Structure-function relations and application of the neisserial polysialyltransferase of serogroup B

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Efficient Shortest Paths in Scale-Free Networks with Underlying Hyperbolic Geometry

A common way to accelerate shortest path algorithms on graphs is the use of a bidirectional search, which simultaneously explores the graph from the start and the destination. It has been observed recently that this strategy performs particularly well on scale-free real-world networks. Such networks typically have a heterogeneous degree distribution (e.g., a power-law distribution) and high clustering (i.e., vertices with a common neighbor are likely to be connected themselves). These two properties can be obtained by assuming an underlying hyperbolic geometry. To explain the observed behavior of the bidirectional search, we analyze its running time on hyperbolic random graphs and prove that it is {O~}(n^{2 - 1/alpha} + n^{1/(2 alpha)} + delta_{max}) with high probability, where alpha in (0.5, 1) controls the power-law exponent of the degree distribution, and delta_{max} is the maximum degree. This bound is sublinear, improving the obvious worst-case linear bound. Although our analysis depends on the underlying geometry, the algorithm itself is oblivious to it

Efficient Shortest Paths in Scale-Free Networks with Underlying Hyperbolic Geometry

A common way to accelerate shortest path algorithms on graphs is the use of a bidirectional search, which simultaneously explores the graph from the start and the destination. It has been observed recently that this strategy performs particularly well on scale-free real-world networks. Such networks typically have a heterogeneous degree distribution (e.g., a power-law distribution) and high clustering (i.e., vertices with a common neighbor are likely to be connected themselves). These two properties can be obtained by assuming an underlying hyperbolic geometry. To explain the observed behavior of the bidirectional search, we analyze its running time on hyperbolic random graphs and prove that it is $\mathcal {\tilde O}(n^{2 - 1/\alpha} + n^{1/(2\alpha)} + \delta_{\max})$ with high probability, where $\alpha \in (0.5, 1)$ controls the power-law exponent of the degree distribution, and $\delta_{\max}$ is the maximum degree. This bound is sublinear, improving the obvious worst-case linear bound. Although our analysis depends on the underlying geometry, the algorithm itself is oblivious to it

Proteolytic Release of the Intramolecular Chaperone Domain Confers Processivity to Endosialidase F*S⃞

Endosialidases (endoNs), as identified so far, are tailspike proteins of bacteriophages that specifically bind and degrade the α2,8-linked polysialic acid (polySia) capsules of their hosts. The crystal structure solved for the catalytic domain of endoN from coliphage K1F (endoNF) revealed a functional trimer. Folding of the catalytic trimer is mediated by an intramolecular C-terminal chaperone domain. Release of the chaperone from the folded protein confers kinetic stability to endoNF. In mutant c(S), the replacement of serine 911 by alanine prevents proteolysis and generates an enzyme that varies in activity from wild type. Using soluble polySia as substrate a 3-times higher activity was detected while evaluation with immobilized polySia revealed a 190-fold reduced activity. Importantly, activity of c(S) did not differ from wild type with tetrameric sialic acid, the minimal endoNF substrate. Furthermore, we show that the presence of the chaperone domain in c(S) destabilizes binding to polySia in a similar way as did selective disruption of a polySia binding site in the stalk domain. The improved catalytic efficiency toward soluble polySia observed in these mutants can be explained by higher dissociation and association probabilities, whereas inversely, an impaired processivity was found. The fact that endoNF is a processive enzyme introduces a new molecular basis to explain capsule degradation by bacteriophages, which until now has been regarded as a result of cooperative interaction of tailspike proteins. Moreover, knowing that release of the chaperone domain confers kinetic stability and processivity, conservation of the proteolytic process can be explained by its importance in phage evolution

Dependence of GT3-FCHASE extension by purified B-PST on CMP-Neu5Ac concentration

<p><b>Copyright information:</b></p><p>Taken from "Biochemical characterization of a polysialyltransferase reveals novel functional motifs in bacterial sialyltransferases"</p><p></p><p>Molecular Microbiology 2007;65(5):1258-1275.</p><p>Published online Jan 2007</p><p>PMCID:PMC2169525.</p><p>© 2007 The Authors; Journal compilation © 2007 Blackwell Publishing Ltd</p> Purified B-polyST was incubated with GT3-FCHASE and CMP-Neu5Ac for 5 min as described in . The respective CMP-Neu5Ac concentrations are indicated. The reaction mixtures were then adjusted to 25% ethanol. The supernatants were applied to a DNA Pac PA-100 column and chromatographed with a gradient of NaNO according to and

Polysialylation controls dendritic cell trafficking by regulating chemokine recognition

The addition of polysialic acid to N- and/or O-linked glycans, referred to as polysialylation, is a rare posttranslational modification that is mainly known to control the developmental plasticity of the nervous system. Here we show that CCR7, the central chemokine receptor controlling immune cell trafficking to secondary lymphatic organs, carries polysialic acid. This modification is essential for the recognition of the CCR7 ligand CCL21. As a consequence, dendritic cell trafficking is abrogated in polysialyltransferase-deficient mice, manifesting as disturbed lymph node homeostasis and unresponsiveness to inflammatory stimuli. Structure-function analysis of chemokine-receptor interactions reveals that CCL21 adopts an autoinhibited conformation, which is released upon interaction with polysialic acid. Thus, we describe a glycosylation-mediated immune cell trafficking disorder and its mechanistic basis

Semi-quantitative PCR showing expression of polySTs and NCAM and Western blotting showing expression of polySia-NCAM in cell lines.

<p>A: C6-STX cells express ST8SiaII and NCAM, whereas C6-WT cells express NCAM only. B: SH-SY5Y and IMR-32 cells both express ST8SiaII and NCAM. Expression of ST8SiaIV was not detected in SH-SY5Y cells, and was barely detectable in IMR-32 cells. DLD-1 cells do not express NCAM or ST8SiaII. C: C6-STX, SH-SY5Y and IMR-32 cells all express polySia, whereas C6-WT and DLD-1 cells do not.</p

Effect of ST8SiaII inhibition on recovery of polySia expression following removal by endoN.

<p>C6-STX cells (left) and SH-SY5Y cells (right) immunolabelled with anti-polySia antibody (mAb 735) followed by incubation with TRITC-conjugated secondary antibody [PolySia orange; nuclei stained blue with DAPI]. (a) Negative control (absence of mAb 735); (b) Positive control (absence of endoN/CMP treatment) (c) Removal of polySia with EndoN (0.3 µg/mL); (d) PolySia recovery following 6 h incubation in absence of CMP; (e) PolySia recovery following 6 h incubation with CMP at 0.5 mM; (f) PolySia recovery following 6 h incubation with CMP at 5 mM. CMP clearly prevents the recovery of polySia on the cell surface following biological removal at 5 mM. Scale bar = 50 µm.</p

Effect of ST8SiaII inhibition on tumour cell migration.

<p>Effect of CMP treatment on the migration of C6-STX, C6-WT, SH-SY5Y, and DLD-1 cells as assessed by 2D migration assays. Confluent cell monolayers were incubated with fresh complete medium and re-population of scratched wounds after 24 h was assessed. Migration is expressed as a percentage of that observed with untreated cells for a given cell line (complete re-population). CMP treatment at all concentrations decreased the migration capacity of polySia-expressing SH-SY5Y and C6-STX cells in a concentration dependent manner. However, CMP treatment had no significant effect on the migration of C6-WT and DLD-1 cells even at high concentrations. C6-WT and DLD-1 cells do not express polySTs or polySia. Values shown are means ± S.D based on three independent experiments (* P < 0.01).</p