Sandbox WWC6: Difference between revisions
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==Structure== | ==Structure== | ||
Hemolysins have three structural variations: alpha, beta, and gamma. These hemolysin types are comprised of di-, hepta- or octomeric subunits. | Hemolysins have three structural variations: alpha, beta, and gamma. These hemolysin types are comprised of di-, hepta- or octomeric subunits. | ||
===Alpha-hemolysin=== | ===Alpha-hemolysin=== | ||
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<scene name='69/696302/Alpha-hemolysin/1'>Alpha-hemolysin</scene> | <scene name='69/696302/Alpha-hemolysin/1'>Alpha-hemolysin</scene> | ||
Alpha hemolysins cause a partial lysis of red blood cells. | Alpha hemolysins cause a partial lysis of red blood cells. The heptameric pore assembles from water-soluble subunits. The alpha subunit, depicted right, consists seven identical monomeric units that exhibit rotational symmetry in oligomerized form. Each distinct subunit is differently colored for easy identification. The beta-barrel transmembrane domain is 50 Å in length <ref>http://www.ks.uiuc.edu/Research/hemolysin/<ref>. | ||
The heptameric pore assembles from water-soluble subunits The | |||
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==Mechanism | ==Mechanism== | ||
Four of each of the two subunits assemble in an alternating, circular pattern in the γ-HL pore, whereas seven distinct α-HL protomers assemble in a circular arrangement in the α-HL pore. These typically are comprised of three domains: the cap, rim and stem domains, named for the structural resemblance to a mushroom. The cap domain contains β-sandwiches from each protomer, while just below, the rim domain contains four looping β-strands. The stem domain takes on the antiparallel β-barrel, a portion of which becomes the transmembrane structure. | Four of each of the two subunits assemble in an alternating, circular pattern in the γ-HL pore, whereas seven distinct α-HL protomers assemble in a circular arrangement in the α-HL pore. These typically are comprised of three domains: the cap, rim and stem domains, named for the structural resemblance to a mushroom. The cap domain contains β-sandwiches from each protomer, while just below, the rim domain contains four looping β-strands. The stem domain takes on the antiparallel β-barrel, a portion of which becomes the transmembrane structure. | ||
===Pore formation=== | ===Pore formation=== | ||
Pore formation of hemolysins is believed to be a conserved process accross subtypes <ref>http://www.nature.com/ncomms/2014/140929/ncomms5897/full/ncomms5897.html<ref> | |||
Studies suggest that pore formation is achieved through a nonlytic intermediate oligomer, known as a prepore. The prepore model proposal suggests that the monomeric components assemble on the cell membrane surfacte into a prepore with prestem subunits packed inside. The formed prepore then goes through a conformational change prestem, forming the β-barrel pore. Several issues with the proposed pore formation mechanism have been identified including steric hindrance of the packed prestem structure. | Studies suggest that pore formation is achieved through a nonlytic intermediate oligomer, known as a prepore. The prepore model proposal suggests that the monomeric components assemble on the cell membrane surfacte into a prepore with prestem subunits packed inside. The formed prepore then goes through a conformational change prestem, forming the β-barrel pore. Several issues with the proposed pore formation mechanism have been identified including steric hindrance of the packed prestem structure. | ||