Identification of stapled BtPul variants. (A) SDS-PAGE of the wild-type (WT) and its variants. “Distance” refers to the number of amino acids between the components of the O2beY/Cys pair in the primary sequence. M represents the lane of the protein marker. (B) Q-TOF MS spectrum of the WT and its variants. Theoretical masses: T73(O2beY)-171C: 81821 Da for not cross-linked, 81739 Da for cross-linked; P95(O2beY)-E384C: 81799 Da for not cross-linked, 81717 Da for cross-linked; P135(O2beY)-A314C: 81857 Da for not cross-linked, 81775 Da for cross-linked; E162(O2beY)-Y317C: 81733 Da for not cross-linked, 81651 Da for cross-linked; G620(O2beY)-S216C: 81881 Da for not cross-linked, 81799 Da for cross-linked; W711(O2beY)-A699C: 81768 Da for not cross-linked, 81686 Da for cross-linked; C686(O2beY)-K553C: 81794 Da for not cross-linked, 81712 Da for cross-linked; F622(O2beY)-V712C: 81779 Da for not cross-linked, 81697 Da for cross-linked.