Assessing histidine tags for recruiting deoxyribozymes to catalyze peptide and protein modification reactions

We evaluate the ability of hexahistidine (His₆) tags on peptide and protein substrates to recruit deoxyribozymes for modifying those substrates. For two different deoxyribozymes, one that creates tyrosine-RNA nucleopeptides and another that phosphorylates tyrosine side chains, we find substantial improvements in yield, k_obs, and K_m for peptide substrates due to recruiting by His₆/Cu²⁺. However, the recruiting benefits of the histidine tag are not observed for larger protein substrates, likely because the tested deoxyribozymes either cannot access the target peptide segments or cannot function when these segments are presented in a structured protein context.