P. aeruginosa SGNH Hydrolase-Like Proteins AlgJ and AlgX Have Similar Topology but Separate and Distinct Roles in Alginate Acetylation

The O-acetylation of polysaccharides is a common modification used by pathogenic organisms to protect against external forces. Pseudomonas aeruginosa secretes the anionic, O-acetylated exopolysaccharide alginate during chronic infection in the lungs of cystic fibrosis patients to form the major constituent of a protective biofilm matrix. Four proteins have been implicated in the O-acetylation of alginate, AlgIJF and AlgX. To probe the biological function of AlgJ, we determined its structure to 1.83 Å resolution. AlgJ is a SGNH hydrolase-like protein, which while structurally similar to the N-terminal domain of AlgX exhibits a distinctly different electrostatic surface potential. Consistent with other SGNH hydrolases, we identified a conserved catalytic triad composed of D190, H192 and S288 and demonstrated that AlgJ exhibits acetylesterase activity in vitro. Residues in the AlgJ signature motifs were found to form an extensive network of interactions that are critical for O-acetylation of alginate in vivo. Using two different electrospray ionization mass spectrometry (ESI-MS) assays we compared the abilities of AlgJ and AlgX to bind and acetylate alginate. Binding studies using defined length polymannuronic acid revealed that AlgJ exhibits either weak or no detectable polymer binding while AlgX binds polymannuronic acid specifically in a length-dependent manner. Additionally, AlgX was capable of utilizing the surrogate acetyl-donor 4-nitrophenyl acetate to catalyze the O-acetylation of polymannuronic acid. Our results, combined with previously published in vivo data, suggest that the annotated O-acetyltransferases AlgJ and AlgX have separate and distinct roles in O-acetylation. Our refined model for alginate acetylation places AlgX as the terminal acetlytransferase and provides a rationale for the variability in the number of proteins required for polysaccharide O-acetylation.     

Protein kinase C mediates human neutrophil cytotoxicity

Human neutrophils stimulated with phorbol myristate acetate were able to damage human erythroleukemic K562 cells, in the absence of specific antibody, as assessed by a two hour 51Cr release assay. Neutrophils treated with formyl-peptide fMet-Leu-Phe did not display tumoricidal response, but the addition of diacylglycerol kinase inhibitor R59022 together with formyl-peptide induced the cytotoxic capacity against tumor target cells. Phorbol ester is a potent activator of certain functions of neutrophils because of its ability to directly and irreversibly stimulate protein kinase C; formyl-peptide, on the contrary, activates protein kinase C by inducing a rapid and transient production of diacylglycerol, that is quickly metabolized. The addition of an inhibitor of diacylglycerol kinase, R59022, however potentiated the action of formyl-peptide. These results indicate that protein kinase C is involved in the tumoricidal activity of neutrophils against K562 cells, and that maximal activation of the enzyme is required to achieve the cytotoxic response.     

Heterogeneity of Proteinase Inhibitors in the Water-Soluble Organic Matrix from the Oyster Nacre

We extracted proteinase inhibitors from the nacre of the oyster Pinctada margaritifera with water. Mixing the nacre powder with water for 20 h led to a water-soluble fraction [0.24% (wt/wt) of nacre]. After dialysis of the water-soluble matrix through 6- to 8-kDa and 0.5-kDa membranes, the proteinase inhibitors were divided into low and high molecular weight fractions that contained inhibitors of papain, bovine cathepsin B, and human cathepsin L. We studied the heterogeneity of the inhibitors after separating the low molecular weight fraction according to charge and hydrophobicity. After multistep purification, mass spectrometry analysis revealed that a potent inhibitory fraction contained several molecules. This observation demonstrates the difficulties encountered in attempting to isolate individual metabolites from the complex mixture of molecules present in nacre matrix. Interestingly, the low molecular weight fraction contained specific inhibitors that could discern between cathepsin B and cathepsin L. The nacre organic inhibitors were active against several cysteine proteinases, yet they were more specific in relation to serine proteinases, because only proteinase K was inhibited. These results demonstrate, for the first time, the presence of active proteinase inhibitors in the mollusc shell, and it is possible that these inhibitors may play a role in either protection of proteins involved in shell formation or in defense against parasites, or both.     

Identification of CD8+ T cell epitopes within lytic antigens of human herpes virus 8

The human herpesvirus 8 (HHV-8) is a gamma herpesvirus with oncogenic potential which establishes a chronic infection that is normally controlled by the immune system of healthy individuals. In particular, CTL responses seem to play a key role in control of the infection. In this study, we characterized epitope-specific CTL responses in healthy HHV-8-seropositive individuals against four HHV-8 lytic Ags: open reading frames (ORF) 26, 70, K3, and K5. We found that the majority of subjects responded to at least one HHV-8 lytic Ag-derived epitope, and some of these epitopes represented dominant targets, suggesting that they could be relevant targets of CTL-mediated immunity in vivo, and may be involved in host control of HHV-8. Specifically, we identified three CTL epitopes from ORF 26, which are presented by HLA-A2, six CTL epitopes from ORF 70 presented by HLA-A2 (three epitopes), -A24 (two epitopes), and -B7 (one epitope), three CTL epitopes from ORF K3 presented by HLA-A2 (two epitopes) and -B7 (one epitope), and one HLA-A2 presented epitope derived from ORF K5. The identified epitopes may be regarded as useful tools for understanding the role of CTL responses to lytic Ags in individuals affected by HHV-8-associated disorders, and for the development of immunotherapies for the treatment/prevention of HHV-8-associated malignancies.     

Lymphocytes treated with natural alfa-interferon produce a chemotactic factor for human neutrophils

Lymphocytes stimulated with alfa-interferon released a chemotactic factor for neutrophils. The process was not inhibited by cycloheximide, whereas mepacrine completely inhibited release of the chemotactic activity. The chemotactic factor was resistant to storage, heat treatment and proteolysis. Recombinant alfa-interferon did not stimulate lymphocytes to release a neutrophil chemotactic factor.