Automated Bracket Assembly (Auto-Bracket) First, we designed a bracket assembly algorithm that converts an initial protein sequence to a feasible bracket by making gradual changes to the bracket notation text. This process is essentially a retrosynthetic analysis from the final ligation backward (i.e., upward). When a ligation junction is chosen, the two starting segments are assessed and sequence modifications are applied when necessary. With standard NCL chemistry, these include a) protection of Nterminal Cys in left-half segments to avoid cyclization and oligomerization, b) thiolation of any aa other than Cys at ligation sites (e.g., substitution of Ala with Cys or of Val with penicillamine