Structural dissection of two redox proteins from the shipworm symbiont Teredinibacter turnerae.

The discovery of lytic polysaccharide monooxygenases (LPMOs), a family of copper-dependent enzymes that play a major role in polysaccharide degradation, has revealed the importance of oxidoreductases in the biological utilization of biomass. In fungi, a range of redox proteins have been implicated as working in harness with LPMOs to bring about polysaccharide oxidation. In bacteria, less is known about the interplay between redox proteins and LPMOs, or how the interaction between the two contributes to polysaccharide degradation. We therefore set out to characterize two previously unstudied proteins from the shipworm symbiont Teredinibacter turnerae that were initially identified by the presence of carbohydrate binding domains appended to uncharacterized domains with probable redox functions. Here, X-ray crystal structures of several domains from these proteins are presented together with initial efforts to characterize their functions. The analysis suggests that the target proteins are unlikely to function as LPMO electron donors, raising new questions as to the potential redox functions that these large extracellular multi-haem-containing c-type cytochromes may perform in these bacteria.

CHARIOT: a phase I study of berzosertib with chemoradiotherapy in oesophageal and other solid cancers using time to event continual reassessment method.

BACKGROUND: Berzosertib (M6620) is a highly potent (IC50 = 19 nM) and selective, first-in-class ataxia telangiectasia-mutated and Rad3-related protein kinase (ATR) inhibitor. This trial assessed the safety, preliminary efficacy, and tolerance of berzosertib in oesophageal cancer (A1 cohort) with RT and advanced solid tumours (A2 cohort) with cisplatin and capecitabine. METHODS: Single-arm, open-label dose-escalation (Time-to-Event Continual Reassessment Method) trial with 16 patients in A1 and 18 in A2. A1 tested six dose levels of berzosertib with RT (35 Gy over 15 fractions in 3 weeks). RESULTS: No dose-limiting toxicities (DLTs) in A1. Eight grade 3 treatment-related AEs occurred in five patients, with rash being the most common. The highest dose (240 mg/m2) was determined as the recommended phase II dose (RP2D) for A1. Seven DLTs in two patients in A2. The RP2D of berzosertib was 140 mg/m2 once weekly. The most common grade ≥3 treatment-related AEs were neutropenia and thrombocytopenia. No treatment-related deaths were reported. CONCLUSIONS: Berzosertib combined with RT is feasible and well tolerated in oesophageal cancer patients at high palliative doses. Berzosertib with cisplatin and capecitabine was well tolerated in advanced cancer. Further investigation is warranted in a phase 2 setting. CLINICAL TRIALS IDENTIFIER: EU Clinical Trials Register (EudraCT) - 2015-003965-27 ClinicalTrials.gov - NCT03641547.

Polarization-sensitive tunable extraordinary terahertz transmission based on a hybrid metal-vanadium dioxide metasurface.

Thermally tunable extraordinary terahertz transmission in a hybrid metal-vanadium dioxide (VO2) metasurface is numerically demonstrated. The metasurface consists of a metal sheet perforated by square loops, while the loops are connected with strips of VO2. The frequency and amplitude of the transmission resonance are modulated by controlling the conductivity of VO2. For a y-polarized incident field, the resonance transmission peak redshifts from 0.88 to 0.81 THz upon insulator-to-metallic phase transition of VO2. For an x-polarized incident field, the transmission resonance at 0.81 THz is observed in the insulator phase. However, in the metallic phase of VO2, the electromagnetic field is effectively reflected in the 0.5-1.1 THz range with a transmission level lower than 0.14. The proposed metasurface can be utilized as a terahertz modulator, reconfigurable filter, or switch.

Hybrid plasmonic slot waveguide with a metallic grating for on-chip biosensing applications.

Designing reliable and compact integrated biosensors with high sensitivity is crucial for lab-on-a-chip applications. We present a bandpass optical filter, as a label-free biosensor, based on a hybrid slot waveguide on the silicon-on-insulator platform. The designed hybrid waveguide consists of a narrow silicon strip, a gap, and a metallic Bragg grating with a phase-shifted cavity. The hybrid waveguide is coupled to a conventional silicon strip waveguide with a taper. The effect of geometrical parameters on the performance of the filter is investigated by 3D finite-difference time-domain simulations. The proposed hybrid waveguide has potential for sensing applications since the optical field is pulled into the gap and outside of the silicon core, thus increasing the modal overlap with the sensing region. This biosensor offers a sensitivity of 270 nm/RIU, while it only occupies a compact footprint of 1.03µm×17.6µm.

C-type cytochrome-initiated reduction of bacterial lytic polysaccharide monooxygenases.

The release of glucose from lignocellulosic waste for subsequent fermentation into biofuels holds promise for securing humankind's future energy needs. The discovery of a set of copper-dependent enzymes known as lytic polysaccharide monooxygenases (LPMOs) has galvanised new research in this area. LPMOs act by oxidatively introducing chain breaks into cellulose and other polysaccharides, boosting the ability of cellulases to act on the substrate. Although several proteins have been implicated as electron sources in fungal LPMO biochemistry, no equivalent bacterial LPMO electron donors have been previously identified, although the proteins Cbp2D and E from Cellvibrio japonicus have been implicated as potential candidates. Here we analyse a small c-type cytochrome (CjX183) present in Cellvibrio japonicus Cbp2D, and show that it can initiate bacterial CuII/I LPMO reduction and also activate LPMO-catalyzed cellulose-degradation. In the absence of cellulose, CjX183-driven reduction of the LPMO results in less H2O2 production from O2, and correspondingly less oxidative damage to the enzyme than when ascorbate is used as the reducing agent. Significantly, using CjX183 as the activator maintained similar cellulase boosting levels relative to the use of an equivalent amount of ascorbate. Our results therefore add further evidence to the impact that the choice of electron source can have on LPMO action. Furthermore, the study of Cbp2D and other similar proteins may yet reveal new insight into the redox processes governing polysaccharide degradation in bacteria.

Management of bone metastasis and cancer treatment-induced bone loss during the COVID-19 pandemic: An international perspective and recommendations.

Optimum management of patients with cancer during the COVID-19 pandemic has proved extremely challenging. Patients, clinicians and hospital authorities have had to balance the risks to patients of attending hospital, many of whom are especially vulnerable, with the risks of delaying or modifying cancer treatment. Those whose care has been significantly impacted include patients suffering from the effects of cancer on bone, where delivering the usual standard of care for bone support has often not been possible and clinicians have been forced to seek alternative options for adequate management. At a virtual meeting of the Cancer and Bone Society in July 2020, an expert group shared experiences and solutions to this challenge, following which a questionnaire was sent internationally to the symposium's participants, to explore the issues faced and solutions offered. 70 respondents, from 9 countries (majority USA, 39%, followed by UK, 19%) included 50 clinicians, spread across a diverse range of specialties (but with a high proportion, 64%, of medical oncologists) and 20 who classified themselves as non-clinical (solely lab-based). Spread of clinician specialty across tumour types was breast (65%), prostate (27%), followed by renal, myeloma and melanoma. Analysis showed that management of metastatic bone disease in all solid tumour types and myeloma, adjuvant bisphosphonate breast cancer therapy and cancer treatment induced bone loss, was substantially impacted. Respondents reported delays to routine CT scans (58%), standard bone scans (48%) and MRI scans (46%), though emergency scans were less affected. Delays in palliative radiotherapy for bone pain were reported by 31% of respondents with treatments often involving only a single dose without fractionation. Delays to, or cancellation of, prophylactic surgery for bone pain were reported by 35% of respondents. Access to treatments with intravenous bisphosphonates and subcutaneous denosumab was a major problem, mitigated by provision of drug administration at home or in a local clinic, reduced frequency of administration or switching to oral bisphosphonates taken at home. The questionnaire also revealed damaging delays or complete stopping of both clinical and laboratory research. In addition to an analysis of the questionnaire, this paper presents a rationale and recommendations for adaptation of the normal guidelines for protection of bone health during the pandemic.

Subwavelength grating waveguide filter based on cladding modulation with a phase-change material grating.

Subwavelength engineering and utilizing phase-change materials with large contrast in their optical properties have become powerful design tools for integrated silicon photonics. Reversible phase-transition of phase-change materials such as Ge2Sb2Te5 (GST) provide a new degree of freedom and open up the possibility of adding new functionalities to the designed devices. We present an optical filter based on a silicon subwavelength grating (SWG) waveguide evanescently coupled to phase-change material loading segments arranged periodically around the SWG core. The effect of the GST loading segments' geometry and their distance from the SWG core on the filter's central wavelength and bandwidth are studied with three-dimensional finite-difference time-domain simulations. The employment of GST in the structure adds a switching functionality with an extinction ratio of 28.8 dB. We also examine the possibility of using the proposed structure as a reconfigurable filter by controlling the partial crystallization of the GST offering a blueshift of more than 4 nm.

Silicon nitride waveguide devices based on gradient-index lenses implemented by subwavelength silicon grating metamaterials.

The rapid development of photonic integrated circuits demands the design of efficient and compact waveguide devices such as waveguide tapers and crossings. Some components in the silicon nitride (SiN) waveguide platform are superior to their counterparts in the silicon waveguide platform. Designing a compact SiN waveguide taper and crossing is crucial to reduce the size of SiN photonic components. In this paper, we utilize the focusing property of the Luneburg lens to design an SiN taper connecting a 10-µm-wide waveguide to a 1-µm-wide waveguide. Three-dimensional full-wave simulations indicate that the designed 13-µm-long taper has an average transmission efficiency of 92% in the wavelength range of 1500-1600 nm. We also present an in-plane SiN waveguide crossing based on the imaging property of the square Maxwell's fisheye lens designed with quasi-conformal transformation optics. The designed waveguide crossing occupies a compact footprint of 5.65µm×5.65µm, while its average insertion loss is 0.46 dB in the bandwidth of 1500-1600 nm. To the best our knowledge, the designed SiN waveguide taper and crossing have the smallest footprints to date.

Engineering hemoglobin to enable homogenous PEGylation without modifying protein functionality.

In order to infuse hemoglobin into the vasculature as an oxygen therapeutic or blood substitute, it is necessary to increase the size of the molecule to enhance vascular retention. This aim can be achieved by PEGylation. However, using non-specific conjugation methods creates heterogenous mixtures and alters protein function. Site-specific PEGylation at the naturally reactive thiol on human hemoglobin (ßCys93) alters hemoglobin oxygen binding affinity and increases its autooxidation rate. In order to avoid this issue, new reactive thiol residues were therefore engineered at sites distant to the heme group and the α/ß dimer/dimer interface. The two mutants were ßCys93Ala/αAla19Cys and ßCys93Ala/ßAla13Cys. Gel electrophoresis, size exclusion chromatography and mass spectrometry revealed efficient PEGylation at both αAla19Cys and ßAla13Cys, with over 80% of the thiols PEGylated in the case of αAla19Cys. For both mutants there was no significant effect on the oxygen affinity or the cooperativity of oxygen binding. PEGylation at αAla19Cys had the additional benefit of decreasing the rates of autoxidation and heme release, properties that have been considered contributory factors to the adverse clinical side effects exhibited by previous hemoglobin based oxygen carriers. PEGylation at αAla19Cys may therefore be a useful component of future clinical products.

Polymer multimode waveguide bend based on a multilayered Eaton lens.

Reducing the bending radius of low-index-contrast waveguides is essential in reducing the size of the integrated optical components. A polymeric multimode waveguide bend is presented based on the Eaton lens. Ray-tracing calculations are utilized to truncate the Eaton lens in order to improve the performance of the bend. The truncation of the lens decreases the footprint of the bend as well. A designed waveguide bend with a radius of 18.4 µm is implemented by a concentric cylindrical multilayer structure. Average bend losses of 0.69 and 0.87 dB are achieved for the TM0 and TM1 modes, respectively, in the C-band of optical communication. The bend loss is lower than 1 dB in a bandwidth of 1520-1675 nm for both modes.

Multimode waveguide crossing based on a square Maxwell's fisheye lens.

Mode-division multiplexing (MDM) is an emerging large-capacity data communication technology utilizing orthogonal guiding modes as independent data streams. One of the challenges of multimode waveguide routing in MDM systems is decreasing the mode leakage of waveguide crossings. In this article, a square Maxwell's fish-eye lens as a waveguide crossing medium based on quasiconformal transformation optics is designed and implemented on a silicon-on-insulator platform. Two approaches were taken to realize the designed lens: graded photonic crystal and varying the thickness of the silicon slab waveguide. Three-dimensional numerical simulations show that the designed multimode waveguide crossing has an ultrawide bandwidth from 1260 to 1675 nm with a compact footprint of only 3.77×3.77 µm2. For the first three transverse electric modes (TE0, TE1, and TE2), the designed waveguide crossing exhibits an average insertion loss of 0.24, 0.55, and 0.45 dB; a crosstalk of less than -72, -61, and -27 dB; and a maximum return loss of 54, 53, and 30 dB, respectively. The designed waveguide crossing supports low-distortion pulse transmission with a high fidelity factor of 0.9857. Furthermore, the proposed method can be expanded to design waveguide crossings with an even higher number of supporting modes by increasing the size of the lens.

[The effects of corneal cross-linking on intraocular pressure measurement in keratoconus]. / Les effets du cross-linking cornéen sur la mesure de pression intra-oculaire dans le kératocône.

Cross-linking (CXL) is a technique whose design aims to achieve a specific goal: to harden the corneal tissue of eyes with a progressive form of keratoconus. Other indications are being investigated, such as treatment of infectious keratitis and prevention of corneal ectasia post corneal ablative refractive surgery. Hardening the cornea means changing its biomechanical properties. The existence of true corneal hardening after CXL would inevitably result in an increase in measured intraocular pressure (IOP). This would have a considerable impact in the screening and follow-up of glaucoma patients who have undergone cross-linking because of the central role of IOP measurement in glaucomatous pathology.

Comparison of the oxidative reactivity of recombinant fetal and adult human hemoglobin: implications for the design of hemoglobin-based oxygen carriers.

Hemoglobin (Hb)-based oxygen carriers (HBOCs) have been engineered to replace or augment the oxygen carrying capacity of erythrocytes. However, clinical results have generally been disappointing, in part due to the intrinsic oxidative toxicity of Hb. The most common HBOC starting material is adult human or bovine Hb. However, it has been suggested that fetal Hb may offer advantages due to decreased oxidative reactivity. Large-scale manufacturing of HBOC will likely and ultimately require recombinant sources of human proteins. We, therefore, directly compared the functional properties and oxidative reactivity of recombinant fetal (rHbF) and recombinant adult (rHbA) Hb. rHbA and rHbF produced similar yields of purified functional protein. No differences were seen in the two proteins in: autoxidation rate; the rate of hydrogen peroxide reaction; NO scavenging dioxygenase activity; and the NO producing nitrite reductase activity. The rHbF protein was: less damaged by low levels of hydrogen peroxide; less damaging when added to human umbilical vein endothelial cells (HUVEC) in the ferric form; and had a slower rate of intrinsic heme loss. The rHbA protein was: more readily reducible by plasma antioxidants such as ascorbate in both the reactive ferryl and ferric states; less readily damaged by lipid peroxides; and less damaging to phosphatidylcholine liposomes. In conclusion in terms of oxidative reactivity, there are advantages and disadvantages to the use of rHbA or rHbF as the basis for an effective HBOC.

Backbone resonance assignments of ferric human cytochrome c and the pro-apoptotic G41S mutant in the ferric and ferrous states.

Human cytochrome c is a multi-functional protein with key roles in both the mitochondrial electron transfer chain and in apoptosis. In the latter, a complex formed between the mitochondrial phospholipid cardiolipin and cytochrome c is crucial for instigating the release of pro-apoptotic factors, including cytochrome c, from the mitochondrion into the cytosol. The G41S mutant of human cytochrome c is the only known disease-related variant of cytochrome c and causes increased apoptotic activity in patients with autosomal dominant thrombocytopenia. NMR spectroscopy can be used to investigate the interaction of human cytochrome c with cardiolipin and the structural and dynamic factors, which may contribute to enhanced apoptotic activity for the G41S mutant. We present here essentially full backbone amide resonance assignments for ferric human cytochrome c (98 %) as well as assignments of both the ferric (92 %) and ferrous (95 %) forms of the G41S mutant. Backbone amide chemical shift differences between the wild type and G41S mutant in the ferric state reveals significant changes around the mutation site, with many other amides also affected. This suggests the possibility of increased dynamics and/or a change in the paramagnetic susceptibility tensor of the G41S mutant relative to the wild type protein.

The hydrogen-peroxide-induced radical behaviour in human cytochrome c-phospholipid complexes: implications for the enhanced pro-apoptotic activity of the G41S mutant.

We have investigated whether the pro-apoptotic properties of the G41S mutant of human cytochrome c can be explained by a higher than wild-type peroxidase activity triggered by phospholipid binding. A key complex in mitochondrial apoptosis involves cytochrome c and the phospholipid cardiolipin. In this complex cytochrome c has its native axial Met(80) ligand dissociated from the haem-iron, considerably augmenting the peroxidase capability of the haem group upon H2O2 binding. By EPR spectroscopy we reveal that the magnitude of changes in the paramagnetic haem states, as well as the yield of protein-bound free radical, is dependent on the phospholipid used and is considerably greater in the G41S mutant. A high-resolution X-ray crystal structure of human cytochrome c was determined and, in combination with the radical EPR signal analysis, two tyrosine residues, Tyr(46) and Tyr(48), have been rationalized to be putative radical sites. Subsequent single and double tyrosine-to-phenylalanine mutations revealed that the EPR signal of the radical, found to be similar in all variants, including G41S and wild-type, originates not from a single tyrosine residue, but is instead a superimposition of multiple EPR signals from different radical sites. We propose a mechanism of multiple radical formations in the cytochrome c-phospholipid complexes under H2O2 treatment, consistent with the stabilization of the radical in the G41S mutant, which elicits a greater peroxidase activity from cytochrome c and thus has implications in mitochondrial apoptosis.

[Evaluation of the care for diabetes patients by general practitioners in the province of Khourigba, Morocco]. / Evaluation de la prise en charge des diabétiques par le médecin généraliste dans la province de Khouribga (Maroc).

Diabetes is a disease of concern due to its increasing frequency and high cost of care. This cross-sectional study evaluated the types of care provided to diabetes patients in primary care for management of the condition. Between December 2010 and March 2011, 54 general practitioners (CPs) in health centres in Khouribga province were asked to complete a pretested questionnaire on their care of diabetes patients. For type 2 diabetes, 46% of the CPs would prescribe diet and lifestyle treatment alone. The practice setting influenced how treatment was managed for typel diabetes patients: 88.5% of rural doctors prescribed premixed insulin versus 58.3% of urban GPs (P = 0.02). Insulin analogues were prescribed by 20.8% of urban GPs as against 3.8% of rural GPs (P = 0.09). There are several shortcomings in the quality of care for diabetes patients. Training GPs could be a solution, especially with the lack of specialists in our country.

High incidence of hepatitis B infection after treatment for paediatric cancer at a teaching hospital in Baghdad.

This study estimated the incidence of viral hepatitis in children treated for cancer, to identify variables that could affect this incidence and to assess the role of hepatitis B virus (HBV) vaccination in preventing infection. Between September 2007 and June 2008, 256 children in the haemato-oncology unit at the Children's Welfare Teaching Hospital, Baghdad, were studied prospectively. Demographic and clinical data and vaccination history were recorded. Patients were tested for HBV at the time of diagnosis (all were negative) and after starting chemotherapy. On admission to the unit, 231 patients (90.2%) were revaccinated. At reassessment after treatment for cancer, HBV infection was found in 70 patients (27.3%). The variables that significantly increased the risk for HBV infection were a diagnosis of leukaemia and receiving more than 3 units of blood. A higher number of HBV vaccinations in hospital reduced the risk for HBV infection. The high rate of acquisition of HBV infection found in this study indicates the need for better screening of blood products and adherence to aseptic techniques in management of this group of patients.

The persisting burden of visceral leishmaniasis in Iraq: data of the National Surveillance System, 1990-2009.

Visceral leishmaniasis (VL) is an endemic parasitic disease transmitted by the bite of sand flies. To describe trends and demographics of reported VL cases, we reviewed surveillance data from 1990-2009. Reported VL incidence per 100 000 population was 2·6 in 2007, 3·1 in 2008, and 4·8 in 2009, mostly in children aged <5 years. The number of cases varied greatly in step with prevailing economic and security conditions, raising concerns about the completeness and quality of surveillance data. Nevertheless, we conclude that VL remains an important endemic disease in Iraq and that surveillance system is recovering the capacity to detect cases as the country experiences greater stability. We recommend conducting formal entomological investigations, and evaluating existing control measures.

An investigation into a cardiolipin acyl chain insertion site in cytochrome c.

Mitochondrial cytochrome c associates with the phosphoplipid cardiolipin (CL) through a combination of electrostatic and hydrophobic interactions. The latter occurs by insertion into cytochrome c of an acyl chain, resulting in the dissociation of the axial Met-80 heme-iron ligand. The resulting five coordinate cytochrome c/CL complex has peroxidatic properties leading to peroxidation of CL and dissociation of the complex. These events are considered to be pre-apoptotic and culminate with release of cytochrome c from the mitochondria into the cytoplasm. Two distinct surface regions on cytochrome c have been suggested to mediate CL acyl chain insertion and this study has probed one of these regions. We have constructed a series of alanine mutants aimed at disrupting a surface cleft formed between residues 67-71 and 82-85. The physicochemical properties, peroxidase activity, CL binding, and kinetics of carbon monoxide (CO) binding to the ferrous cytochrome c/CL complex have been assessed for the individual mutants. Our findings reveal that the majority of mutants are capable of binding CL in the same apparent stoichiometry as the wild-type protein, with the extent to which the Met-80 ligand is bound in the ferrous cytochrome c/CL complex being mutant specific at neutral pH. Mutation of the species conserved Arg-91 residue, that anchors the cleft, results in the greatest changes to physicochemical properties of the protein leading to a change in the CL binding ratio required to effect structural changes and to the ligand-exchange properties of the ferrous cytochrome c/CL complex.