Supramolecular structures of thylakoid membrane protein complexes:supercomplex organization under different environmental conditions

In this dissertation electron microscopy has been used as a main technique for structural characterization of the photosynthetic protein complexes isolated from different organisms. The photosynthetic processes are conducted by membrane-embedded protein complexes in the thylakoid membrane, known as photosystem I and II (PSI and PSII). The structural organization and architecture of the photosystems varies depending on species and the photic environment. In the first study, knock-out mutants of the moss Physcomitrella patens reveal the role of subunit Lhcb9 in regulation of the antenna size under low light conditions. Similarly, in a following study of the isolated supercomplexes from Norway spruce we show the presence of large PSII supercomplexes and PSII megacomplexes, while PSI binds multiple LHCII trimers under varying light adaptation conditions. Another study represents the organization and size of light-harvesting antenna of PSI from the colonial green alga Botryococcus braunii. Based on electron microscopy analysis, we concluded that the larger light-harvesting antenna in Botryococcus braunii is important for the cells in the interior of a colony. Our study on the diatom Thalassiosira pseudonana revealed the presence of a larger PSI and a unique PSII structure which might be necessary for capturing and regulation of the excitation energy. The structural characterization of Chlorella ohadii PSI shows an additional core subunit PsaM and also pigments bound to the antenna proteins which enable a high photosynthetic performance under extreme light intensities in the desert

Revealing the architecture of the photosynthetic apparatus in the diatom Thalassiosira pseudonana

Diatoms are a large group of marine algae that are responsible for about one-quarter of global carbon fixation. Light-harvesting complexes of diatoms are formed by the fucoxanthin chlorophyll a/c proteins and their overall organization around core complexes of photosystems (PSs) I and II is unique in the plant kingdom. Using cryo-electron tomography, we have elucidated the structural organization of PSII and PSI supercomplexes and their spatial segregation in the thylakoid membrane of the model diatom species Thalassiosira pseudonana. 3D sub-volume averaging revealed that the PSII supercomplex of T. pseudonana incorporates a trimeric form of light-harvesting antenna, which differs from the tetrameric antenna observed previously in another diatom, Chaetoceros gracilis. Surprisingly, the organization of the PSI supercomplex is conserved in both diatom species. These results strongly suggest that different diatom classes have various architectures of PSII as an adaptation strategy, whilst a convergent evolution occurred concerning PSI and the overall plastid structure

Pathophysiology and management of spontaneous intracranial hypotension--a review

Spontaneous Intracranial Hypotension is a syndrome involving reduced intracranial pressure secondary to a dural tear which occurs mostly due to connective tissue disorders such as Marfans Syndrome, and Ehler Danlos Syndrome. Patients with dural ectasias leading to CSF leakage into the subdural or epidural space classically present with orthostatic headaches and cranial nerve deficits mostly seen in cranial nerves V-VIII. Diagnosis of SIH is confirmed with the aid of neuroimaging modalities of which Cranial MR imaging is most widely used. SIH can be treated conservatively or with epidural blood patches which are now widely being used to repair dural tears, and their effectiveness is being recognized. Recently epidural injection of fibrin glue has also been used which has been found to be effective in certain patients

Unique organization of photosystem II supercomplexes and megacomplexes in Norway spruce

Photosystem II (PSII) complexes are organized into large supercomplexes with variable amounts of light-harvesting proteins (Lhcb). A typical PSII supercomplex in plants is formed by four trimers of Lhcb proteins (LHCII trimers), which are bound to the PSII core dimer via monomeric antenna proteins. However, the architecture of PSII supercomplexes in Norway spruce[Picea abies (L.) Karst.] is different, most likely due to a lack of two Lhcb proteins, Lhcb6 and Lhcb3. Interestingly, the spruce PSII supercomplex shares similar structural features with its counterpart in the green alga Chlamydomonas reinhardtii [Kouřil et al. (2016) New Phytol. 210, 808–814]. Here we present a single-particle electron microscopy study of isolated PSII supercomplexes from Norway spruce that revealed binding of a variable amount of LHCII trimers to the PSII core dimer at positions that have never been observed in any other plant species so far. The largest spruce PSII supercomplex, which was found to bind eight LHCII trimers, is even larger than the current largest known PSII supercomplex from C. reinhardtii. We have also shown that the spruce PSII supercomplexes can form various types of PSII megacomplexes, which were also identified in intact grana membranes. Some of these large PSII supercomplexes and megacomplexes were identified also in Pinus sylvestris, another representative of the Pinaceae family. The structural variability and complexity of LHCII organization in Pinaceae seems to be related to the absence of Lhcb6 and Lhcb3 in this family, and may be beneficial for the optimization of light-harvesting under varying environmental conditions

Lipid polymorphism of the subchloroplast—granum and stroma thylakoid membrane–particles. II. structure and functions

In Part I, by using (31)P-NMR spectroscopy, we have shown that isolated granum and stroma thylakoid membranes (TMs), in addition to the bilayer, display two isotropic phases and an inverted hexagonal (H(II)) phase; saturation transfer experiments and selective effects of lipase and thermal treatments have shown that these phases arise from distinct, yet interconnectable structural entities. To obtain information on the functional roles and origin of the different lipid phases, here we performed spectroscopic measurements and inspected the ultrastructure of these TM fragments. Circular dichroism, 77 K fluorescence emission spectroscopy, and variable chlorophyll-a fluorescence measurements revealed only minor lipase- or thermally induced changes in the photosynthetic machinery. Electrochromic absorbance transients showed that the TM fragments were re-sealed, and the vesicles largely retained their impermeabilities after lipase treatments—in line with the low susceptibility of the bilayer against the same treatment, as reflected by our (31)P-NMR spectroscopy. Signatures of H(II)-phase could not be discerned with small-angle X-ray scattering—but traces of H(II) structures, without long-range order, were found by freeze-fracture electron microscopy (FF-EM) and cryo-electron tomography (CET). EM and CET images also revealed the presence of small vesicles and fusion of membrane particles, which might account for one of the isotropic phases. Interaction of VDE (violaxanthin de-epoxidase, detected by Western blot technique in both membrane fragments) with TM lipids might account for the other isotropic phase. In general, non-bilayer lipids are proposed to play role in the self-assembly of the highly organized yet dynamic TM network in chloroplasts

Design and evaluation of power budget for a bidirectional CWDM-Passive Optical Network

Various PON technologies have been deployed recently but still they do not meet the high bandwidth demand at the access side. A bidirectional CWDM-PON system has been designed in this research paper. The bandwidth handling capability of the system is evaluated for a distance of 20km. Power budget is also investigated by calculating the overall power loss budget. The results show that the designed setup has the capability to withstand 64 ONUs for the uplink and 64 for the downlink with an acceptable value of BER

Scalable nonlinear equalization in high-bit-rate optical transmission systems

In this paper, we report on the performance comparison of all-optical signal processing methodologies to compensate fiber transmission impairments, namely chromatic dispersion and nonlinear distortion caused by the Kerr effect, in a coherent 112 Gbit/s dual-polarization 64 bit quadrature amplitude modulation system over 800 km standard single-mode fiber. We numerically compare optical backward propagation (OBP) with optical phase conjugation (OPC) techniques, namely. mid-link spectral inversion, predispersed spectral inversion, and OPC with nonlinearity module. We also evaluate a self-phase-modulation-based optical limiter with an appropriate prechirping to compensate for the intensity fluctuations as a hybrid approach with OBP. The results depict improvement in system performance by a factor of ∼4 dB of signal input power by all-optical signal processing methods, which is comparative with ideal digital backward propagation where the high complexity is the intrinsic impediment in the real-time implementation of the technique with coherent receivers

A curious case of primary gastric mucosal melanoma

Malignant melanoma is a neoplasm of melanin-producing cells predominantly of cutaneous origin, which uncommonly develops within gut mucosa. We present the case of a 58-year-old woman with complaints of abdominal pain, loss of appetite and weight. Esophagogastroduodenoscopy revealed a gastric mass and systemic imaging demonstrated widespread nodal and bilateral adrenal gland involvement. Histopathology of the gastric mass confirmed primary malignant mucosal melanoma of the stomach. The patient received three cycles of Nivolumab but did not respond, and thus, was then offered best supportive care. Although infrequent, mucosal melanoma can arise from the gastrointestinal tract, and in contrast to the cutaneous form, advanced disease usually has a dismal prognosis and responds poorly to immune checkpoint inhibitors. Primary gastric melanoma is an aggressive disease that is diagnosed by exclusion after the differential diagnosis of metastasis from a cutaneous or unknown primary site has been conducted. If available, patients with treatment-naïve mucosal melanoma should be considered for enrollment in clinical trials

Disseminated candidiasis: A rare presentation of acute leukemia

Disseminated fungal disease most commonly found in patients with hematologic malignancies or immunecompromised state, is rarely seen. Though the reported prevalence ranges from 20% to 40%, most fungal microabscesses occur in leukemic patients and are caused by candida albicans; others include cryptococcosis, mucormycosis and histoplasmosis. Hepatosplenic candidiasis also known as chronic disseminated candidiasis has been described in patients with acute leukemia following recovering from neutropenia, pathogenesis of which is not understood, thought to be due to exacerbated inflammatory reaction resulting in an immune reconstitution inflammatory syndrome. The purpose of presenting this case is to describe variable presentation of disseminated candidiasis which can be presenting feature of acute leukemia even without neutropenia and atypical radiological pattern in hepatosplenic candidiasis

PSI of the colonial alga Botryococcus braunii has an unusually large antenna size

PSI is an essential component of the photosynthetic apparatus of oxygenic photosynthesis. While most of its subunits are conserved, recent data have shown that the arrangement of the light-harvesting complexes I (LHCIs) differs substantially in different organisms. Here we studied the PSI-LHCI supercomplex of Botryococccus braunii, a colonial green alga with potential for lipid and sugar production, using functional analysis and single-particle electron microscopy of the isolated PSI-LHCI supercomplexes complemented by time-resolved fluorescence spectroscopy in vivo. We established that the largest purified PSI-LHCI supercomplex contains 10 LHCIs (;240 chlorophylls). However, electron microscopy showed heterogeneity in the particles and a total of 13 unique binding sites for the LHCIs around the PSI core. Time-resolved fluorescence spectroscopy indicated that the PSI antenna size in vivo is even larger than that of the purified complex. Based on the comparison of the known PSI structures, we propose that PSI in B. braunii can bind LHCIs at all known positions surrounding the core. This organization maximizes the antenna size while maintaining fast excitation energy transfer, and thus high trapping efficiency, within the complex