cyclic peptides generated by the widely used split-intein mediated circular ligation of peptides and proteins (SICLOPPS) strategy for binders of AβOs. These selections identified cyclo-CRLISFF, which significantly delayed Aβ42 aggregation in vitro but displayed a mechanism inconsistent with inhibitors selectively targeting AβOs. To resolve this discrepancy, we tested whether intermediates formed during SICLOPPS cyclic peptide generation might also possess AβO binding activity. Our experiments showed that the CRLISFF sequence was active as an intein-bound intermediate which selectively targeted AβOs by inhibiting the secondary nucleation step of the Aβ42 aggregation cascade. This intermediate has not been previously examined in studies employing SICLOPPS and may present a convoluting factor when using this technology to generate cyclic peptide libraries. The CRLISFF motif also retained activity when transplanted onto an unrelated protein scaffold, suggesting that SICLOPPS sequences may be compatible with peptide grafting strategies used to create protein-based binders.
Lee et al. (Wed,) studied this question.