title: The properties of Bacillus cereus hemolysin II pores depend on environmental conditions.
abstract: Hemolysin II (HlyII), one of several cytolytic proteins encoded by the opportunistic human pathogen Bacillus cereus, is a member of the family of oligomeric beta-barrel pore-forming toxins. This work has studied the pore-forming properties of HlyII using a number of biochemical and biophysical approaches. According to electron microscopy, HlyII protein interacts with liposomes to form ordered heptamer-like macromolecular assemblies with an inner pore diameter of 1.5-2 nm and an outer diameter of 6-8 nm. This is consistent with inner pore diameter obtained from osmotic protection assay. According to the 3D model obtained, seven HlyII monomers might form a pore, the outer size of which has been estimated to be slightly larger than by the other method, with an inner diameter changing from 1 to 4 nm along the channel length. The hemolysis rate has been found to be temperature-dependent, with an explicit lag at lower temperatures. Temperature jump experiments have indicated the pore structures formed at 37 degrees C and 4 degrees C to be different. The channels formed by HlyII are anion-selective in lipid bilayers and show a rising conductance as the salt concentration increases. The results presented show for the first time that at high salt concentration HlyII pores demonstrate voltage-induced gating observed at low negative potentials. Taken together we have found that the membrane-binding properties of hemolysin II as well as the properties of its pores strongly depend on environmental conditions. The study of the properties together with structural modeling allows a better understanding of channel functioning.
authors.affiliation: Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia.
authors.forename: Zhanna I
authors.initials: ZI
authors.lastname: Andreeva
authors.forename: Vladimir F
authors.initials: VF
authors.lastname: Nesterenko
authors.forename: Maria G
authors.initials: MG
authors.lastname: Fomkina
authors.forename: Vadim I
authors.initials: VI
authors.lastname: Ternovsky
authors.forename: Natalia E
authors.initials: NE
authors.lastname: Suzina
authors.forename: Anastasia Yu
authors.initials: AY
authors.lastname: Bakulina
authors.forename: Alexander S
authors.initials: AS
authors.lastname: Solonin
authors.forename: Elena V
authors.initials: EV
authors.lastname: Sineva
mesh_terms: D001409:Bacillus cereus / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D004594:Electrophysiology; D006460:Hemolysin Proteins / Q000737:chemistry / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism*; D008051:Lipid Bilayers / Q000378:metabolism*; D008081:Liposomes; D008560:Membrane Fluidity; D012492:Salts / Q000494:pharmacology; D013696:Temperature
chemical_list: C085361:ApxII toxin, bacteria; D001426:Bacterial Proteins; D006460:Hemolysin Proteins; D007473:Ion Channels; D008051:Lipid Bilayers; D008081:Liposomes; D012492:Salts