Proteins containing photosynthetic reaction centre domains modulate FtsZ-based archaeal cell division.

Cell division in all domains of life requires the orchestration of many proteins, but in Archaea most of the machinery remains poorly characterized. Here we investigate the FtsZ-based cell division mechanism in Haloferax volcanii and find proteins containing photosynthetic reaction centre (PRC) barrel domains that play an essential role in archaeal cell division. We rename these proteins cell division protein B 1 (CdpB1) and CdpB2. Depletions and deletions in their respective genes cause severe cell division defects, generating drastically enlarged cells. Fluorescence microscopy of tagged FtsZ1, FtsZ2 and SepF in CdpB1 and CdpB2 mutant strains revealed an unusually disordered divisome that is not organized into a distinct ring-like structure. Biochemical analysis shows that SepF forms a tripartite complex with CdpB1/2 and crystal structures suggest that these two proteins might form filaments, possibly aligning SepF and the FtsZ2 ring during cell division. Overall our results indicate that PRC-domain proteins play essential roles in FtsZ-based cell division in Archaea.

The UVA response of enolic dibenzoylmethane: beyond the static approach.

Enolic dibenzoylmethane is used in cosmetic sunscreens as a UVA filter because it strongly absorbs radiation around 340 nm. Assessing the absorption properties solely on the basis of the vertical excitation spectrum at the minimum of the potential energy surface leads to the conclusion that the nπ* state is not initially photoexcited. Since this molecule exhibits large changes in structure due to nuclear thermal and quantum fluctuations, it is not sufficient to consider one molecular configuration but an ensemble of configurations. In this work, we simulate its UVA response by employing the DFT/MRCI method in conjunction with configurations sampled from density functional theory-based classical and path integral molecular dynamics as well as by computing Franck-Condon factors. Our findings indicate that thermal and nuclear quantum fluctuations symmetrically broaden the excited states' absorption within the semi-classical approximation and thus it is necessary to include vibronic effects in order to correctly reproduce the experimental spectrum. The absorption is largely dominated by the ππ* state but there is a minor contribution from the nπ* state, contrary to the static result. The crossing between these two states occurs during the intramolecular proton transfer. This knowledge is of importance for studying photorelaxation mechanisms of dibenzoylmethane and other ß-diketone compounds.

New Insight into Uracil Stacking in Water from ab Initio Molecular Dynamics.

Nucleobases spontaneously aggregate in water by forming stacked dimers and multimers. It is assumed that the main contributions to the aggregation stem from hydrophobic and base-base dispersion interactions. By studying the uracil monomer and dimer in bulk water with the first principle molecular dynamics, we discuss dimer structure and provide evidence that stacking increases the uracil-water hydrogen bonding strength and alters the hydration structure of uracil. These changes have a significant influence on the intensity and shift of the carbonyl stretching band as revealed by simulated infrared absorption spectra of the monomer and dimer and available experimental spectra. The contributions of dipole-dipole, dispersion, and water mediated forces to the stacking are discussed. The reported findings are valuable for understanding the microscopic mechanism of heteroaromatic association in water which is relevant to a large range of chemical and biological systems.

The effect of short-term treatment with lithium carbonate on the outcome of radioiodine therapy in patients with long-lasting Graves' hyperthyroidism.

OBJECTIVE: The outcome of radioiodine therapy (RIT) in Graves' hyperthyroidism (GH) mainly depends on radioiodine (131I) uptake and the effective half-life of 131I in the gland. Studies have shown that lithium carbonate (LiCO3) enhances the 131I half-life and increases the applied thyroid radiation dose without affecting the thyroid 131I uptake. We investigated the effect of short-term treatment with LiCO3 on the outcome of RIT in patients with long-lasting GH, its influence on the thyroid hormones levels 7 days after RIT, and possible side effects. METHODS: Study prospectively included 30 patients treated with LiCO3 and 131I (RI-Li group) and 30 patients only with 131I (RI group). Treatment with LiCO3 (900 mg/day) started 1 day before RIT and continued 6 days after. Anti-thyroid drugs withdrawal was 7 days before RIT. Patients were followed up for 12 months. We defined a success of RIT as euthyroidism or hypothyroidism, and a failure as persistent hyperthyroidism. RESULTS: In RI-Li group, a serum level of Li was 0.571 ± 0.156 mmol/l before RIT. Serum levels of TT4 and FT4 increased while TSH decreased only in RI group 7 days after RIT. No toxic effects were noticed during LiCO3 treatment. After 12 months, a success of RIT was 73.3% in RI and 90.0% in RI-Li group (P < 0.01). Hypothyroidism was achieved faster in RI-Li (1st month) than in RI group (3rd month). Euthyroidism slowly decreased in RI-Li group, and not all patients became hypothyroid for 12 months. In contrast, euthyroidism rapidly declined in RI group, and all cured patients became hypothyroid after 6 months. CONCLUSION: The short-term treatment with LiCO3 as an adjunct to 131I improves efficacy of RIT in patients with long-lasting GH. A success of RIT achieves faster in lithium-treated than in RI group. Treatment with LiCO3 for 7 days prevents transient worsening of hyperthyroidism after RIT. Short-term use of LiCO3 shows no toxic side effects.

A new insight into the photochemistry of avobenzone in gas phase and acetonitrile from ab initio calculations.

Avobenzone (4-tert-butyl-4'-methoxydibenzoylmethane, AB) is one of the most widely used filters in sunscreens for skin photoprotection in the UVA band. The photochemistry of AB includes keto-enol tautomerization, cis-trans isomerization, rotation about the single bond and α bond cleavages of carbonyl groups. In this contribution we study chelated and non-chelated enol, rotamers Z and E, and keto tautomers of AB in the ground and excited states in gas phase and acetonitrile by means of a coupled cluster method. Our findings suggest that torsion around the double C2-C3 bond of photoexcited chelated enol leads to internal conversion to the ground state and formation of rotamer E. In addition, opening of the chelated hydrogen ring by torsion of the hydroxyl group creates non-chelated enol. The possible mechanisms of rotamer Z formation are discussed. The solvent dependent photolability is related to the relative order of the lowest triplet ππ* and nπ* states of the keto tautomer.

Short term treatment with lithium carbonate as adjunct to radioiodine treatment for long-lasting Graves' hyperthyroidism.

OBJECTIVE: Lithium carbonate is primarily used for the treatment of patients with bipolar affective disorders. Initial treatment of Graves' hyperthyroidism (GHT) with antithyroid drugs (ATD) has limitations at over 50% of treated patients because of significant side effects and relatively high relapses of the disease after drugs withdrawal. Till now, the influence of LiCO3on RIT outcome was mainly studied in patients with recent onset of GHT, and results were contradicted. Meta-analysis of case-control studies showed higher rated hypothyroidism in patients with mood disorders treated with LiCO3(121/869) than in controls (10/578). Although in a small number of patients (n=28) with long-lasting GHT, preliminary results of ours showed that ¹³¹I treatment with LiCO3for 7 days significantly improved the efficacy of RIT versus the non-LiCO3treated patients (P<0.001). Lithium treated patients were cured faster (12 of 13 patients were cured after one month) than those treated only with ¹³¹I (8 patients were cured after one and 11/15 patients after 12 months). Fewer patients treated with ¹³¹I and LiCO3had persistent hyperthyroidism than those treated with ¹³¹I alone. There were no toxic effects of LiCO3during 7 days treatment. CONCLUSION: These observations indicate of that short-term treatment with LiCO3in GHT patients as adjunct to ¹³¹I-NaI improves the efficacy of RIT, prevents transient exacerbation of hyperthyroidism, early induction of hypothyroidism and does not worsen ophthalmopathy.