Enzymatic activity of Lecithin:retinol acyltransferase: A thermostable and highly active enzyme with a likely mode of interfacial activation

Lecithin:retinol acyltransferase (LRAT) plays a major role in the vertebrate visual cycle. Indeed, it is responsible for the esterification of all-trans retinol into all-trans retinyl esters, which can then be stored in microsomes or further metabolized to produce the chromophore of rhodopsin. In the present study, a detailed characterization of the enzymatic properties of truncated LRAT (tLRAT) has been achieved using in vitro assay conditions. A much larger tLRAT activity has been obtained compared to previous reports and to an enzyme with a similar activity. In addition, tLRAT is able to hydrolyze phospholipids bearing different chain lengths with a preference for micellar aggregated substrates. It therefore presents an interfacial activation property, which is typical of classical phospholipases. Furthermore, given that stability is a very important quality of an enzyme, the influence of different parameters on the activity and stability of tLRAT has thus been studied in detail. For example, storage buffer has a strong effect on tLRAT activity and high enzyme stability has been observed at room temperature. The thermostability of tLRAT has also been investigated using circular dichroism and infrared spectroscopy. A decrease in the activity of tLRAT was observed beyond 70 °C, accompanied by a modification of its secondary structure, i.e. a decrease of its α-helical content and the appearance of unordered structures and aggregated β-sheets. Nevertheless, residual activity could still be observed after heating tLRAT up to 100 °C. The results of this study highly improved our understanding of this enzyme.     

Estimation of the HIV Basic Reproduction Number in Rural South West Uganda: 1991–2008

Background

The basic reproduction number, , is one of the many measures of the epidemic potential of an infection in a population. We estimate HIV over 18 years in a rural population in Uganda, examine method-specific differences in estimated , and estimate behavioural changes that would reduce below one.

Methods

Data on HIV natural history and infectiousness were collated from literature. Data on new sexual partner count were available from a rural clinical cohort in Uganda over 1991–2008. was estimated using six methods. Behavioural changes required to reduce below one were calculated.

Results

Reported number of new partners per year was 0 to 16 (women) and 0 to 80 (men). When proportionate sexual mixing was assumed, the different methods yielded comparable estimates. Assuming totally assortative mixing led to increased estimates in the high sexual activity class while all estimates in the low-activity class were below one. Using the “effective” partner change rate introduced by Anderson and colleagues resulted in estimates all above one except in the lowest sexual activity class. could be reduced below one if: (a) medium risk individuals reduce their partner acquisition rate by 70% and higher risk individuals reduce their partner acquisition rate by 93%, or (b) higher risk individuals reduce the partner acquisition rate by 95%.

Conclusions

The estimated depended strongly on the method used. Ignoring variation in sexual activity leads to an underestimation of . Relying on behaviour change alone to eradicate HIV may require unrealistically large reductions in risk behaviour, even though for a small proportion of the population. To control HIV, complementary prevention strategies such as male circumcision and HIV treatment services need rapid scale up.     

Streptococcus pneumoniae proteomics: determinants of pathogenesis and vaccine development

Streptococcus pneumoniae is a major pathogen that is responsible for a variety of invasive diseases. The bacteria gain entry initially by establishing a carriage state in the nasopharynx from where they migrate to other sites in the body. The worldwide distribution of the bacteria and the severity of the diseases have led to a significant level of interest in the development of vaccines against the bacteria. Current vaccines, based on the bacterial polysaccharide, have a number of limitations including poor immunogenicity and limited effectiveness against all pneumococcal serotypes. There are many challenges in developing vaccines that will be effective against the diverse range of isolates and serotypes for this highly variable bacterial pathogen. This review considers how proteomic technologies have extended our understanding of the pathogenic mechanisms of nasopharyngeal colonization and disease development as well as the critical areas in developing protein-based vaccines.     

Gene Expression Profiling and Secretome Analysis Differentiate Adult-Derived Human Liver Stem/Progenitor Cells and Human Hepatic Stellate Cells

Adult-derived human liver stem/progenitor cells (ADHLSC) are obtained after primary culture of the liver parenchymal fraction. The cells are of fibroblastic morphology and exhibit a hepato-mesenchymal phenotype. Hepatic stellate cells (HSC) derived from the liver non-parenchymal fraction, present a comparable morphology as ADHLSC. Because both ADHLSC and HSC are described as liver stem/progenitor cells, we strived to extensively compare both cell populations at different levels and to propose tools demonstrating their singularity.ADHLSC and HSC were isolated from the liver of four different donors, expanded in vitro and followed from passage 5 until passage 11. Cell characterization was performed using immunocytochemistry, western blotting, flow cytometry, and gene microarray analyses. The secretion profile of the cells was evaluated using Elisa and multiplex Luminex assays.Both cell types expressed α-smooth muscle actin, vimentin, fibronectin, CD73 and CD90 in accordance with their mesenchymal origin. Microarray analysis revealed significant differences in gene expression profiles. HSC present high expression levels of neuronal markers as well as cytokeratins. Such differences were confirmed using immunocytochemistry and western blotting assays. Furthermore, both cell types displayed distinct secretion profiles as ADHLSC highly secreted cytokines of therapeutic and immuno-modulatory importance, like HGF, interferon-γ and IL-10.Our study demonstrates that ADHLSC and HSC are distinct liver fibroblastic cell populations exhibiting significant different expression and secretion profiles.     

Examination into the gamma irradiation of activated sludge

This study has shown that the treatment of activated sludge by gamma irradiation resulted in a deterioration in the filterability, a decrease in the size of the floc particles and an increase in the organic matter present in the sludge supernatant. A significant difference was found between the results obtained for filamentous and non-filamentous sludges in relation to the amount of soluble polysaccharide produced.     

Does the dysregulation of matrix metalloproteinases contribute to recurrent implantation failure?

Introduction: The progress in in vitro fertilization (IVF) techniques for infertility management has led to the investigation of embryo implantation site proteins such as Matrix metalloproteinases (MMPs), which may have a key role in embryo-endometrium crosstalk and in the molecular mechanisms of the embryo implantation.

Areas covered: Numerous studies have generated much information concerning the relation between the different proteins at the site of implantation such as cytokines, growth factors, adhesion molecules and MMPs. However, the exact role of the MMPs in embryo implantation and the impact of their dysregulation in recurrent implantation failure have yet to be characterized.

Expert commentary: The proteomic investigation of the MMPs and their molecular pathways may enable scientists and clinicians to correct this dysregulation (via appropriate means of prevention and treatment), better manage embryo transfer during IVF cycles, and thus increase the ongoing pregnancy rate.     

Fate of heavy metals in vertical subsurface flow constructed wetlands treating secondary treated petroleum refinery wastewater in Kaduna,Nigeria

This study examined the performance of pilot-scale vertical subsurface flow constructed wetlands (VSF–CWs) planted with three indigenous plants, i.e. Typha latifolia, Cyperus alternifolius, and Cynodon dactylon, in removing heavy metals from secondary treated refinery wastewater under tropical conditions. The T. latifolia-planted VSF–CW had the best heavy metal removal performance, followed by the Cyperus alternifolius-planted VSF–CW and then the Cynodon dactylon-planted VSF–CW. The data indicated that Cu, Cr, Zn, Pb, Cd, and Fe were accumulated in the plants at all the three VSF–CWs. However, the accumulation of the heavy metals in the plants accounted for only a rather small fraction (0.09–16%) of the overall heavy metal removal by the wetlands. The plant roots accumulated the highest amount of heavy metals, followed by the leaves, and then the stem. Cr and Fe were mainly retained in the roots of T. latifolia, Cyperus alternifolius, and Cynodon dactylon (TF < 1), meaning that Cr and Fe were only partially transported to the leaves of these plants. This study showed that VSF–CWs planted with T. latifolia, Cyperus Alternifolius, and Cynodon dactylon can be used for the large-scale removal of heavy metals from secondary refinery wastewater.     

Le passage Cénomanien–Turonien dans le Nord-Ouest algérien (coupe de Douar Menkouchi,Ouarsenis) : biostratigraphie des radiolaires

The Ouarsenis Massif belongs to the Algerian Tell domain which is considered as the eastern part of the Maghrebian Tethys former margin. The Cenomanian-Turonian Douar Menkouchi section outcropping in the eastern side of the Ouarsenis massif is composed of marls and laminated limestone alternations, including massive limestone and a biosiliceous bed toward the upper part of the succession. It reveals the presence of well-preserved and diversified radiolarians. In this study, we have identified for the first time in the Algerian domain, age-diagnostic radiolarian assemblages characterizing the Cenomanian-Turonian transition (C/T). The organic-rich laminated beds (black shales) confined to Silvae Zone, Cenomanian in age and underlying a biosiliceous interval, have provided radiolarian assemblages dominated by Pseudodictyomitrae. The successions overlying the biosiliceous interval have provided diversified radiolarian assemblages including Hagiastridae (i,e. Crucella cachensis, Alievium cf. superbum) and abundant Dictymitrae taxa (i,e. Dictyomitra cf. napaensis and Dictyomitra undata) indicating early Turonian age. These marl-limestone alternations are assigned to the Alievium superbum Zone. Considering taphonomic and diagenetic implications on assemblages content, we conclude that organic-rich beds and biosiliceous interval outline the latest Cenomanian. The radiolarian assemblage composition exhibits similarities to microfauna recovered from Bonarelli Horizon in Central Italy. Morphological similarities are also deduced from assemblages containing Pseudodictyomitrae tiara morphotypes (synonym of P. nakasekoi) which resemble those recovered from ophiolitic intervals in Cyprus and Oman areas.