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. 2014 May;80(9):2928–2940. doi: 10.1128/AEM.04058-13

FIG 4.

FIG 4

(A) MS/MS data for the B subunit (disulfide bond intact) of Stx2 of E. coli O104:H4 (German outbreak strain). The mature amino acid sequence is provided above the spectrum. An asterisk indicates a site of polypeptide backbone fragmentation, and the ion type/number is provided above or below the sequence. A fragment ion with a ψ superscript indicates the presence of a fragment ion triplet that is due to fragmentation of the polypeptide backbone between the two cysteine residues involved in a disulfide bond and symmetric and asymmetric cleavage of the disulfide bond. (B) MS/MS data for the B subunit (disulfide bond reduced) of Stx2 of E. coli O104:H4. The mature amino acid sequence is provided above. An asterisk indicates a site of polypeptide backbone fragmentation, and the ion type/number is provided above or below the sequence. Note that there are no fragment ion triplets as the disulfide bond is now reduced.