title: Conversion of a transmembrane to a water-soluble protein complex by a single point mutation.
abstract: Proteins exist in one of two generally incompatible states: either membrane associated or soluble. Pore-forming proteins are exceptional because they are synthesized as a water-soluble molecule but end up being located in the membrane -- that is, they are nonconstitutive membrane proteins. Here we report the pronounced effect of the single point mutation Y221G of the pore-forming toxin aerolysin. This mutation blocks the hemolytic activity of the toxin but does not affect its initial structure, its ability to bind to cell-surface receptors or its capacity to form heptamers, which constitute the channel-forming unit. The overall structure of the Y221G protein as analyzed by cryo-negative staining EM and three-dimensional reconstruction is remarkably similar to that of the wild type heptamer. The mutant protein forms a mushroom-shaped complex whose stem domain is thought to be within the membrane in the wild type toxin. In contrast to the wild type heptamer, which is a hydrophobic complex, the Y221G heptamer is fully hydrophilic. This point mutation has, therefore, converted a normally membrane-embedded toxin into a soluble complex.
authors.affiliation: Department of Genetics and Microbiology, University of Geneva, 1 rue Michel Servet, 1211 Geneva, Switzerland.
authors.forename: Yulia
authors.initials: Y
authors.lastname: Tsitrin
authors.forename: Craig J
authors.initials: CJ
authors.lastname: Morton
authors.forename: Catherine
authors.initials: C
authors.lastname: el-Bez
authors.forename: Patrick
authors.initials: P
authors.lastname: Paumard
authors.forename: Marie-Claire
authors.initials: MC
authors.lastname: Velluz
authors.forename: Marc
authors.initials: M
authors.lastname: Adrian
authors.forename: Jacques
authors.initials: J
authors.lastname: Dubochet
authors.forename: Michael W
authors.initials: MW
authors.lastname: Parker
authors.forename: Salvatore
authors.initials: S
authors.lastname: Lanzavecchia
authors.forename: F G
authors.initials: FG
authors.lastname: van der Goot
mesh_terms: D016980:Aeromonas hydrophila; D001427:Bacterial Toxins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017354:Point Mutation; D052899:Pore Forming Cytotoxic Proteins; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D012995:Solubility
chemical_list: D001427:Bacterial Toxins; D008565:Membrane Proteins; D052899:Pore Forming Cytotoxic Proteins; C107096:proaerolysin; C032676:aerolysin