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Mutants were identified phenotypically by radial passive immune haemolysis assays and genotypically by colony hybridization with specific oligonucleotide probes. Mutant CT\u2010B poly\u2010peptides were characterized for immunoreactivity, binding to ganglioside GM1, ability to associate with the A subunit, ability to form holotoxin, and biological activity. Amino acid substitutions that caused decreased binding of mutant CT\u2010B to ganglioside GM1 and abolished toxicity included negatively charged or large hydrophobic residues for Gly\u201033 and negatively or positively charged residues for Trp\u201088. Substitution of lysine or arginine for Gly\u201033 did not affect immunoreactivity or GM1 \u2010binding activity of CT\u2010B but abolished or reduced toxicity of the mutant holotoxins, respectively. Substitutions of Glu or Asp for Arg\u201035 interfered with formation of holotoxin, but none of the observed substitutions for Lys\u201034 or Arg\u201035 affected binding of CT\u2010B to GM1. The Cys\u20109, Cys\u201086 and Trp\u201088 residues were important for establishing or maintaining the native conformation of CT\u2010B or protecting the CT\u2010B polypeptide from rapid degradation <jats:italic>in vivo.<\/jats:italic><\/jats:p>","DOI":"10.1111\/j.1365-2958.1991.tb01925.x","type":"journal-article","created":{"date-parts":[[2006,10,27]],"date-time":"2006-10-27T22:11:40Z","timestamp":1161987100000},"page":"1755-1767","source":"Crossref","is-referenced-by-count":71,"title":["Analysis of structure and function of the B subunit of cholera toxin by the use of site\u2010directed mutagenesis"],"prefix":"10.1111","volume":"5","author":[{"given":"M. G.","family":"Jobling","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"R. 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