The bacterial quorum-sensing signal molecule N-3-oxo-dodecanoyl-L-homoserine lactone reciprocally modulates pro- and anti-inflammatory cytokines in activated macrophages.

The bacterial molecule N-3-oxo-dodecanoyl-l-homoserine lactone (C12) has critical roles in both interbacterial communication and interkingdom signaling. The ability of C12 to downregulate production of the key proinflammatory cytokine TNF-α in stimulated macrophages was suggested to contribute to the establishment of chronic infections by opportunistic Gram-negative bacteria, such as Pseudomonas aeruginosa. We show that, in contrast to TNF-α suppression, C12 amplifies production of the major anti-inflammatory cytokine IL-10 in LPS-stimulated murine RAW264.

Phosphorylation of the integrase protein of coliphage HK022.

The integrase (Int) proteins of coliphages HK022 and lambda, are phosphorylated in one or more of their tyrosine residues. In Int of HK022 the phosphorylated residue(s) belong to its core-binding/catalytic domains. Wzc, a protein tyrosine kinase of Escherichia coli, is not required for Int phosphorylation in vivo, however, it can transphosphorylate the conserved Tyr(342) catalytic residue of Int in vitro.

Protein-protein interaction between monomers of coliphage HK022 excisionase.

Excisionase (Xis) is an accessory protein that is required for the site-specific excision reaction of the coliphages HK022 and lambda. Xis binds in a strong cooperative manner to two tandem binding sites (X1 and X2) located on the P arm of the attachment (att) sites on the phage genome. As a result of crosslinking experiments in vivo and in vitro of Xis-overexpressing cells, by gel filtration of purified Xis and by FRET analyses we show that Xis monomers of HK022 interact and form dimers that are not dependent on the single Cys residue of the protein and on the presence of DNA.

Activity of coliphage HK022 excisionase (Xis) in the absence of DNA binding.

A mutated excisionase (Xis) protein of coliphage HK022 whose single Cys residue was replaced by Ser does not bind to its two tandem binding sites (X1, X2) on the P arm of attR. Despite its DNA-binding inability the protein showed 30% excision activity of the wild type Xis both in vitro and in vivo. This partial activity is attributed to the interaction of Xis with integrase that is retained in the mutant protein.