title: A stability transition at mildly acidic pH in the alpha-hemolysin (alpha-toxin) from Staphylococcus aureus.
abstract: The effects of mildly acidic conditions on the free energy of unfolding (DeltaG(u)(buff)) of the pore-forming alpha-hemolysin (alphaHL) from Staphylococcus aureus were assessed between pH 5.0 and 7.5 by measuring intrinsic tryptophan fluorescence, circular dichroism and elution time in size exclusion chromatography during urea denaturation. Decreasing the pH from 7.0 to 5.0 reduced the calculated DeltaG(u)(buff) from 8.9 to 4.2 kcal mol(-1), which correlates with an increased rate of pore formation previously observed over the same pH range. It is proposed that the lowered surface pH of biological membranes reduces the stability of alphaHL thereby modulating the rate of pore formation.
authors.affiliation: Department of Physics, IBILCE/UNESP, Rua Cristovão Colombo 2265, São José do Rio Preto, SP, Brazil.
authors.forename: R K
authors.initials: RK
authors.lastname: Bortoleto
authors.forename: R J
authors.initials: RJ
authors.lastname: Ward
mesh_terms: D002850:Chromatography, Gel; D002942:Circular Dichroism; D005453:Fluorescence; D006863:Hydrogen-Ion Concentration; D011489:Protein Denaturation; D013211:Staphylococcus aureus / Q000378:metabolism*; D013816:Thermodynamics; D014364:Tryptophan / Q000737:chemistry; D010738:Type C Phospholipases / Q000737:chemistry / Q000378:metabolism*; D014508:Urea / Q000737:chemistry
chemical_list: D014364:Tryptophan; D014508:Urea; D010738:Type C Phospholipases