Biotin-conjugated reagents as site-specific probes of membrane protein structure: application to the study of the human erythrocyte hexose transporter

A novel labeling procedure using biotin-conjugated protein-modifying reagents has been employed to study the structure and function of the human erythrocyte hexose transporter. The carbohydrate moiety of the isolated, reconstituted transporter was labeled by using galactose oxidase/biotin hydrazide. Cysteine residues, which are essential for transporter function, were tagged with a biotin-conjugated maleimide. Labeling with this reagent inhibited the binding of cytochalasin B to the transporter. Following sodium dodecyl sulfate-gel electrophoresis, labeling of the transporter and its proteolytic fragments was detected by Western blotting and probing with alkaline phosphatase-conjugated avidin. After tryptic cleavage of the transporter into two membrane domains, preparations reacted with galactose oxidase/biotin hydrazide were labeled on the 25-kDa glycosylated fragment, but not on the carbohydrate-free 19-kDa peptide. Biotin-maleimide-labeled cysteine residues on both peptides. Transporter polypeptide was fragmented more extensively using Staphylococcus aureus V8 protease. Limited digestion produced a broad band of 30-50 kDa and sharper bands of 23 and 21 kDa. More extensive digestion resulted in the disappearance of the 23-kDa peptide and the appearance of sharp bands of 20, 19, 17, 13, 11, 8, and 7 kDa. Biotin label introduced with galactose oxidase/biotin hydrazide was found on the broad 30-kDa band, confirming its identity as a glycopeptide. All of the peptides weighing more than 11 kDa contained cysteine residues labeled with biotin maleimide, while the 8- and 7-kDa peptides were unlabeled. These results demonstrate the potential usefulness of biotin-conjugated reagents as site-specific probes of membrane protein structure.     

Effects of habitat type change on taxonomic and functional composition of orchid bees (Apidae: Euglossini) in the Brazilian Amazon

Land use change impact species richness and functional diversity (FD). In the Brazilian Amazon, we examined the impacts of oil palm plantations on orchid bee (Apidae: Euglossini) species using abundance and FD. We collected male orchid bees in oil palm plantation (PALM), legal reserves (LR), and riparian corridors (APP), and then we used morphological and life-history traits to characterize each species. We evaluated differences in bee body size by comparing intertegular span values. We tested the influence of habitat on taxonomic and functional parameters of orchid bees by applying a partial redundancy analysis (pRDA). We contrasted FD by calculating species richness, functional richness, and functional dispersion. We sampled 1176 bees from 30 species in 18 sampling days across 2015 and 2016. Males from PALM were 13.6% bigger than those in LR areas, and bees from APP showed a similar pattern compared to LR and PALM. Less than 15% of the variation in species composition was related to the distance among sampling sites, and 8% was due to habitat structure. In our pRDA, the spatial difference explained 6% of the variation in orchid bee traits, but there were no effects of habitat parameters upon FD. FD was reduced with land use change caused by oil palm plantations. Our findings support the belief that many bees are impacted by cultivated lands. Nevertheless, the functional similarity between LRs and APPs reflects common structural elements between them, although we did not find significant relationship between functional composition and habitat structure that we evaluated.     

Isolation and partial characterization of components of Prunus avium L. styles,including an antigenic glycoprotein associated with a self-incompatibility genotype

Several components of buffer extracts of Prunus avium L. styles (cv. Lambert, S ₃ S ₄) have been isolated and partially characterized: the major component is a glycoprotein (molecular weight approx. 90,000; 95% protein, 5.4% carbohydrate). A sticky uronic-acid-containing component and an arabinogalactan are also present. Two minor components are an antigenic glycoprotein associated with the self-incompatibility genotype (Antigen S) and a component found in styles of all Prunus species (Antigen P). The isolated glycoproteins have a substantial carbohydrate content (Antigen P 17.2%; Antigen S 16.3%), and have apparent molecular weights of 32,000 (Antigen P) and 37,000–39,000 (Antigen S). They are antigenically quite distinct. Material corresponding to Antigen S is secreted into the medium of suspension-cultured callus cells raised from both leaf and stem of P. avium.Abbreviations DEAE diethylaminoethyl - SDS-PAGE sodium dodecylsulphate-polyacrylamide gel electrophoresis     

Nadph-initiated cytochrome P450-dependent free iron-independent microsomal lipid peroxidation: Specific prevention by ascorbic acid

In this paper we demonstrate that ascorbic acid specifically prevents NADPH-initiated cytochrome P450 (P450)-mediated microsomal lipid peroxidation in the absence of free iron. Lipid peroxidation has been evidenced by the formations of conjugated dienes, lipid hydroperoxide and malondialdehyde. Other scavengers of reactive oxygen species including superoxide dismutase, catalase, glutathione, -tocopherol, uric acid, thiourea, mannitol, histidine, -carotene and probucol are ineffective to prevent the NADPH-initiated P450-mediated free iron-independent microsomal lipid peroxidation. Using a reconstituted system comprised of purified NADPH-P450 reductase, P450 and isolated microsomal lipid or pure L--phosphatidylcholine diarachidoyl, a mechanism has been proposed for the iron-independent microsomal lipid peroxidation and its prevention by ascorbic acid. It is proposed that the perferryl moiety P450 Fe³⁺. O₂ initiates lipid peroxidation by abstracting methylene hydrogen from polyunsaturated lipid to form lipid radical, which then combines with oxygen to produce the chain propagating peroxyl radical for subsequent formation of lipid peroxides. Apparently, ascorbic acid prevents initiation of lipid peroxidation by interacting with P450 Fe³⁺. O₂. (Mol Cell Biochem 166: 35-44, 1997)     

Sterigmatocystin — incidence, fate and production byA versicolor in ras cheese

Sterigmatocystin (STG) is a toxic metabolite produced by severalAspergillus species. Because of its toxic and carcinogenic properties the occurrence of STG in food is considered to represent a potential hazard to man. The present study was designed to investigate following points:

Desulfotomaculum genus- and subgenus-specific 16S rRNA hybridization probes for environmental studies

Based on comparative analysis of 16S rRNA sequences and the recently established phylogeny of the genus Desulfotomaculum , a set of phylogenetically nested hybridization probes was developed and characterized. A genus-specific probe targets all known Desulfotomaculum species (with the exception of Desulfotomaculum acetoxidans ), and five specific probes target subclusters within the Desulfotomaculum genus. The dissociation temperature of each probe was determined experimentally. Probe specificities were verified through hybridizations with pure culture rRNA isolated from a wide variety of target and non-target organisms and through an evaluation of probe 'nesting' using samples obtained from four different environments. Fixation and hybridization conditions for fluorescence in situ hybridizations were also optimized. The probes were used in quantitative membrane hybridizations to determine the abundance of Desulfotomaculum species in thermophilic anaerobic digesters, in soil, in human faeces and in pig colon samples. Desulfotomaculum rRNA accounted for 0.3–2.1% of the total rRNA in the digesters, 2.6–6.6% in soil, 1.5–3.3% in human faeces and 2.5–6.2% in pig colon samples.     

Domain formation in models of the renal brush border membrane outer leaflet.

The plasma membrane outer leaflet plays a key role in determining the existence of rafts and detergent-resistant membrane domains. Monolayers with lipid composition mimicking that of the outer leaflet of renal brush border membranes (BBM) have been deposited on mica and studied by atomic force microscopy. Sphingomyelin (SM) and palmitoyloleoyl phosphatidylcholine (POPC) mixtures, at molar ratios varying from 2:1 to 4:1, were phase-separated into liquid condensed (LC) SM-enriched phase and liquid expanded (LE) POPC-enriched phase. The LC phase accounted for 33 and 58% of the monolayers surface for 2:1 and 4:1 mixtures, respectively. Addition of 20-50 mol % cholesterol (Chl) to the SM/POPC (3:1) mixtures induced marked changes in the topology of monolayers. Whereas Chl promoted the connection between SM domains at 20 mol %, increasing Chl concentration progressively reduced the size of domains and the height differences between the phases. Lateral heterogeneity was, however, still present at 33 mol % Chl. The results indicate that the lipid composition of the outer leaflet is most likely responsible for the BBM thermotropic transition properties. They also strongly suggest that the common maneuver that consists of depleting membrane cholesterol to suppress rafts does not abolish the lateral heterogeneity of BBM membranes.     

Activation of Protein Kinase C in Permeabilized Human Neuroblastoma SH-SY5Y Cells

The activation of protein kinase C was investigated in digitonin-permeabilized human neuroblastoma SH-SY5Y cells by measuring the phosphorylation of the specific protein kinase C substrate myelin basic protein4-14. The phosphorylation was inhibited by the protein kinase C inhibitory peptide PKC19-36 and was associated to a translocation of the enzyme to the membrane fractions of the SH-SY5Y cells. 1,2-Dioctanoyl-sn-glycerol had no effect on protein kinase C activity unless the calcium concentration was raised to concentrations found in stimulated cells (above 100 nM). Calcium in the absence of other activators did not stimulate protein kinase C. Phorbol 12-myristate 13-acetate was not dependent on calcium for the activation or the translocation of protein kinase C. The induced activation was sustained for 10 min, and thereafter only a small net phosphorylation of the substrate could be detected. Calcium or dioctanoylglycerol, when applied alone, only caused a minor translocation, whereas in combination a marked translocation was observed. Arachidonic acid (10 microM) enhanced protein kinase C activity in the presence of submaximal concentrations of calcium and dioctanoylglycerol. Quinacrine and p-bromophenacyl bromide did not inhibit calcium- and dioctanoylglycerol-induced protein kinase C activity at concentrations which are considered to be sufficient for phospholipase A2 inhibition.     

Gene conversion and natural selection in the evolution of X-linked color vision genes in higher primates

During higher primate evolution, gene conversion seems to have occurred often between the red and green photo-pigment genes, which are tandemly linked on the X chromosome. To understand this phenomenon better, intron 4 sequences of the red and green pigment genes of a male human (an Asian Indian), a male chimpanzee, and a male baboon were amplified by PCR and sequenced. The data show that the intron 4 sequences between the two genes have been strongly or completely homogenized in the three species studied. Apparently recent gene conversion events have occurred in introns 4 of the red and green pigment genes in humans and chimpanzees. Two or more conversion events may have occurred at different times in introns 4 of the two pigment genes in baboons. The divergence between the two genes is significantly lower in intron 4 than in exons 4 and 5 in each species, contrary to the usual situation that introns evolve faster than exons. It is most likely that strong natural selection for maintaining the distinct functions of exons 4 and 5 of the red and green pigment genes has acted against sequence homogenization of these exons.      

Liver Grafts for Transplantation from Donors with Diabetes: An Analysis of the Scientific Registry of Transplant Recipients Database

Patients with a history of diabetes mellitus (DM) have worse survival than those without DM after liver transplantation. However, the effect of liver grafts from DM donors on the post-transplantation survival of recipients is unclear. Using the Scientific Registry of Transplant Recipients database (2004–2008), 25,413 patients were assessed. Among them, 2,469 recipients received grafts from donors with DM. The demographics and outcome of patients were assessed. Patient survival was assessed using Kaplan–Meier methodology and Cox regression analyses. Recipients from DM donors experienced worse graft survival than recipients from non-DM donors (one-year survival: 81% versus 85%, and five-year survival: 67% versus 74%, P<0.001, respectively). Graft survival was significantly lower for recipients from DM donors with DM duration >5 years (P<0.001) compared with those with DM duration <5 years. Cox regression analyses showed that DM donors were independently associated with worse graft survival (hazard ratio, 1.11; 95% confidence interval, 1.02–1.19). The effect of DM donors was more pronounced on certain underlying liver diseases of recipients. Increases in the risk of graft loss were noted among recipients from DM donors with hepatitis-C virus (HCV) infection, whereas those without HCV experienced similar outcomes compared with recipients from non-DM donors. These data suggest that recipients from DM donors experience significantly worse patient survival after liver transplantation. However, in patients without HCV infection, using DM donors was not independently associated with worse post-transplantation graft survival. Matching these DM donors to recipients without HCV may be safe.