Tsitrin, Y.Morton, C. J.el-Bez, C.Paumard, P.Velluz, M. C.Adrian, M.Dubochet, J.Parker, M. W.Lanzavecchia, S.van der Goot, F. G.2009-01-302009-01-302009-01-30200210.1038/nsb839https://infoscience.epfl.ch/handle/20.500.14299/34626Proteins 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.Aeromonas hydrophilaBacterial Toxins/chemistry/*genetics/metabolismMembrane Proteins/chemistry/genetics/metabolism*Point MutationPore Forming Cytotoxic ProteinsProtein StructureQuaternaryProtein StructureTertiarySolubilitytext::journal::journal article::research article