Role of tyrosine M210 in the initial charge separation of reaction centers of Rhodobacter sphaeroides

Femtosecond spectroscopy was used in combination with site-directed mutagenesis to study the influence of tyrosine M210 (YM210) on the primary electron transfer in the reaction center of Rhodobacter sphaeroides. The exchange of YM210 to phenylalanine caused the time constant of primary electron transfer to increase from 3.5 f 0.4 ps to 16 f 6 ps while the exchange to leucine increased the time constant even more to 22 f 8 ps. The results suggest that tyrosine M210 is important for the fast rate of the primary electron transfer

First step to eradication of Poa annua L. from Point Thomas Oasis (King George Island, South Shetlands, Antarctica)

Poa annua, an alien species reported from the Antarctic continent and many Antarctic and sub-Antarctic islands, was accidentally introduced in the vicinity of the Polish Antarctic Station H. Arctowski. Recently the species has been found entering native plant communities. In almost 30 years it dispersed over 250 m from the site it was first observed and can therefore be considered invasive. We report the first steps to eradicate the species following the initial research to quantify the biology, ecology and genetics of the species. After detailed mapping of all 1439 tussocks located in the Arctowski Station area we removed 314 tussocks closest to a moss carpet formation (native plant community of high conservation value). All of the 49 tussocks growing in the Ecology Glacier forefield were removed. It is the biggest alien plant eradication act conducted so far in Antarctica. We plan to continue the eradication process and monitor the eradicated sites. This will provide valuable information on impacts and issuesrelated to removal of alien species in the maritime Antarctic and will help in informing future decisions on management of other plant invasions in the region. Given the increasing human traffic to the Antarctic and the associated risks of invasion our results will be important not only for Arctowski but also for the whole Antarctic region

Structural and spectropotentiometric analysis of Blastochloris viridis heterodimer mutant reaction center

Heterodimer mutant reaction centers (RCs) of Blastochloris viridis were crystallized using microfluidic technology. In this mutant, a leucine residue replaced the histidine residue which had acted as a fifth ligand to the bacteriochlorophyll (BChl) of the primary electron donor dimer M site (HisM200). With the loss of the histidine-coordinated Mg, one bacteriochlorophyll of the special pair was converted into a bacteriopheophytin (BPhe), and the primary donor became a heterodimer supermolecule. The crystals had dimensions 400 × 100 ×100 μm, belonged to space group P43212, and were isomorphous to the ones reported earlier for the wild type (WT) strain. The structure was solved to a 2.5 Å resolution limit. Electron-density maps confirmed the replacement of the histidine residue and the absence of Mg. Structural changes in the heterodimer mutant RC relative to the WT included the absence of the water molecule that is typically positioned between the M side of the primary donor and the accessory BChl, a slight shift in the position of amino acids surrounding the site of the mutation, and the rotation of the M194 phenylalanine. The cytochrome subunit was anchored similarly as in the WT and had no detectable changes in its overall position. The highly conserved tyrosine L162, located between the primary donor and the highest potential heme C380, revealed only a minor deviation of its hydroxyl group. Concomitantly to modification of the BChl molecule, the redox potential of the heterodimer primary donor increased relative to that of the WT organism (772 mV vs. 517 mV). The availability of this heterodimer mutant and its crystal structure provides opportunities for investigating changes in light-induced electron transfer that reflect differences in redox cascades

Weak temperature dependence of P (+) H A (-) recombination in mutant Rhodobacter sphaeroides reaction centers

International audienceIn contrast with findings on the wild-type Rhodobacter sphaeroides reaction center, biexponential P (+) H A (-) → PH A charge recombination is shown to be weakly dependent on temperature between 78 and 298 K in three variants with single amino acids exchanged in the vicinity of primary electron acceptors. These mutated reaction centers have diverse overall kinetics of charge recombination, spanning an average lifetime from ~2 to ~20 ns. Despite these differences a protein relaxation model applied previously to wild-type reaction centers was successfully used to relate the observed kinetics to the temporal evolution of the free energy level of the state P (+) H A (-) relative to P (+) B A (-) . We conclude that the observed variety in the kinetics of charge recombination, together with their weak temperature dependence, is caused by a combination of factors that are each affected to a different extent by the point mutations in a particular mutant complex. These are as follows: (1) the initial free energy gap between the states P (+) B A (-) and P (+) H A (-) , (2) the intrinsic rate of P (+) B A (-) → PB A charge recombination, and (3) the rate of protein relaxation in response to the appearance of the charge separated states. In the case of a mutant which displays rapid P (+) H A (-) recombination (ELL), most of this recombination occurs in an unrelaxed protein in which P (+) B A (-) and P (+) H A (-) are almost isoenergetic. In contrast, in a mutant in which P (+) H A (-) recombination is relatively slow (GML), most of the recombination occurs in a relaxed protein in which P (+) H A (-) is much lower in energy than P (+) H A (-) . The weak temperature dependence in the ELL reaction center and a YLH mutant was modeled in two ways: (1) by assuming that the initial P (+) B A (-) and P (+) H A (-) states in an unrelaxed protein are isoenergetic, whereas the final free energy gap between these states following the protein relaxation is large (~250 meV or more), independent of temperature and (2) by assuming that the initial and final free energy gaps between P (+) B A (-) and P (+) H A (-) are moderate and temperature dependent. In the case of the GML mutant, it was concluded that the free energy gap between P (+) B A (-) and P (+) H A (-) is large at all times

Quality of treatment and surgical approach for rectal gastrointestinal stromal tumour (GIST) in a large European cohort

Background: Rectal gastrointestinal stromal tumours (GISTs) are rare tumours. Variability in the managementmay influence outcome, but there is a lack of understanding regarding contemporary variancein care. A multicenter, international, retrospective cohort study was performed to elucidate characteristicsand outcomes of rectal GIST in European practice, with particular reference to surgical approach.Methods: All rectal GIST patients diagnosed between 2009 and 2018 were identified from five Europeandatabases. Recurrence free survival (RFS) and overall survival (OS) were estimated using Kaplan-Meiermethod. Possible confounders were identified using Cox regression analyses.Results: From 210 patients, 155 patients had surgery. The three main types of surgery were local tumourresection (LTR, n ¼ 46), low anterior resection (LAR, n ¼ 31) and abdomino-perineal resection (APR,n ¼ 32). Most patients received neoadjuvant (65%) and/or adjuvant imatinib therapy (66%). Localrecurrence rate after surgery was 15% and overall recurrence rate 28%. No significant differences werefound in terms of RFS nor OS between LTR, LAR and APR. However, locally resected tumours weresmaller, while LAR and APR patients more often received perioperative imatinib. General hospitalstreated smaller GISTs, offered imatinib less frequently, and had a higher tumour rupture rate. In the multivariate analysis in the group having LTR, APR or LAR, the only significant prognostic factor for localrecurrence was higher age (HR 1.06, CI 1.00e1.12, p ¼ 0.048).Conclusions: In European clinical practice for rectal GIST, LTR, LAR and APR have comparable localcontrol. Multimodal approach is higher and tumour rupture less frequent in specialist centres comparedto general hospitals.Experimentele farmacotherapi