Characterization of Fibrinogen Binding by Glycoproteins Srr1 and Srr2 of Streptococcus agalactiae

The serine-rich repeat glycoproteins of Gram-positive bacteria comprise a large family of cell wall proteins. Streptococcus agalactiae (group B streptococcus, GBS) expresses either Srr1 or Srr2 on its surface, depending on the strain. Srr1 has recently been shown to bind fibrinogen, and this interaction contributes to the pathogenesis of GBS meningitis. Although strains expressing Srr2 appear to be hypervirulent, no ligand for this adhesin has been described. We now demonstrate that Srr2 also binds human fibrinogen and that this interaction promotes GBS attachment to endothelial cells. Recombinant Srr1 and Srr2 bound fibrinogen in vitro, with affinities of K_D = 2.1 × 10⁻⁵ and 3.7 × 10⁻⁶ m, respectively, as measured by surface plasmon resonance spectroscopy. The binding site for Srr1 and Srr2 was localized to tandem repeats 6–8 of the fibrinogen Aα chain. The structures of both the Srr1 and Srr2 binding regions were determined and, in combination with mutagenesis studies, suggest that both Srr1 and Srr2 interact with a segment of these repeats via a “dock, lock, and latch” mechanism. Moreover, properties of the latch region may account for the increased affinity between Srr2 and fibrinogen. Together, these studies identify how greater affinity of Srr2 for fibrinogen may contribute to the increased virulence associated with Srr2-expressing strains.     

NHERF2 Protein Mobility Rate Is Determined by a Unique C-terminal Domain That Is Also Necessary for Its Regulation of NHE3 Protein in OK Cells

Na⁺/H⁺ exchanger regulatory factor (NHERF) proteins are a family of PSD-95/Discs-large/ZO-1 (PDZ)-scaffolding proteins, three of which (NHERFs 1-3) are localized to the brush border in kidney and intestinal epithelial cells. All NHERF proteins are involved in anchoring membrane proteins that contain PDZ recognition motifs to form multiprotein signaling complexes. In contrast to their predicted immobility, NHERF1, NHERF2, and NHERF3 were all shown by fluorescence recovery after photobleaching/confocal microscopy to be surprisingly mobile in the microvilli of the renal proximal tubule OK cell line. Their diffusion coefficients, although different among the three, were all of the same magnitude as that of the transmembrane proteins, suggesting they are all anchored in the microvilli but to different extents. NHERF3 moves faster than NHERF1, and NHERF2 moves the slowest. Several chimeras and mutants of NHERF1 and NHERF2 were made to determine which part of NHERF2 confers the slower mobility rate. Surprisingly, the slower mobility rate of NHERF2 was determined by a unique C-terminal domain, which includes a nonconserved region along with the ezrin, radixin, moesin (ERM) binding domain. Also, this C-terminal domain of NHERF2 determined its greater detergent insolubility and was necessary for the formation of larger multiprotein NHERF2 complexes. In addition, this NHERF2 domain was functionally significant in NHE3 regulation, being necessary for stimulation by lysophosphatidic acid of activity and increased mobility of NHE3, as well as necessary for inhibition of NHE3 activity by calcium ionophore 4-Br-{"type":"entrez-nucleotide","attrs":{"text":"A23187","term_id":"833253","term_text":"A23187"}}A23187. Thus, multiple functions of NHERF2 require involvement of an additional domain in this protein.     

Characterization of the Yeast Actin Patch Protein App1p Phosphatidate Phosphatase

Yeast App1p is a phosphatidate phosphatase (PAP) that associates with endocytic proteins at cortical actin patches. App1p, which catalyzes the conversion of phosphatidate (PA) to diacylglycerol, is unique among Mg²⁺-dependent PAP enzymes in that its reaction is not involved with de novo lipid synthesis. Instead, App1p PAP is thought to play a role in endocytosis because its substrate and product facilitate membrane fission/fusion events and regulate enzymes that govern vesicular movement. App1p PAP was purified from yeast and characterized with respect to its enzymological, kinetic, and regulatory properties. Maximum PAP activity was dependent on Triton X-100 (20 mm), PA (2 mm), Mg²⁺ (0.5 mm), and 2-mercaptoethanol (10 mm) at pH 7.5 and 30 °C. Analysis of surface dilution kinetics with Triton X-100/PA-mixed micelles yielded constants for surface binding (K_s^A = 11 mm), interfacial PA binding (K_m^B = 4.2 mol %), and catalytic efficiency (V_max = 557 μmol/min/mg). The activation energy, turnover number, and equilibrium constant were 16.5 kcal/mol, 406 s⁻¹, and 16.2, respectively. PAP activity was stimulated by anionic lipids (cardiolipin, phosphatidylglycerol, phosphatidylserine, and CDP-diacylglycerol) and inhibited by zwitterionic (phosphatidylcholine and phosphatidylethanolamine) and cationic (sphinganine) lipids, nucleotides (ATP and CTP), N-ethylmaleimide, propranolol, phenylglyoxal, and divalent cations (Ca²⁺, Mn²⁺, and Zn²⁺). App1p also utilized diacylglycerol pyrophosphate and lyso-PA as substrates with specificity constants 4- and 7-fold lower, respectively, when compared with PA.     

Rapid Accumulation of Endogenous Tau Oligomers in a Rat Model of Traumatic Brain Injury: POSSIBLE LINK BETWEEN TRAUMATIC BRAIN INJURY AND SPORADIC TAUOPATHIES*

Traumatic brain injury (TBI) is a serious problem that affects millions of people in the United States alone. Multiple concussions or even a single moderate to severe TBI can also predispose individuals to develop a pathologically distinct form of tauopathy-related dementia at an early age. No effective treatments are currently available for TBI or TBI-related dementia; moreover, only recently has insight been gained regarding the mechanisms behind their connection. Here, we used antibodies to detect oligomeric and phosphorylated Tau proteins in a non-transgenic rodent model of parasagittal fluid percussion injury. Oligomeric and phosphorylated Tau proteins were detected 4 and 24 h and 2 weeks post-TBI in injured, but not sham control rats. These findings suggest that diagnostic tools and therapeutics that target only toxic forms of Tau may provide earlier detection and safe, more effective treatments for tauopathies associated with repetitive neurotrauma.     

Signal and preference divergence among populations of the non‐endemic basal Lake Malawi cichlid fish Astatotilapia calliptera (Perciformes: Cichlidae)

In Lake Malawi and Lake Victoria, cichlid fishes have diversified into hundreds of species, many reproductively isolated by mate choice. Territorial males tend to be more aggressive to similar‐coloured males, facilitating coexistence of divergent colour morphs or species. Behavioural mate choice and aggression biases of species and allopatric populations of specialized rocky shore cichlids are influenced by divergent signals such as male colour. Believed to be basal to the Lake Malawi haplochromine radiation, and inhabiting shallow weedy areas of the lake and neighbouring water bodies, Astatotilapia calliptera also shows allopatric variation in colour. Here, it is demonstrated that such signal divergence is associated with tendencies of females to mate with males of their own population and also for males to preferentially attack males of their own population, indicating that preference divergence related to signal divergence in allopatry may have operated throughout the adaptive radiation of the Malawian cichlids. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 180–188.     

Dysbiosis Signature of Fecal Microbiota in Colorectal Cancer Patients

The human gut microbiota is a complex system that is essential to the health of the host. Increasing evidence suggests that the gut microbiota may play an important role in the pathogenesis of colorectal cancer (CRC). In this study, we used pyrosequencing of the 16S rRNA gene V3 region to characterize the fecal microbiota of 19 patients with CRC and 20 healthy control subjects. The results revealed striking differences in fecal microbial population patterns between these two groups. Partial least-squares discriminant analysis showed that 17 phylotypes closely related to Bacteroides were enriched in the gut microbiota of CRC patients, whereas nine operational taxonomic units, represented by the butyrate-producing genera Faecalibacterium and Roseburia, were significantly less abundant. A positive correlation was observed between the abundance of Bacteroides species and CRC disease status (R?=?0.462, P?=?0.046?<?0.5). In addition, 16 genera were significantly more abundant in CRC samples than in controls, including potentially pathogenic Fusobacterium and Campylobacter species at genus level. The dysbiosis of fecal microbiota, characterized by the enrichment of potential pathogens and the decrease in butyrate-producing members, may therefore represent a specific microbial signature of CRC. A greater understanding of the dynamics of the fecal microbiota may assist in the development of novel fecal microbiome-related diagnostic tools for CRC.     

Two new species of the genus Rhynchitobius Sharp, 1889 (Coleoptera: Rhynchitidae) in Dominican amber

New species of rhynchitid weevils, Rhynchitobius tanyrhinus n. sp. and R. xuthocolus n. sp. (Coleoptera: Rhynchitidae) in the tribe Auletini are described from Dominican amber. The former species is characterized by a long rostrum, narrow pronotum and elytra, rugose elytral intervals and distinct elytral striae. The latter species has a short rostrum, wide antennal club, yellow legs, non-rugose elytral intervals and weak elytral striae. The present study describes the first representatives of the family Rhynchitidae from Dominican amber.     

The pEAQ vector series: the easy and quick way to produce recombinant proteins in plants

Promoter regions of six sugarcane Loading Stem Gene (ScLSG) alleles were analyzed using bioinformatic and transgenic approaches. Stable transgene expression analyses, on multiple independent lines per construct, revealed differences between ScLSG promoters in absolute levels and in tissue-selectivity of luciferase reporter activity. Four promoters drove peak expression in the sucrose-loading zone and maintained substantial expression throughout mature stems. One drove a pattern of gradual increase along the stem maturation profile. In general, stem: root expression ratio increased with plant age. The ScLSG5 promoter had the fewest light-enhanced and root-expression motifs in bioinformatic analysis, and drove the highest level and specificity of transgene expression in stems. This indicates the potential to further improve the stem specificity of ScLSG promoter sequences by eliminating enhancers of expression in other tissues. An intron in the 5′UTR was important for expression strength. The ScLSG promoters will be useful for research and biotechnology in sugarcane, where the tailored expression of transgenes in stems is important for enhanced accumulation of sugar or value-added products, and for development as a bioenergy feedstock.     

Importance of the methyl-citrate cycle on glycerol metabolism in the yeast Yarrowia lipolytica

A novel approach to trigger lipid accumulation and/or citrate production in vivo through the inactivation of the 2-methyl-citrate dehydratase in Yarrowia lipolytica was developed. In nitrogen-limited cultures with biodiesel-derived glycerol utilized as substrate, the Δphd1 mutant (JMY1203) produced 57.7 g/L of total citrate, 1.6-fold more than the wild-type strain, with a concomitant glycerol to citrate yield of 0.91 g/g. Storage lipid in cells increased at the early growth stages, suggesting that inactivation of the 2-methyl-citrate dehydratase would mimic nitrogen limitation. Thus, a trial of JMY1203 strain was performed with glycerol under nitrogen-excess conditions. Compared with the equivalent nitrogen-limited culture, significant quantities of lipid (up to ∼31% w/w in dry weight, 1.6-fold higher than the nitrogen-limited experiment) were produced. Also, non-negligible quantities of citric acid (up to ∼26 g/L, though 0.57-fold lower than the nitrogen-limited experiment) were produced, despite remarkable nitrogen presence into the medium, indicating the construction of phenotype that constitutively accumulated lipid and secreted citrate in Y. lipolytica during growth on waste glycerol utilized as substrate.