Three-dimensional structure of the plant photosystem II reaction centre at 8 A resolution

Photosystem II is a multisubunit enzyme complex involved in plant photosynthesis. It uses solar energy to catalyse the breakdown of water to reducing equivalents and molecular oxygen. Native photosystem II comprises more than 25 different subunits, and has a relative molecular mass of more than 600K. Here we report the three-dimensional structure of a photosystem II subcomplex, containing the proteins D1, D2, CP47 and cytochrome b-559, determined by electron crystallography. This CP47 reaction centre, which has a relative molecular mass of 160K, can perform light-mediated energy and electron-transfer reactions but is unable to oxidize water. The complex contains 23 transmembrane alpha-helices, of which 16 have been assigned to the D1, D2 and CP47 proteins. The arrangement of these helices is remarkably similar to that of the helices in the reaction centres of purple bacteria and of plant photosystem I, indicating a common evolutionary origin for these assemblies. The map suggests that redox cofactors in the D1-D2 complex are located in positions analogous to those in the bacterial reaction centre, but the distance between the chlorophylls corresponding to the bacterial 'special pair' is significantly larger.     

Relation of stressors and depressive symptoms to clinical progression of viral illness

OBJECTIVE: The aim of this research was to determine whether and in whom stressors and depressive symptoms facilitate clinical recurrence of herpes simplex virus (HSV) and progression of HIV. METHOD: Meta-analytic techniques were used to review the relations of stressors and depressive symptoms to clinical recurrence of HSV in 16 published studies and to indicators of HIV progression in 19 published studies. The authors calculated average effect sizes, performed fixed effect and random effect inferential analyses, tested for heterogeneous findings, and identified potential moderating variables. RESULTS: Depressive symptoms were associated with a slightly increased risk of HSV recurrence and increased reports of HIV-related symptoms, whereas stressors were not. However, depressive symptoms were not associated with objective indicators of accelerated HIV progression. Stressor studies, especially those that ascertained population-specific life events, found numerical and functional decrements in circulating natural killer cell populations. The candidate moderators identified include, for HSV recurrence, age, sex, and medication status, and for HIV-related symptoms, age, race, disease stage, and co-infection with HSV. CONCLUSIONS: Depressive symptoms, but not stressors, increase the risk of HSV recurrence generally. Depressive symptoms do not appear to accelerate HIV progression ubiquitously, although they are associated with increased reporting of HIV-related symptoms. Future studies that ascertain population-specific stressors should determine whether reductions in cytotoxic lymphocytes influence HIV disease progression. Moreover, researcher should investigate the role of the identified moderators and recognize psychoimmune moderators in existing and novel study groups. These analyses could confirm that certain individuals are especially susceptible to the effects on disease progression of stressors, depressive symptoms, or both.     

Liver disease and compensatory growth: unexpected lessons from genetically altered mice

Over the last decade, several animal models have been established that permit exploration of liver biology and disease. Although these models have been developed using diverse strategies, including transgene targeting, homozygous gene disruption and administration of hepatotoxic chemicals, each approach creates an animal with hepatocyte damage, resulting in an hepatic microenvironment that supports proliferation of healthy hepatocytes. These models have been used to demonstrate: (1) the remarkable ability of adult hepatocytes to clonally proliferate in response to liver growth signals, (2) the effectiveness of transplanted donor hepatocytes in repopulating damaged liver parenchyma, and (3) the feasibility of reconstituting liver with xenogeneic hepatocytes. This paper reviews the development and use of these models, and outlines their potential future application to the study of hepatic stem cells, therapy of liver disease and hepatic toxicology.     

Detection of lead in environmental objects and biologic materials during monitoring]

The authors specified methods to detect lead in biologic materials. The quality control covered use of Russian and foreign standard samples, the results proved to agree. Lead was detected by AAS technique (direct and flow-type variants with preliminary concentration of lead) and ELRA method. The authors determined measurement limits sufficient for analysis of complex biologic materials. The measurement range for lead varied from 0.002 mg/kg (plants) to 3,000 mg/kg (soil); the range of serum lead levels was < 0.5-39 mg/dl.     

Hypermutability of mouse chromosome 2 during the development of x-ray-induced murine myeloid leukemia

In an effort to identify the precise role of a deletion at regions D-E of mouse chromosome 2 [del2(D-E)] during the development of radiation-induced myeloid leukemia, we conducted a serial sacrifice study in which metaphase chromosomes were examined by the G-banding technique. Such metaphase cells were collected from x-irradiated mice during the period of transformation of some of the normal hematopoietic cells to the fully developed leukemic phenotype. A group of 250 CBA/Ca male mice (10-12 weeks old) were exposed to a single dose of 2 Gy of 250-kilovolt-peak x-rays; 42 age-matched male mice served as controls. Groups of randomly selected mice were sacrificed at 20 hr, 1 week, and then at intervals of 3 months up to 24 months after x-irradiation. Slides for cytogenetic, hematological, and histological examination were prepared for each animal at each sacrifice time. An expansion of cells with lesions on one copy of chromosome 2 was evident in 20-25% of treated mice at each sacrifice time. The majority of such lesions were translocations at 2F or 2H, strongly suggesting hypermutability of these sites on mouse chromosome 2. No lesions were found in control mice. The finding leads to the possibility that genomic lesions close to 2D and 2E are aberrants associated with radiation leukemogenesis, whereas a single clone of cells with a del2(D-E) may lead directly to overt leukemia. The data also indicate that leukemic transformation arises from the cumulative effects of multiple genetic events on chromosome 2, reinforcing the thesis that multiple steps of mutation occur in the pathogenesis of cancer.     

Design and synthesis of a series of potent and orally bioavailable noncovalent thrombin inhibitors that utilize nonbasic groups in the P1 position

As part of an ongoing effort to prepare therapeutically useful orally active thrombin inhibitors, we have synthesized a series of compounds that utilize nonbasic groups in the P1 position. The work is based on our previously reported lead structure, compound 1, which was discovered via a resin-based approach to varying P1. By minimizing the size and lipophilicity of the P3 group and by incorporating hydrogen-bonding groups on the N-terminus or on the 2-position of the P1 aromatic ring, we have prepared a number of derivatives in this series that exhibit subnanomolar enzyme potency combined with good in vivo antithrombotic and bioavailability profiles. The oxyacetic amide compound 14b exhibited the best overall profile of in vitro and in vivo activity, and crystallographic studies indicate a unique mode of binding in the thrombin active site.     

Direction determination in the minus-end-directed kinesin motor ncd

Motor proteins of the kinesin superfamily transport intracellular cargo along microtubules. Although different kinesin proteins share 30-50% amino-acid identity in their motor catalytic cores, some move to the plus end of microtubules whereas others travel in the opposite direction. Crystal structures of the catalytic cores of conventional kinesin (a plus-end-directed motor involved in organelle transport) and ncd (a minus-end-directed motor involved in chromosome segregation) are nearly identical; therefore, the structural basis for their opposite directions of movement is unknown. Here we show that the ncd 'neck' made up of 13 class-specific residues next to the superfamily-conserved catalytic core, is essential for minus-end-directed motility, as mutagenesis of these neck residues reverses the direction of ncd motion. By solving the 2.5 A structure of a functional ncd dimer, we show that the ncd neck (a coiled-coil) differs from the corresponding region in the kinesin neck (an interrupted beta-strand), although both necks interact with similar elements in the catalytic cores. The distinct neck architectures also confer different symmetries to the ncd and kinesin dimers and position these motors with appropriate directional bias on the microtubule.     

5-HT1C receptor-mediated phosphoinositide hydrolysis in the rat choroid plexus after chronic treatment with clozapine

Chronic treatment with clozapine (14 days; 10 and 25 mg/kg/day) decreases 5-HT1C receptor density but not affinity in rat choroid plexus measured with [3H]mesulergine. We now report the effects of the same clozapine treatment regimens on the function of 5-HT1C receptors (measured by maximal stimulation of 5-HT1C receptor-mediated phosphoinositide hydrolysis) in relation to receptor changes in rat choroid plexus. Quantitative 5-HT1C receptor autoradiography indicated that chronic clozapine treatment decreased, in a dose-related manner, 5-HT1C receptor binding sites labeled by antagonist ([3H]mesulergine) and agonist ([125I](+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, [125I]DOI) radioligands. However, only the higher dose of clozapine decreased statistically significantly the maximal 5-HT1C receptor-mediated phosphoinositide hydrolysis response. Chronic administration of haloperidol (0.5 mg/kg/day) did not change any of the 5-HT1C receptor parameters. In conclusion, chronic clozapine treatment is able to modulate the function of 5-HT1C receptors. This further strengthens the possibility that 5-HT1C receptors may contribute to some of the atypical effects of clozapine.     

Molecular characterisation of a distinct South African cassava infecting geminivirus

African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV) are whitefly-transmitted geminiviruses (WTGs) which are widespread in cassava in Africa and cause serious yield losses. Recently, a new geminivirus affecting cassava in South Africa (SACMV) has been reported. In this work SACMV was found to have DNA-A and DNA-B components. Comparisons of amino acid sequences of the putative coat protein, and nucleotide sequences of the common region and a 687-bp DNA B fragment of SACMV with other WTGs, showed that SACMV clustered with the Old World subgroup of the Begomovirus genus of geminiviruses. Despite its bipartite nature, SACMV was most closely related to monopartite TYLCVs, but was sufficiently different to justify designating it as a distinct virus. In serological studies, SACMV grouped biologically with EACMV isolates.