[show abstract][hide abstract] ABSTRACT: Staphylococcal gamma-hemolysins are bicomponent toxins forming a protein family with leucocidins and alpha-toxin. Two active toxins (AB and CB) can be formed combining one of the class-S components, HlgA or HlgC, with the class-F component HlgB. These two gamma-hemolysins form pores with marked similarities to alpha-toxin in terms of conductance, nonlinearity of the current-voltage curve, and channel stability in the open state. AB and CB pores, however, are cation-selective, whereas alpha-toxin is anion-selective. gamma-Hemolysins' pores are hetero-oligomers formed by three or four copies of each component (indicated as 3A3B and 3C3B or 4A4B and 4C4B). Point mutants located on a beta-strand of the class-S component that forms part of the protomer-protomer contact region can prevent oligomer assembly. Interestingly, these mutants inhibit growth of pores formed not only by their natural components but also by nonstandard components. This lead to the hypothesis that mixed ABC pores could also be formed. By studying the conductance of pores, assembled in the presence of all three components (in different ratios), it was observed that the magnitudes expected for mixed pores were, indeed, present. We conclude that the gamma-hemolysin/leucocidin bicomponent toxin family may form a larger than expected number of active toxins by cross-combining various S and F components.
Journal of Chemical Information and Modeling 10/2005; 45(6):1539-45. · 4.30 Impact Factor
[show abstract][hide abstract] ABSTRACT: Staphylococcus aureus γ-hemolysins (H1gA, H1gB and HlgC) and Panton-Valentine leucocidins (LukS-PV and LukF-PV) are bi-component toxins forming a protein family with some relationship to α-toxin. Active toxins are couples formed by taking one protein from each of the two subfamilies of the S-components (LukS-PV, H1gA and HlgC) and the F-components (LukF-PV and HlgB). We compared the mode of action of the six possible couples on leukocytes, red blood cells and model lipid membranes. All couples were leucotoxic on human monocytes, whereas only four couples (H1gA+H1gB, H1gC+H1gB, LukS-PV+H1gB and H1gA+LukF-PV) were hemolytic. Toxins H1gA+H1gB and H1gC+H1gB were also able to induce permeabilisation of model membranes by forming pores via oligomerisation. The presence of membrane-bound aggregates, the smallest and most abundant of which had molecular weight and properties similar to that formed by α-toxin, was detected by SDS-PAGE. By infrared spectroscopy in the attenuated total reflection configuration (FTIR-ATR), the secondary structure of both components and of the aggregate were determined to be predominantly β-sheet and turn with small variations among different toxins. Polarisation experiments indicated that the structure of the membrane complex was compatible with the formation of a β-barrel oriented perpendicularly to the plane of the membrane, similar to that of porins. The couple LukS-PV+LukF-PV was leucotoxic, but not hemolytic. When challenged against model membranes it was able to bind to the lipid vesicles and to form the aggregate with the β-barrel structure, but not to increase calcein permeability. Thus, the pore-forming effect correlated with the hemolytic, but not with the complete leucotoxic activity of these toxins, suggesting that other mechanisms, like the interaction with endogenous cell proteins, might also play a role in their pathogenic action.
Biochimica et Biophysica Acta (BBA) - Biomembranes. 01/1998;