SummarySubversion of host cell actin microfilaments is the hallmark of enterohaemorrhagic (EHEC) and enteropathogenic (EPEC) Escherichia coli infections. Both pathogens translocate the trans -membrane receptor protein -translocated intimin receptor (Tir), which links the extracellular bacterium to the cell cytoskeleton. While both converge on neural Wiskott-Aldrich syndrome protein (N-WASP), Tir-mediated actin accretion by EPEC and EHEC differ in that Tir EPEC requires both tyrosine phosphorylation and the host adaptor protein Nck, whereas Tir EHEC is not phosphorylated and utilizes an unidentified linker. Here we report the identification of Tir-cytoskeleton coupling protein (TccP), a novel EHEC effector that displays an Ncklike coupling activity following translocation into host cells. A tccP mutant did not affect Tir translocation and focusing but failed to recruit a a a a -actinin, Arp3, N-WASP and actin to the site of bacterial adhesion.When expressed in EPEC, bacterial-derived TccP restored actin polymerization activity following infection of an Nck-deficient cell line. TccP has a similar biological activity on infected human intestinal explants ex vivo . Purified TccP activates N-WASP stimulating, in the presence of Arp2/3, actin polymerization in vitro . These results show that EHEC translocates both its own receptor (Tir) and an Nck-like protein (TccP) to facilitate actin polymerization.

The dengue virus (DENV) NS3 protein is essential for viral polyprotein processing and RNA replication. It contains an N-terminal serine protease region (residues 1-168) joined to an RNA helicase (residues 180 -618) by an 11-amino acid linker (169 -179). The structure at 3.15 Å of the soluble NS3 protein from DENV4 covalently attached to 18 residues of the NS2B cofactor region (NS2B 18 NS3) revealed an elongated molecule with the protease domain abutting subdomains I and II of the helicase (Luo, D., Xu, T., Hunke, C., Grüber, G., Vasudevan, S. G., and Lescar, J. (2008) J. Virol. 82, 173-183). Unexpectedly, using similar crystal growth conditions, we observed an alternative conformation where the protease domain has rotated by ϳ161°with respect to the helicase domain. We report this new crystal structure bound to ADP-Mn 2؉ refined to a resolution of 2.2 Å . The biological significance for interdomain flexibility conferred by the linker region was probed by either inserting a Gly residue between Glu 173 and Pro 174 or replacing Pro 174 with a Gly residue. Both mutations resulted in significantly lower ATPase and helicase activities. We next increased flexibility in the linker by introducing a Pro 176 to Gly mutation in a DENV2 replicon system. A 70% reduction in luciferase reporter signal and a similar reduction in the level of viral RNA synthesis were observed. Our results indicate that the linker region has evolved to an optimum length to confer flexibility to the NS3 protein that is required both for polyprotein processing and RNA replication. Dengue virus (DENV)4 is an important vector-borne virus that causes a spectrum of illnesses in humans ranging from asymptomatic to severe disease, including dengue hemorrhagic fever and dengue shock syndrome. More than half of the ϳ70 members of the flavivirus genus that includes the four serotypes of DENV (DENV1-4), yellow fever virus, Japanese encephalitis virus, tick-borne encephalitis virus, and West Nile virus, are important human pathogens (1). The positive-sense flavivirus RNA genome of ϳ11 kb contains a single open reading frame that is translated into a polyprotein precursor, consisting of the structural proteins C, prM, and E and seven nonstructural proteins NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5. During viral replication, the polyprotein is cleaved by host proteases in the endoplasmic reticulum lumen and viral proteases at the cytoplasmic face (1). The NS3 protein (618 amino acids in DENV4) contains a serine-protease domain at its N terminus (whose activity requires the formation of a noncovalent complex with the central 40-residue hydrophilic segment of the membrane-bound NS2B protein cofactor) and an ATP-driven helicase and RNA triphosphatase at its C-terminal end. Atomic structures for the active NS3 protease domain (NS2B 47 NS3pro) (2-4), the ATPase/helicase domain (NS3hel) (5-9), and the full-length NS3 molecule fused to 18 residues of the NS2B cofactor (NS2B 18 NS3) (10) have been reported and reviewed (11). Together, these structures provide an explana...

Background: NS3-NS5 interaction is important for the dengue virus life cycle. Results: NS3 residue Asn-570 is essential for its interaction with NS5; mutation in an infectious cDNA abolished virus production and reduced positive-strand RNA synthesis. Conclusion: NS3-NS5 interaction may be required for coordinated positive-and negative-strand RNA synthesis. Significance: NS3-NS5 interaction may be a target for rational design of antiviral drugs.

Pileup of boron atoms near the maximum melt depth in bulk silicon and silicon-on-insulator (SOI) substrates upon laser annealing (LA) was studied. The results show that boron atoms accumulate near the maximum melt depth in shallow melting and increases with increasing laser pulses. The pileup is found to be related to the recrystallization behavior of the melted silicon during LA and occurs at a recrystallization transient, RT0, of about 10nm from the maximum melt depth in both SOI and bulk silicon substrates. An abrupt recrystallization process in preamorphized silicon, on the other hand, suppresses the formation of the boron pileup during LA.

Enterohemorrhagic Escherichia coli (EHEC) and enteropathogenic E. coli (EPEC) are diarrheagenic pathogens that colonize the gut through the formation of attaching and effacing lesions, which depend on the translocation of effector proteins via a locus of enterocyte effacement-encoded type III secretion system. Recently, two effector proteins, EspJ and TccP, which are encoded by adjacent genes on prophage CP-933U in EHEC O157:H7, have been identified. TccP consists of a unique N-terminus region and several proline-rich domains. In this project we determined the distribution of tccP in O157:H7, in non-O157 EHEC, and in typical and atypical EPEC isolates. All the EHEC O157:H7 strains tested were tccP ؉ . Unexpectedly, tccP was also found in non-O157 EHEC, and in typical and atypical EPEC isolates, particularly in strains belonging to serogroups O26 (EHEC), O119 (typical EPEC), and O55 (atypical EPEC). We recorded some variation in the length of tccP, which reflects diversity in the number of the proline-rich repeats. These results show the existence of a class of "attaching and effacing" pathogens which express a combination of EPEC and EHEC virulence determinants.