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Biophysics of Proteins at Surfaces: Assembly, Activation, Signaling
Tuesday Speaker Abstracts
Surface Induced Oligomerisation--the Case of the Alpha-Toxin from S.aureus
Nadja Hellmann
, Markus Schwiering.
University of Mainz, Mainz, Germany.
Pore forming toxins can be found in many organisms from different taxa. Frequently the toxin is
a protein, which is secreted as a monomer, binds to the membrane and undergoes a
conformational towards a membrane-spanning pore. The alpha-toxin from S.aureus (Hla) is able
to lyse pure lipid membranes. We investigated the influence of the lipid membrane composition
on the oligomerisation level by employing fluorescence spectroscopy of pyren-labelled toxin,
SDS-gelelectrophoresis and fluorescence microscopy in order to find out whether the toxin has a
preference for regions with particular Lipid composition. Increasing concentration of cholesterol
and sphingomyelin (compared to phosphatidylcholine) facilitate oligomer formation and lysis in
phase separating lipid mixtures. On the first glance this seems to indicate, that a preference for
raft-structures exists.However, substitution of saturated SM by unsaturated SM (OSM=oleoyl
SM) showed that the fluid disordered phase in particular enhances oligomerisation [1]. Taken
together, these results indicate that this toxin tends to interact with or accumulate in the liquid
disordered phase rather than the liquid ordered phase. This is supported by fluorescence
microscopy. Simulations in comparison with experimental data indicate that oligomerisation
probability rather than monomer binding affinity is enhanced by presence of SM. Thus, in
contrast to some other pore forming toxins the preference for SM-containing lipid membranes
seems to be not a consequence of specific interaction of the lipid binding pocket of the toxin.
Possibly binding to SM keeps the toxin monomers in an orientation more suitable for
oligomerisation. This work was supported by the DFG (SFB 490). [1] Schwiering, M., A. Brack,
et al. (2013). "Lipid and phase specificity of alpha-toxin from S. aureus." Biochim Biophys Acta
1828(8): 1962-72.