Structure AB5 toxin

general diagram of subunit of ab5 toxin disulfide linkage.



ribbon diagram of b-subunit of cholera toxin.


a subunit

the subunit of ab5 toxin portion responsible catalysis of specific targets. shiga toxin family, subunit hosts trypsin-sensitive region gives out 2 fragmented domains when cleaved. region has not been confirmed other ab5 toxin families yet. in general, 2 domains of subunit, named a1 , a2, linked disulfide bond. domain a1 (approximately 22kda in cholera toxin or heat labile enterotoxins) part of toxin responsible toxic effects. domain a2 (approximately 5kda in cholera toxin or heat labile enterotoxin) provides non-covalent linkage b subunit through b subunit s central pore. a1 chain cholera toxin catalyzes transfer of adp-ribose nicotinamide adenine dinucleotide(nad) arginine or other guanidine compounds utilizing adp-ribosylation factors (arfs). in absence of arginine or simple guanidino compounds, toxin mediated nad+ nucleosidase (nadase) activity proceeds using water nucleophile.

b subunit

the b subunits form five-membered or pentameric ring, 1 end of subunit goes , held. b subunit ring capable of binding receptor on surface of host cell. without b subunits, subunit has no way of attaching or entering cell, , no way exert toxic effect. cholera toxin, shiga toxin, , subab toxin have b subunits made of 5 identical protein components, meaning b subunits homopentamers. pertussis toxin different pentameric ring made of 4 different protein components, 1 of components repeated form heteropentamer.