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The listeriolysin O (LLO) binding and pore formation at suboptimal pH and various cholesterol concentrations in vitro are investigated. The results show that LLO activity at physiological pH is important and that its action at sites far from the cell entry may have important physiological consequences for Listeria pathogenesis.

Model lipid membranes and their interaction with the pore-forming protein equinatoxin II (EqTxII) are discussed based on a calorimetric and spectroscopic study. Observations indicate that hydrophobic interactions are important in EqTxII-membrane association.

Differential scanning calorimetry, UV and CD spectroscopy and fluorescence emission spectroscopy was used to examine thermal denaturation of equinatoxin II (EqTxII), a globular protein, in glycine buffer solutions and triple distilled water. At temperatures lower than 60 degrees C, the protein exists in a native state with a low degree of ANS-binding, but undergoes a two-state conformational transition into an unfolded state at higher temperatures.

A study is conducted on pH-induced and thermally induced unfolding of ostreolysin by means of CD, UV absorption, and intrinsic typtophan fluorescence to characterize conformational transitions associated with its functional properties. Results indicate that the acid-induced molten globule-like state of ostreolysin is not relevant for lipid binding and pore formation.

The effect of sodium chloride (NaCl) on the thermodynamic and conformational properties of equinatoxin (EqTxII) at pH 3.0 is studied to investigate the oligomerization of its partially unfolded states. At pH 3.0 and high salt concentrations, the heat induced and partially unfolded state of EqTxII oligomerizes and forms non-native alpha-helical secondary structure.

The opportunistic pathogen Pseudomonas aeruginosa uses quorum-sensing systems to regulate collective behaviour in response to the environment, by linking the expression of particular genes to population density. The quorum-sensing transcription factors LasR and RhlR and their cognate N-acyl-homoserine lactone (HSL) signals N-3-oxo-dodecanoyl-L-HSL (3OC12-HSL) and N-butanoyl-L-HSL (C4-HSL) control the expression of several hundred genes, which include those involved in virulence and biofilm formation. Here, we have focused on regulation of the expression of the putative virulence factor gene, rahU. We show that the intact las-rhl box immediately upstream of the -35 promoter element is needed for rahU expression in P. aeruginosa. Using β-galactosidase assays and quantification of the mRNA levels for rahU, lasR and rhlR, we provide evidence that for rahU promoter activity, 3OC12-HSL-LasR is not sufficient, and instead C4-HSL-RhlR is the trigger. Furthermore, surface plasmon resonance analysis revealed that RahU binds the biosurfactant rhamnolipids. Thus, this is the first report of a bacterial molecule that interacts with RahU. [ABSTRACT FROM AUTHOR]

Disulfide pairings and active site residues are highly conserved in secretory phospholipases A(2) (PLA(2)s). However, secretory PLA(2)s of marine invertebrates display some distinctive structural features. In this study, we report the isolation and characterization of a PLA(2) from the northern Pacific sea anemone, Urticina crassicornis (UcPLA(2)), containing a C27N substitution and a truncated C-terminal sequence. This novel cnidarian PLA(2) shares about 60% identity and almost 70% homology with two putative PLA(2)s identified in the starlet sea anemone (Nematostella vectensis) genome project. UcPLA(2) lacks hemolytic and neurotoxic activities. A search of available sequences revealed that Asn27-'type' PLA(2)s are present in a few other marine animal species, including some vertebrates. The possibility that the C27N replacement represents a structural adaptation for PLA(2) digestion/activity in the marine environment was not supported by experiments testing the influence of ionic strength on UcPLA(2) enzymatic activity. Because of the highly divergent sequences among invertebrate group I PLA(2)s, it is currently not possible to identify orthologous relationships. As the Asn27-containing PLA(2)s are scattered among the other invertebrate group I PLA(2)s, they do not constitute a new, monophyletic PLA(2) clade.