Figure 3.

(A,B) Protein sequence coverage in tryptic MS-MS analyses; (A) Linear Z3 protein and (B) cyclic Z3 protein. Each blue underline indicates one identified peptide sequence. The green box indicates the peptide sequence connecting the N and C termini of the cyclic Z3 protein. (C) Identification of ligation scar sequence in trypsin-digested cyclic Z3. MS/MS spectrum (after trypsin digestion) of the cyclic Z3 protein shows the junction sequence SGYSSSDVVDNK, which is not genetically encoded but is expected in the cyclic protein. The b and y ions corresponding to the ligation scar are shown.