers predict an interesting apoprotein organisation as discussed below

Elementary Energy Transfer Pathways in Allochromatium vinosum Photosynthetic Membranes

AbstractAllochromatium vinosum (formerly Chromatium vinosum) purple bacteria are known to adapt their light-harvesting strategy during growth according to environmental factors such as temperature and average light intensity. Under low light illumination or low ambient temperature conditions, most of the LH2 complexes in the photosynthetic membranes form a B820 exciton with reduced spectral overlap with LH1. To elucidate the reason for this light and temperature adaptation of the LH2 electronic structure, we performed broadband femtosecond transient absorption spectroscopy as a function of excitation wavelength in A. vinosum membranes. A target analysis of the acquired data yielded individual rate constants for all relevant elementary energy transfer (ET) processes. We found that the ET dynamics in high-light-grown membranes was well described by a homogeneous model, with forward and backward rate constants independent of the pump wavelength. Thus, the overall B800→B850→B890→ Reaction Center ET cascade is well described by simple triexponential kinetics. In the low-light-grown membranes, we found that the elementary backward transfer rate constant from B890 to B820 was strongly reduced compared with the corresponding constant from B890 to B850 in high-light-grown samples. The ET dynamics of low-light-grown membranes was strongly dependent on the pump wavelength, clearly showing that the excitation memory is not lost throughout the exciton lifetime. The observed pump energy dependence of the forward and backward ET rate constants suggests exciton diffusion via B850→ B850 transfer steps, making the overall ET dynamics nonexponential. Our results show that disorder plays a crucial role in our understanding of low-light adaptation in A. vinosum

Conformational Complexity in the LH2 Antenna of the Purple Sulfur Bacterium <i>Allochromatium vinosum</i> Revealed by Hole-Burning Spectroscopy

This work discusses the protein conformational complexity of the B800–850 LH2 complexes from the purple sulfur bacterium <i>Allochromatium vinosum</i>, focusing on the spectral characteristics of the B850 chromophores. Low-temperature B850 absorption and the split B800 band shift blue and red, respectively, at elevated temperatures, revealing isosbestic points. The latter indicates the presence of two (unresolved) conformations of B850 bacteriochlorophylls (BChls), referred to as conformations 1 and 2, and two conformations of B800 BChls, denoted as B800_R and B800_B. The energy differences between average site energies of conformations 1 and 2, and B800_R and B800_B are similar (∼200 cm^–1), suggesting weak and strong hydrogen bonds linking two major subpopulations of BChls and the protein scaffolding. Although conformations 1 and 2 of the B850 chromophores, and B800_R and B800_B, exist in the ground state, selective excitation leads to 1 → 2 and B800_R → B800_B phototransformations. Different static inhomogeneous broadening is revealed for the lowest energy exciton states of B850 (fwhm ∼195 cm^–1) and B800_R (fwhm ∼140 cm^–1). To describe the 5 K absorption spectrum and the above-mentioned conformations, we employ an exciton model with dichotomous protein conformation disorder. We show that both experimental data and the modeling study support a two-site model with strongly and weakly hydrogen-bonded B850 and B800 BChls, which under illumination undergo conformational changes, most likely caused by proton dynamics