High-resolution cryo-EM structure of photosystem II reveals damage from high-dose electron beams

Photosystem II (PSII) plays a key role in water-splitting and oxygen evolution. X-ray crystallography has revealed its atomic structure and some intermediate structures. However, these structures are in the crystalline state and its final state structure has not been solved. Here we analyzed the structure of PSII in solution at 1.95 Å resolution by single-particle cryo-electron microscopy (cryo-EM). The structure obtained is similar to the crystal structure, but a PsbY subunit was visible in the cryo-EM structure, indicating that it represents its physiological state more closely. Electron beam damage was observed at a high-dose in the regions that were easily affected by redox states, and reducing the beam dosage by reducing frames from 50 to 2 yielded a similar resolution but reduced the damage remarkably. This study will serve as a good indicator for determining damage-free cryo-EM structures of not only PSII but also all biological samples, especially redox-active metalloproteins

Accelerator based epithermal neutron source for clinical boron neutron capture therapy

The world’s first accelerator based epithermal neutron source for clinical boron neutron capture therapy (BNCT) was designed, developed, and commissioned between 2008 and 2010 by Sumitomo Heavy Industries in collaboration with Kyoto University at the Kyoto University Institute for Integrated Radiation and Nuclear Science. The accelerator system is cyclotron-based and accelerates a proton up to an energy of approximately 30 MeV. The proton strikes a beryllium target, which produces fast neutrons that traverse a beam shaping assembly composed of a combination of lead, iron, aluminum, and calcium fluoride to reduce the neutron energy down to the epithermal range (∼10 keV) suitable for BNCT. The system is designed to produce an epithermal neutron flux of up to 1.4 × 10 9 n · cm − 2 · s − 1 (exiting from the moderator of a 12 cm diameter collimator) with a proton current of 1 mA. In 2017, the same type of accelerator was installed at the Kansai BNCT Medical Center and in March 2020 the system received medical device approval in Japan (Sumitomo Heavy Industries, NeuCure® BNCT system). Soon after, BNCT for unresectable, locally advanced, and recurrent carcinoma of the head and neck region was approved by the Japanese government for reimbursement covered by the national health insurance system

Is Presence or History of Extracolonic Primary Malignancy a Risk for Colorectal Neoplasia? An Analysis of Patients Who Underwent Colonoscopy

Whether presence or history of extracolonic primary malignancy is a risk for colorectal neoplasia is not fully known. In this study, 26,452 first-time colonoscopy cases were examined using a colonoscopy database. Among the analyzed subjects, 3,026 (11%) subjects had history or concomitance of extracolonic primary malignancy, while the remaining 23,426 subjects did not. Colorectal neoplasia was observed in 39% of all the subjects. A crude comparison showed that the prevalence of any type of colorectal neoplasia was higher in subjects with extracolonic malignancy than in those without (42% vs. 39%, p＝0.0012). However, after adjusting for confounding factors, the odds ratios (ORs) of subjects with extracolonic malignancy for having colorectal neoplasia, advanced neoplasia, and cancer were all less than 1.0, and all significantly different from those of subjects without extracolonic malignancy. Analysis according to the type of extracolonic malignancy revealed that gastric cancer cases had a significantly lower risk for colorectal advanced neoplasia (OR:0.81;95% CI:0.67-0.99). Among major malignancies, only esophageal squamous cell cancer cases had increased risk for colorectal neoplasia (OR:1.66;95% CI:1.20-2.29). Patients with presence or history of extracolonic malignancy did not carry a higher risk of occurrence of colorectal neoplasia

Improvement in the neutron beam collimation for application in boron neutron capture therapy of the head and neck region

In June 2020, the Japanese government approved boron neutron capture therapy for the treatment of head and neck cancer. The treatment is usually performed in a single fraction, with the neutron irradiation time being approximately 30–60 min. As neutrons scatter in air and loses its intensity, it is preferable to bring the patient as close to the beam port as possible to shorten the irradiation time. However, this can be a challenge, especially for patients with head and neck cancer, as the shoulders are an obstacle to a clean positioning. In this study, a novel neutron collimation system for an accelerator based neutron source was designed to allow for a more comfortable treatment, without compromising the irradiation time. Experimental measurements confirmed the simulation results and showed the new collimator can reduce the irradiation time by approximately 60% (under the same condition where the distance between the source and the patient surface was kept the same). The dose delivered to the surrounding healthy tissue was reduced with the new collimator, showing a 25% decrease in the D₅₀ of the mucosal membrane. Overall, the use of the newly designed collimator will allow for a more comfortable treatment of the head and neck region, reduce the treatment time, and reduce the dose delivered to the surrounding healthy tissue

Structure of a tetrameric photosystem I from a glaucophyte alga Cyanophora paradoxa

Photosystem I (PSI) is one of the two photosystems functioning in light-energy harvesting, transfer, and electron transfer in photosynthesis. However, the oligomerization state of PSI is variable among photosynthetic organisms. We present a 3.8-angstrom resolution cryo-electron microscopic structure of tetrameric PSI isolated from the glaucophyte alga Cyanophora paradoxa, which reveals differences with PSI from other organisms in subunit composition and organization. The PSI tetramer is organized in a dimer of dimers with a C2 symmetry. Unlike cyanobacterial PSI tetramers, two of the four monomers are rotated around 90 degrees, resulting in a completely different pattern of monomer-monomer interactions. Excitation-energy transfer among chlorophylls differs significantly between Cyanophora and cyanobacterial PSI tetramers. These structural and spectroscopic features reveal characteristic interactions and excitation-energy transfer in the Cyanophora PSI tetramer, suggesting that the Cyanophora PSI could represent a turning point in the evolution of PSI from prokaryotes to eukaryotes

Structure of a cyanobacterial photosystem I surrounded by octadecameric IsiA antenna proteins

Iron-stress induced protein A (IsiA) is a chlorophyll-binding membrane-spanning protein in photosynthetic prokaryote cyanobacteria, and is associated with photosystem I (PSI) trimer cores, but its structural and functional significance in light harvesting remains unclear. Here we report a 2.7-angstrom resolution cryo-electron microscopic structure of a supercomplex between PSI core trimer and IsiA from a thermophilic cyanobacterium Thermosynechococcus vulcanus. The structure showed that 18 IsiA subunits form a closed ring surrounding a PSI trimer core. Detailed arrangement of pigments within the supercomplex, as well as molecular interactions between PSI and IsiA and among IsiAs, were resolved. Time-resolved fluorescence spectra of the PSI-IsiA supercomplex showed clear excitation-energy transfer from IsiA to PSI, strongly indicating that IsiA functions as an energy donor, but not an energy quencher, in the supercomplex. These structural and spectroscopic findings provide important insights into the excitation-energy-transfer and subunit assembly mechanisms in the PSI-IsiA supercomplex. Akita et al. present the latest approach to solve IsiA-PSI supercomplex molecular structure with increased resolution using cryo-EM and time-resolved fluorescence studies. With 2.7 angstrom resolution, they reveal molecular interactions between PSI and IsiA subunits and that IsiA functions as an energy donor in the supercomplex

Structural basis for different types of hetero-tetrameric light-harvesting complexes in a diatom PSII-FCPII supercomplex

Fucoxanthin chlorophyll (Chl) a/c-binding proteins (FCPs) function as light harvesters in diatoms. The structure of a diatom photosystem II-FCPII (PSII-FCPII) supercomplex have been solved by cryo-electron microscopy (cryo-EM) previously; however, the FCPII subunits that constitute the FCPII tetramers and monomers are not identified individually due to their low resolutions. Here, we report a 2.5 angstrom resolution structure of the PSII-FCPII supercomplex using cryo-EM. Two types of tetrameric FCPs, S-tetramer, and M-tetramer, are identified as different types of hetero-tetrameric complexes. In addition, three FCP monomers, m1, m2, and m3, are assigned to different gene products of FCP. The present structure also identifies the positions of most Chls c and diadinoxanthins, which form a complicated pigment network. Excitation-energy transfer from FCPII to PSII is revealed by time-resolved fluorescence spectroscopy. These structural and spectroscopic findings provide insights into an assembly model of FCPII and its excitation-energy transfer and quenching processes. Fucoxanthin chlorophyll a/c-binding proteins (FCPs) harvest light energy in diatoms. The authors analyzed a structure of PSII-FCPII supercomplex at high resolution by cryo-EM, which identified each FCP subunit and pigment network in the supercomplex

Structural basis for the adaptation and function of chlorophyll f in photosystem I

Chlorophylls (Chl) play pivotal roles in energy capture, transfer and charge separation in photosynthesis. Among Chls functioning in oxygenic photosynthesis, Chl f is the most red-shifted type first found in a cyanobacterium Halomicronema hongdechloris. The location and function of Chl f in photosystems are not clear. Here we analyzed the high-resolution structures of photosystem I (PSI) core from H. hongdechloris grown under white or far-red light by cryo-electron microscopy. The structure showed that, far-red PSI binds 83 Chl a and 7 Chl f, and Chl f are associated at the periphery of PSI but not in the electron transfer chain. The appearance of Chl f is well correlated with the expression of PSI genes induced under far-red light. These results indicate that Chl f functions to harvest the far-red light and enhance uphill energy transfer, and changes in the gene sequences are essential for the binding of Chl f

ギョウセイ ニ ヨル チイキ ネコカツドウ ノ シエン ジョウキョウ オヨビ ソノ コウカ ニツイテ

ノラ猫問題を解決する一つの対策として地域猫活動が各地で行われており,一部の行政でその活動を支援している。そこで,その支援状況とその効果を検討するために,全国の自治体を対象として調査用紙を配布し,2008年度における情報を収集した。その結果,東京都特別区で地域猫活動を支援する行政が多く認められた。また,政令指定都市,中核市および都道府県のいずれの行政でも地域猫活動の地域がないと回答したところが多かった。条例や制度,避妊去勢手術費の補助,講習会開催等の支援措置は,東京都特別区および東京都市部で多く,中核市および都道府県では少ない状況であった。今回の調査では地域猫活動を行政が支援することが,猫に関する苦情の減少,猫の処分数の減少,また住民間の親密の増加等に対して有効であるかどうかについては明らかにならなかったものの,行政機関がノラ猫対策を早めにとることや,その支援を積極的に行うことなどが,猫の処分数を減らすのに有効である可能性が示唆された。Activities by community volunteers who care for stray cats, such as neutering and caring for stray cats, were supported at various administrative levels in Japan. In order to identify the status of the activities in which support is provided by the administrations and to assess the effect, we conducted a questionnaire survey to each government in 2008. The activities to support volunteer activities related to stray cats was significantly higher in the 23 wards of Tokyo than in other cities in Tokyo. Many of the local administrations did not have information about whether there were any such activities. There were significantly more administrations in the 23 wards of Tokyo and the other cities in Tokyo than in local administrations, which supported the activities such as enacting ordinances and animal protection promotion plans, and providing financial assistance to cover the cost of sterilization surgeries. This study could not clarify the effects of these support activities on reducing the number of and the nuisances caused by stray cats. However, it was suggested that efforts at the early period by every administration to assess the situation of stray cats and offer support activities would make the animal protection plans more effective