title: Membrane insertion of Escherichia coli alpha-hemolysin is independent from membrane lysis.
abstract: Escherichia coli alpha-hemolysin (HlyA) is a protein exotoxin that binds and lyses eukaryotic cell and model membranes in the presence of calcium. Previous studies have been able to distinguish between reversible toxin binding to the membrane and irreversible insertion into the lipid matrix. Membrane lysis occurs as the combined effect of protein insertion plus a transient perturbation of the membrane bilayer structure. In the past, insertion and bilayer perturbation have not been experimentally dissected. This has now been achieved by studying HlyA penetration into lipid monolayers at the air-water interface, in which three-dimensional effects (of the kind required to break down the bilayer permeability barrier) cannot occur. The study of native HlyA, together with the nonlytic precursor pro-HlyA, and of different mutants demonstrates that although some nonlytic variants (e.g. pro-HlyA) exhibit very low levels of insertion, others (e.g. the nonlytic mutant HlyA H859N) insert even more strongly than the lytic wild type. These results show that insertion does not necessarily lead to membrane lysis, i.e. that insertion and lysis are not "coupled" phenomena. Millimolar levels of Ca(2+), which are essential for the lytic activity, cause an extra degree of insertion but only in the case of the lytic forms of HlyA.
authors.affiliation: Unidad de Biofísica (Consejo Superior de Investigaciones Científicas, Universidad del País Vasco/Euskal Herriko Unibertsitatea), and Departamento de Bioquímica, Universidad del País Vasco, Aptdo. 644, 48080 Bilbao, Spain.
authors.forename: Lissete
authors.initials: L
authors.lastname: Sánchez-Magraner
authors.forename: Aitziber L
authors.initials: AL
authors.lastname: Cortajarena
authors.forename: Félix M
authors.initials: FM
authors.lastname: Goñi
authors.forename: Helena
authors.initials: H
authors.lastname: Ostolaza
mesh_terms: D000327:Adsorption; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D006460:Hemolysin Proteins / Q000235:genetics / Q000378:metabolism*; D008055:Lipids / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D006460:Hemolysin Proteins; C036507:Hlya protein, E coli; D008055:Lipids; D008081:Liposomes; D002118:Calcium