Halogenation of Peptides and Proteins Using Engineered Tryptophan Halogenase Enzymes

Recent Advances in Augmenting the Therapeutic Efficacy of Peptide-Drug Conjugates

There is an urgent need for the development of safe and effective modalities for the treatment of diseases owing to drug resistance, undesired side effects, and poor clinical outcomes. Combining cell-targeting and efficient cell-killing properties, peptide-drug conjugates (PDCs) have demonstrated superior efficacy compared with peptides and payloads alone. However, innovative molecular designs of PDCs are essential for further improving targeting precision, protease resistance and stability, cell permeability, and overall treatment efficacy. Several strategies have been developed to address these challenges, such as multivalency approaches, bispecific targeting, and long-acting PDCs. Other novel strategies, including overcoming biological barriers, conjugating novel functional payloads, and targeting macropinocytosis, have also shown promise. This perspective compiles the most recent strategies for enhancing PDC treatment efficacy, highlights key advancements in PDC, and provides insights on future directions for the development of novel PDCs.

Coupling and regulation mechanisms of the flavin-dependent halogenase PyrH observed by infrared difference spectroscopy

Flavin-dependent halogenases are central enzymes in the production of halogenated secondary metabolites in various organisms and they constitute highly promising biocatalysts for regioselective halogenation. The mechanism of these monooxygenases includes formation of hypohalous acid from a reaction of fully reduced flavin with oxygen and halide. The hypohalous acid then diffuses via a tunnel to the substrate-binding site for halogenation of tryptophan and other substrates. Oxidized flavin needs to be reduced for regeneration of the enzyme, which can be performed in vitro by a photoreduction with blue light. Here, we employed this photoreduction to study characteristic structural changes associated with the transition from oxidized to fully reduced flavin in PyrH from Streptomyces rugosporus as a model for tryptophan-5-halogenases. The effect of the presence of bromide and chloride or the absence of any halides on the UV-vis spectrum of the enzyme demonstrated a halide-dependent structure of the flavin-binding pocket. Light-induced FTIR difference spectroscopy was applied and the signals assigned by selective isotope labeling of the protein moiety. The identified structural changes in α-helix and β-sheet elements were strongly dependent on the presence of bromide, chloride, the substrate tryptophan, and the product 5-chloro-tryptophan, respectively. We identified a clear allosteric coupling in solution at ambient conditions between cofactor-binding site and substrate-binding site that is active in both directions, despite their separation by a tunnel. We suggest that this coupling constitutes a fine-tuned mechanism for the promotion of the enzymatic reaction of flavin-dependent halogenases in dependence of halide and substrate availability.

Recent advances in the development of therapeutic peptides

Peptides have unique characteristics that make them highly desirable as therapeutic agents. The physicochemical and proteolytic stability profiles determine the therapeutic potential of peptides. Multiple strategies to enhance the therapeutic profile of peptides have emerged. They include chemical modifications, such as cyclization, substitution with d-amino acids, peptoid formation, N-methylation, and side-chain halogenation, and incorporation in delivery systems. There have been recent advances in approaches to discover peptides having these modifications to attain desirable therapeutic properties. We critically review these recent advancements in therapeutic peptide development.