Structure of an As(III) S-Adenosylmethionine Methyltransferase: Insights into the Mechanism of Arsenic Biotransformation

Enzymatic methylation of arsenic is a detoxification process in microorganisms but in humans may activate the metalloid to more carcinogenic species. We describe the first structure of an As(III) S-adenosylmethionine methyltransferase by X-ray crystallography that reveals a novel As(III) binding domain. The structure of the methyltransferase from the thermophilic eukaryotic alga Cyanidioschyzon merolae reveals the relationship between the arsenic and S-adenosylmethionine binding sites to a final resolution of ～1.6 ?. As(III) binding causes little change in conformation, but binding of SAM reorients helix α4 and a loop (residues 49-80) toward the As(III) binding domain, positioning the methyl group for transfer to the metalloid. There is no evidence of a reductase domain. These results are consistent with previous suggestions that arsenic remains trivalent during the catalytic cycle. A homology model of human As(III) S-adenosylmethionine methyltransferase with the location of known polymorphisms was constructed. The structure provides insights into the mechanism of substrate binding and catalysis.     

Alanine scanning of all cysteines and construction of a functional cysteine-less Cdr1p, a multidrug ABC transporter of Candida albicans

Herein, we discuss the role of the native cysteines present in a major multidrug ABC transporter of Candida albicans, Cdr1p, and describe the construction of this transporter's functional cysteine-less (cysless) protein version for cross-linking studies. In the experiments in which all 23 cysteines were replaced individually, we observed that most of the cysteine replacements were tolerated by the protein, but the replacement of C1056, C1091, C1106, C1294 or C1336 resulted in an enhanced drug susceptibility together with an abrogated drug efflux. Notably, the ATPase activity was uncoupled, which largely remained unaffected in these variants. The substitution of the critical cysteines with serines restored the normal expression and functionality of Cdr1p because serine can effectively mimic the hydrogen bonding properties of cysteine. Finally, we constructed a functional cysless His-tagged Cdr1p in which all the cysteines of the native protein were replaced with alanines and the critical cysteines were replaced with serines. Notably, cysless GFP-tagged variant of Cdr1p was non-functional. The cysless His-tagged variant of Cdr1p is the first example of a cysless ABC transporter in yeast, and it will lead to a greater understanding of the architecture of this important protein and provide insight into the nature of drug binding and interdomain communication.     

Cyanide degradation by immobilized cells of Rhodococcus UKMP-5M

Anthropogenic sources contribute to the bulk presence of cyanide, which causes substantial health and environmental concerns. A petroleum-contaminated soil isolate, Rhodococcus UKMP-5M has been verified to efficiently degrade high concentration of cyanide in the form of KCN in our previous study. In order to enhance the cyanide-degrading ability of this bacterium, different encapsulation matrices were screened to immobilize cells of Rhodococcus UKMP-5M for degradation of cyanide. It was revealed that the biocatalyst activity and bead mechanical strength improved significantly when calcium alginate encapsulation technique was employed as compared to free cells. The results also indicated that the immobilized cell system could tolerate a higher level of KCN concentration and were able to support a higher biomass density. In addition, the embedded cells retained almost 96% of their initial cyanide removal efficiency during the first five batches and the entrapped cell system maintained 64% of its initial activity after eight successive batches. The encapsulated beads could be easily recovered from the production medium and reused for up to five batches without significant losses of cyanide-degrading ability, which proved to be advantageous from an economic point of view. From this study, it could be inferred that the novel Rhodococcus UKMP-5M strain demonstrated high cyanide-degrading ability and the optimized calcium alginate immobilization technique provided a promising alternative for practical application of large scale remediation of cyanide-bearing wastewaters.     

Salt tolerance of a cash crop halophyte Suaeda fruticosa: biochemical responses to salt and exogenous chemical treatments

Suaeda fruticosa Forssk is a leaf succulent obligate halophyte that produces numerous seeds under saline conditions. Seeds are a good source of high quality edible oil and leaves are capable of removing substantial amount of salt from the saline soil besides many other economic usages. Little is known about the biochemical basis of salt tolerance in this species. We studied some biochemical responses of S. fruticosa to different exogenous treatments under non-saline (0 mM), moderate (300 mM) or high (600 mM) NaCl levels. Eight-week-old seedlings were sprayed twice a week with distilled water, hydrogen peroxide (H₂O₂, 100 μM), glycine betaine (GB, 10 mM), or ascorbic acid (AsA, 20 mM) for 30 days. At moderate (300 mM) NaCl, leaf Na⁺, Ca²⁺ and osmolality increased, along with unchanged ROS and antioxidant enzyme activities, possibly causing a better plant growth. Plants grew slowly at 600 mM NaCl to avoid leaf Na⁺ buildup relative to those at 300 mM NaCl. Exogenous application of distilled water and H₂O₂ improved ROS scavenging mechanisms, although growth was unaffected. ASA and GB alleviated salt-induced growth inhibition at 600 mM NaCl through enhancing the antioxidant defense system and osmotic and ion homeostasis, respectively.     

Green composites from sustainable cellulose nanofibrils: A review

Green composites are materials having ecofriendly attributes that are technically and economically feasible while minimizing the generation of pollution. In this context it refers to the combination of fully degradable fibers mostly cellulosic materials and natural resins to develop green composite materials. In the past decade, overdependence on petroleum products (synthetic polymers, resins, etc.) has consistently increased and on account of this, the researchers are now focusing more on green materials specially cellulosics. Cellulosic fibers in micro and nano scale are attractive to replace man-made fibers as reinforcement to make environmentally friendly green products. In this study, we will discuss the processing, extraction, properties, chronological events and applications of cellulose and cellulosic-based nanocomposite materials. Cellulosic nanocomposites are currently considered one of the most promising areas of scientific and technological development in the field of plant products. The aim of this review is to demonstrate the current state of development in the field of cellulose nanofibril based green composites research and application through examples.     

Effect of culture media on expansion properties of human umbilical cord matrix-derived mesenchymal cells

Background aims. Mesenchymal stromal cells (MSC) have been isolated from a number of different tissues, including umbilical cord. Because of the lack of a uniform approach to human umbilical cord matrix-derived mesenchymal (hUCM) cell expansion, we attempted to identify the optimum conditions for the production of a high quantity of hUCM cells by comparing two media. Methods. We compared the ability of Dulbecco's Modified Eagle's Medium/F12 (DMEM/F12) and Alpha Minimum Essential Medium (α-MEM) with Glutamax (GL) (α-MEM/GL) to expand hUCM cells. For this purpose, hUCM cells were cultured in plates containing different culture media supplemented with 10% fetal bovine serum (FBS). Culture dishes were left undisturbed for 10-14 days to allow propagation of the newly formed hUCM cells. The expansion properties, CD marker expression, differentiation potential, population doubling time (PDT) and cell activity were compared between the two groups. Results. The hUCM cells harvested from each group were positive for MSC markers, including CD44, CD90 and CD105, while they were negative for the hematopoietic cell surface marker CD34. Differentiation into adipogenic and osteogenic lineages was confirmed for both treatments. Cell activity was higher in the α-MEM/GL group than the DMEM/F12 group. PDT was calculated to be 60 h for the DMEM/F12 group, while for the α-MEM/GL group it was 47 h. Conclusions. Our data reveal that α-MEM/GL with 10% FBS supports hUCM cell growth more strongly than DMEM/F12 with 10% FBS.     

The variation of tree beta diversity across a global network of forest plots

Aims With the aim of understanding why some of the world's forests exhibit higher tree beta diversity values than others, we asked: (1) what is the contribution of environmentally related variation versus pure spatial and local stochastic variation to tree beta diversity assessed at the forest plot scale; (2) at what resolution are these beta‐diversity components more apparent; and (3) what determines the variation in tree beta diversity observed across regions/continents? Location World‐wide. Methods We compiled an unprecedented data set of 10 large‐scale stem‐mapping forest plots differing in latitude, tree species richness and topographic variability. We assessed the tree beta diversity found within each forest plot separately. The non‐directional variation in tree species composition among cells of the plot was our measure of beta diversity. We compared the beta diversity of each plot with the value expected under a null model. We also apportioned the beta diversity into four components: pure topographic, spatially structured topographic, pure spatial and unexplained. We used linear mixed models to interpret the variation of beta diversity values across the plots. Results Total tree beta diversity within a forest plot decreased with increasing cell size, and increased with tree species richness and the amount of topographic variability of the plot. The topography‐related component of beta diversity was correlated with the amount of topographic variability but was unrelated to its species richness. The unexplained variation was correlated with the beta diversity expected under the null model and with species richness. Main conclusions Because different components of beta diversity have different determinants, comparisons of tree beta diversity across regions should quantify not only overall variation in species composition but also its components. Global‐scale patterns in tree beta diversity are largely coupled with changes in gamma richness due to the relationship between the latter and the variation generated by local stochastic assembly processes.     

Virulence profile of different phylogenetic groups of locally isolated community acquired uropathogenic E. coli from Faisalabad region of Pakistan

ABSTRACT: BACKGROUND: Uropathogenic E.coli (UPEC) are among major pathogens causing urinary tract infections. Virulence factors are mainly responsible for the severity of these emerging infections. This study was planned to investigate the distribution of virulence genes and cytotoxic effects of UPEC isolates with reference to phylogenetic groups (B2, B1, D and A) to understand the presence and impact of virulence factors in the severity of infection in Faisalabad region of Pakistan. METHODS: In this study phylogenetic analysis, virulence gene identification and cytotoxicity of 59 uropathogenic E.coli isolates obtained from non-hospitalized patients was studied. RESULTS: Among 59 isolates, phylogenetic group B2 (50%) was most dominant followed by groups A, B1 (19% each) and D (12 %). Isolates present in group D showed highest presence of virulence genes. The prevalence hlyA (37%) was highest followed by sfaDE (27%), papC (24%), cnf1 (20%), eaeA (19%) and afaBC3 (14%). Highly hemolytic and highly verotoxic isolates mainly belonged to group D and B2. We also found two isolates with simultaneous presence of three fimbrial adhesin genes present on pap, afa, and sfa operons. This has not been reported before and underlines the dynamic nature of these UPEC isolates. CONCLUSIONS: It was concluded that in local UPEC isolates from non-hospitalized patients, group B2 was more prevalent. However, group D isolates were most versatile as all were equipped with virulence genes and showed highest level of cytotoxicity.     

Selenium treatment alters phytochemical and biochemical activity of in vitro-grown tissues and organs of Allium sativum L.

Garlic, an important flavoring agent and a medicinally useful plant, can take up selenium from its immediate surrounding medium and incorporate it at high concentrations into amino acids and phytochemicals. Selenium, supplied as 0.5, 1.0, 2.0, and 4.0?mg?L^?1 Na₂SeO₃ increased the amino acid, protein, proline, and alliin content of in vitro-grown callus, embryo, plantlet, leaf, and root tissues of Allium sativum L. The enhancement was significant at 2 and 4?mg?L^?1. Superoxide dismutase, catalase, and glutathione reductase activities increased in all in vitro-grown tissues and organs with increasing selenium concentrations, but enzyme activity was highest with 4?mg?L^?1 selenium.