title: Instability of toxin A subunit of AB(5) toxins in the bacterial periplasm caused by deficiency of their cognate B subunits.
abstract: Shiga toxin (STx) belongs to the AB(5) toxin family and is transiently localized in the periplasm before secretion into the extracellular milieu. While producing outer membrane vesicles (OMVs) containing only A subunit of the toxin (STxA), we created specific STx1B- and STx2B-deficient mutants of E. coli O157:H7. Surprisingly, STxA subunit was absent in the OMVs and periplasm of the STxB-deficient mutants. In parallel, the A subunit of heat-labile toxin (LT) of enterotoxigenic E. coli (ETEC) was absent in the periplasm of the LT-B-deficient mutant, suggesting that instability of toxin A subunit in the absence of the B subunit is a common phenomenon in the AB(5) bacterial toxins. Moreover, STx2A was barely detectable in the periplasm of E. coli JM109 when stx2A was overexpressed alone, while it was stably present when stxB was co-expressed. Compared with STx2 holotoxin, purified STx2A was degraded rapidly by periplasmic proteases when assessed for in vitro proteolytic susceptibility, suggesting that the B subunit contributes to stability of the toxin A subunit in the periplasm. We propose a novel role for toxin B subunits of AB(5) toxins in protection of the A subunit from proteolysis during holotoxin assembly in the periplasm.
authors.affiliation: The National Primate Research Center, Korea Research Institute of Bioscience and Biotechnology, Ochang, Cheongwon, Chungbuk 363-883, Republic of Korea.
authors.forename: Sang-Hyun
authors.initials: SH
authors.lastname: Kim
authors.forename: Su Hyang
authors.initials: SH
authors.lastname: Ryu
authors.forename: Sang-Ho
authors.initials: SH
authors.lastname: Lee
authors.forename: Yong-Hoon
authors.initials: YH
authors.lastname: Lee
authors.forename: Sang-Rae
authors.initials: SR
authors.lastname: Lee
authors.forename: Jae-Won
authors.initials: JW
authors.lastname: Huh
authors.forename: Sun-Uk
authors.initials: SU
authors.lastname: Kim
authors.forename: Ekyune
authors.initials: E
authors.lastname: Kim
authors.forename: Sunghyun
authors.initials: S
authors.lastname: Kim
authors.forename: Sangyong
authors.initials: S
authors.lastname: Jon
authors.forename: Russell E
authors.initials: RE
authors.lastname: Bishop
authors.forename: Kyu-Tae
authors.initials: KT
authors.lastname: Chang
mesh_terms: D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D017931:DNA Primers; D005816:Genetic Complementation Test; D006868:Hydrolysis; D046529:Microscopy, Electron, Transmission; D009154:Mutation; D019897:Periplasm / Q000378:metabolism*
chemical_list: D001427:Bacterial Toxins; D017931:DNA Primers