Figure 3.

Scheme of the one-bead-one-compound (OBOC)-based approach to find a good nucleophile for the DegP-mediated transpeptidation. Beads are linked to the dipeptide library (X₁X₂) as well as Ni²⁺: NTA, of which the latter recruits the His-tagged DegP on beads. When the N-terminally biotinylated substrate is mixed with the above beads, beads with good nucleophiles may be covalently linked to the N-terminal fragment of the model peptide. The fusion enzyme of streptavidin and alkaline phosphatase binds to these biotinylated beads and the reaction with 5-bromo-4-chloro-3-indoyl-phosphate (BCIP) turns these beads blue.