title: Tertiary structural changes of the alpha-hemolysin from Staphylococcus aureus on association with liposome membranes.
abstract: The interaction of alpha-hemolysin (also called alpha-toxin) from Staphylococcus aureus with mixed egg-yolk phosphatidylcholine/cholesterol liposomes has been investigated using the intrinsic tryptophan fluorescence emission (ITFE) signal. The ITFE intensity of alpha-hemolysin, which was obtained using a novel purification protocol, showed a triphasic increase on incubation with liposomes at low protein/lipid ratios. The first, rapid phase results in an increase in ITFE of 10%, which reflects rapid conformation changes in the alpha-hemolysin on association with the liposome membrane. The second phase of the ITFE increase is associated with a red shift from 334 to 339 nm in the maximum emission wavelength, suggesting the transition to a partially unfolded intermediate in the oligomerization process. The third phase of the ITFE intensity change demonstrates a temporal correlation with the appearance of SDS-stable oligomers. The results demonstrate the feasibility of identification of intermediate protein conformations in complex membrane-associated processes by manipulation of the liposomal membrane composition.
authors.affiliation: Department of Physics, IBILCE/UNESP, São José do Rio Preto, SP, Brazil.
authors.forename: R K
authors.initials: RK
authors.lastname: Bortoleto
authors.forename: A H
authors.initials: AH
authors.lastname: de Oliveira
authors.forename: R
authors.initials: R
authors.lastname: Ruller
authors.forename: R K
authors.initials: RK
authors.lastname: Arni
authors.forename: R J
authors.initials: RJ
authors.lastname: Ward
mesh_terms: D001427:Bacterial Toxins / Q000737:chemistry* / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism; D002852:Chromatography, Ion Exchange; D002942:Circular Dichroism; D005453:Fluorescence; D006460:Hemolysin Proteins / Q000737:chemistry* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008081:Liposomes / Q000378:metabolism*; D046911:Macromolecular Substances; D010713:Phosphatidylcholines / Q000378:metabolism; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D013050:Spectrometry, Fluorescence; D013211:Staphylococcus aureus / Q000737:chemistry*; D014364:Tryptophan / Q000737:chemistry
chemical_list: D001427:Bacterial Toxins; D006460:Hemolysin Proteins; D008081:Liposomes; D046911:Macromolecular Substances; D010713:Phosphatidylcholines; C021091:staphylococcal alpha-toxin; D014364:Tryptophan; D002784:Cholesterol