Role of the pleckstrin homology domain in intersectin-L Dbl homology domain activation of Cdc42 and signaling

Intersectin-long (ITSN-L) contains the invariant Dbl homology (DH) and pleckstrin homology (PH) domain structure characteristic of the majority of Dbl family proteins. This strict domain topography suggests that the PH domain serves an essential, conserved function in the regulation of the intrinsic guanine nucleotide exchange activity of the DH domain. We evaluated the role of the PH domain in regulating the DH domain function of ITSN-L. Surprisingly, we found that the PH domain was dispensable for guanine nucleotide exchange activity on Cdc42 in vitro, yet the PH domain enhanced the ability of the DH domain to activate Cdc42 signaling in vivo. PH domains can interact with phosphoinositide substrates and products of phosphatidylinositol 3-kinase (PI3K). However, PI3K activation did not modulate ITSN-L DH domain function in vivo.     

Solid-state 13C NMR spectroscopy studies of xylans in the cell wall of Palmaria palmata (L. Kuntze,Rhodophyta)

The chemical structure and interactions of the cell wall polysaccharides from the red edible seaweed Palmaria palmata were studied by liquid-like magic-angle-spinning (MAS) and cross-polarization MAS (CPMAS) solid-state 13C NMR spectroscopy. The liquid-like MAS and CPMAS 13C NMR spectra of the rehydrated algal powder revealed the presence of beta-(1-->4)/beta-(1-->3)-linked D-xylan with chemical shifts close to those observed in the solution 13C NMR spectrum of the polysaccharide. Observation of mix-linked xylan in the liquid-like MAS 13C NMR spectrum indicated that part of this cell wall polysaccharide is loosely held in the alga. The CPMAS NMR spectrum of the dry algal powder alcohol insoluble residue (AIR) showed broad peaks most of which corresponded to the mix-linked xylan. Hydration of AIR induced a marked increase in the signal resolution also in the CPMAS NMR spectra together with a shift of the C-3 and C-4 signals of the (1-->3)- and (1-->4)-linked xylose, respectively. Such modifications were present in the spectrum of hydrated (1-->3)-linked xylan from the green seaweed Caulerpa taxifolia and absent in that of (1-->4)-linked xylan from P. palmata. This result emphasizes the important role of (1-->3) linkages on the mix-linked xylan hydration-induced conformational rearrangement. The mix-linked xylan signals were observed in the CPMAS NMR spectrum of hydrated residues obtained after extensive extractions by NaOH or strong chaotropic solutions indicating strong hydrogen bonds or covalent linkages. T(1 rho) relaxations were measured close or above 10 ms for the mix-linked xylan in the dry and hydrated state in AIR and indicated that the overall xylan chains likely remain rigid. Rehydration of the mix-linked xylan lead to a decrease in the motion of protons bounded to the C-1 and C-4 carbons of the (1-->4)-linked xylose supporting the re-organization of the xylan chains under hydration involving junction-zones held by hydrogen bonds between adjacent (1-->4)-linked xylose blocks. The CPMAS NMR spectrum of both dry and rehydrated residues obtained after NaOH and HCl extractions demonstrated the presence of cellulose and (1-->4)-linked xylans. The structures of the different polysaccharides are discussed in relation to their interactions and putative functions on the cell wall mechanical properties in P. palmata.     

Evidence for glycosylphosphatidylinositol (GPI)-anchored eosinophil-derived neurotoxin (EDN) on human granulocytes

MIST (mast cell immunoreceptor signal transducer; also termed Clnk) is an adaptor protein structurally related to SLP-76-family hematopoietic cell-specific adaptor proteins. We demonstrate here that two major MIST-associated phosphoproteins expressed in mast cell lines are SLAP-130 and SKAP55, adaptors known to interact with the Src-homology (SH) 2 domain of Src-family protein tyrosine kinases (PTKs). MIST directly associated with SLAP-130 via its SH2 domain, and collaboration of SLAP-130 with SKAP55 was required for the recruitment of MIST to Lyn. Furthermore, MIST was preferentially recruited to Fyn rather than Lyn, which is regulated by higher affinity binding of SLAP-130 and SKAP55 with the Fyn-SH2 domain than the Lyn-SH2 domain. Our results suggest that the MIST–SLAP-130–SKAP55 adaptor complex functions downstream of high-affinity IgE receptor-associated Src-PTKs in mast cells.     

Phospholipid chlorohydrins cause ATP depletion and toxicity in human myeloid cells

Chlorohydrins of stearoyl-oleoyl phosphatidylcholine (SOPC), stearoyl-linoleoyl phosphatidylcholine, and stearoyl-arachidonyl phosphatidylcholine were incubated with cultured myeloid cells (HL60) for 24 h, and the cellular ATP level was measured using a bioluminescent assay. The chlorohydrins caused significant depletion of cellular ATP in the range 10–100 μM. The ATP depletion by the phospholipid chlorohydrins was slightly less than that of 4-hydroxy-2-nonenal, but greater than that of hexanal, trans-2-nonenal, and autoxidised palmitoyl-arachidonoyl phosphatidylcholine. SOPC chlorohydrin was also found to cause loss of viability in U937 cells, and thus phospholipid chlorohydrins could contribute to the formation of a necrotic core in advanced atherosclerotic lesions.     

Signal recognition particle (SRP)-mediated targeting and Sec-dependent translocation of an extracellular Escherichia coli protein

Hemoglobin protease (Hbp) is a hemoglobin-degrading protein that is secreted by a human pathogenic Escherichia coli strain via the autotransporter mechanism. Little is known about the earliest steps in autotransporter secretion, i.e. the targeting to and translocation across the inner membrane. Here, we present evidence that Hbp interacts with the signal recognition particle (SRP) and the Sec-translocon early during biogenesis. Furthermore, Hbp requires a functional SRP targeting pathway and Sec-translocon for optimal translocation across the inner membrane. SecB is not required for targeting of Hbp but can compensate to some extent for the lack of SRP. Hbp is synthesized with an unusually long signal peptide that is remarkably conserved among a subset of autotransporters. We propose that these autotransporters preferentially use the co-translational SRP/Sec route to avoid adverse effects of the exposure of their mature domains in the cytoplasm.     

RADACK, a stochastic simulation of hydroxyl radical attack to DNA

RADACK was conceived to simulate the radiation-induced attack to different DNA forms and complexes. It allows to separately calculate the probability of attack to each reactive atom of the sugar and of the base and takes into account the sequence-dependent structure of DNA as known from crystallographic or NMR studies or resulting from molecular modelling. The calculations are aimed to assess sequence-, structure- and ligand-dependent modulation of damages of sugar and bases, leading to single strand breaks (frank strand breaks, FSB) and alkali-labile base modifications (alkali-revealed breaks, ARB), respectively. The modelling procedure and the results of simulations for some representative structures (B, Z and quadruplex forms) are here described and discussed. The calculated relative probabilities of OH* radical attack to all reaction sites are compared to experimental FSB and ARB values. By a fitting procedure, the relative efficiencies of conversion of the C4' and C5'-centred radicals into FSB, epsilon (C4'): epsilon (C5'), and the relative efficiencies of base radicals- to- ARB conversion, epsilon(T) : epsilon(A) : epsilon(C) : epsilon(G), are then deduced for each DNA form. The ability of the model to account for the distribution of damages in DNA-ligand complexes is proven by its successful application to two DNA-protein systems : the lac repressor-lac operator complex and the nuclcosome core.     

Solution structure of a DNA duplex containing a formamide-adenine base pair

The N-(2-deoxy-beta3-D-erythro-pentofuranosyl) formamide residue results from a ring fragmentation product of thymine or cytosine. The presence of a formamide-adenine base pair in the sequence 5'd(AGGAACCACG).d(CGTGGFTCCT) has been studied by 1H and 31P nuclear magnetic resonance (NMR) and molecular dynamics. There are two possible isomers for the formamide side chain, either cis or trans. For each isomer, we observed an equilibrium in solution between two forms. First, a species where the formamide is intrahelical and paired with the facing adenine. For the cis isomer, the formamide is in a syn conformation and two hydrogen bonds with adenine are formed. The trans isomer is in an anti conformation and a single hydrogen bond is observed. In the second form, whatever the isomer, the formamide is rejected outside the helix, whereas the adenine remains inside.     

Integrin cytoplasmic domain-associated protein 1alpha (ICAP-1alpha ) interacts directly with the metastasis suppressor nm23-H2, and both proteins are targeted to newly formed cell adhesion sites upon integrin engagement

Cell adhesion-dependent signaling implicates cytoplasmic proteins interacting with the intracellular tails of integrins. Among those, the integrin cytoplasmic domain-associated protein 1alpha (ICAP-1alpha) has been shown to interact specifically with the beta(1) integrin cytoplasmic domain. Although it is likely that this protein plays an important role in controlling cell adhesion and migration, little is known about its actual function. To search for potential ICAP-1alpha-binding proteins, we used a yeast two-hybrid screen and identified the human metastatic suppressor protein nm23-H2 as a new partner of ICAP-1alpha. This direct interaction was confirmed in vitro, using purified recombinant ICAP-1alpha and nm23-H2, and by co-immunoprecipitation from CHO cell lysates over-expressing ICAP-1alpha. The physiological relevance of this interaction is provided by confocal fluorescence microscopy, which shows that ICAP-1alpha and nm23-H2 are co-localized in lamellipodia during the early stages of cell spreading. These adhesion sites are enriched in occupied beta(1) integrins and precede the formation of focal adhesions devoid of ICAP-1alpha and nm23-H2, indicating the dynamic segregation of components of matrix adhesions. This peripheral staining of ICAP-1alpha and nm23-H2 is only observed in cells spreading on fibronectin and collagen and is absent in cells spreading on poly-l-lysine, vitronectin, or laminin. This is consistent with the fact that targeting of both ICAP-1alpha and nm23-H2 to the cell periphery is dependent on beta(1) integrin engagement rather than being a consequence of cell adhesion. This finding represents the first evidence that the tumor suppressor nm23-H2 could act on beta(1) integrin-mediated cell adhesion by interacting with one of the integrin partners, ICAP-1alpha.     

Long-term protective and antigen-specific effect of heat-killed Mycobacterium vaccae in a murine model of allergic pulmonary inflammation

This report examines the effect of heat-killed Mycobacterium vaccae in a mouse model of allergic pulmonary inflammation. The s.c. administration of M. vaccae 3 wk before the immunization significantly reduced Ag-induced airway hyperreactivity and the increase in the numbers of eosinophils observed in the bronchoalveolar lavage fluid, blood, and bone marrow, even though no detectable changes in either cytokine (IL-4, IL-13, IL-5, and IFN-gamma) or total IgE levels were observed. Furthermore, transfer of splenocytes from OVA-immunized and M. vaccae-treated mice into recipient, OVA-immunized mice significantly reduced the allergen-induced eosinophilia by an IFN-gamma-independent mechanism, clearly indicating that the mechanism by which M. vaccae induces its inhibitory effect is not due to a redirection from a predominantly Th2 to a Th1-dominated immune response. The protective effect of M. vaccae on the allergen-induced eosinophilia lasted for at least 12 wk after its administration, and the treatment was also effective in presensitized mice. Moreover, the allergen specificity of the inhibitory effect could be demonstrated using a double-immunization protocol, where M. vaccae treatment before OVA immunization had no effect on the eosinophilic inflammation induced by later immunization and challenge with cockroach extract Ag. Taken together, these results clearly demonstrate that M. vaccae is effective in blocking allergic inflammation by a mechanism independent of IFN-gamma, induces long term and Ag-specific protection, and therefore has both prophylactic and therapeutic potential for the treatment of allergic diseases.     

Spontaneous lipid vesicle fusion with electropermeabilized cells

Fusion is obtained between electropermeabilized mammalian cells and intact large unilamellar lipid vesicles. This is monitored by a fluorescence assay. Prepulse contact is obtained by Ca2+ when negatively charged lipids are present in the liposomes. The mixing of the liposome content in the cell cytoplasm is observed under conditions preserving cell viability. Electric conditions are such that free liposomes are not affected by the external field. Therefore destabilization of only one of the two membranes of the partners is sufficient for fusion. The comparison between the efficiency of dye delivery for different liposome preparations (multilamellar vesicles, large unilamellar vesicles, small unilamellar vesicles) is indicative that more metastable liposomes are more fusable with electropulsated cells. This observation is discussed within the framework of the recent hypothesis that occurrence of a contact induced electrostatic destabilization of the plasma membrane is a key step in the exocytosis process.