System for Peptide Macrocycle Synthesis

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Macrocycles are cyclic macromolecules that can exhibit drug-like physicochemical and pharmacokinetic properties, such as good membrane permeability, metabolic stability, and bioavailability. The intrinsic characteristics of macrocycles often lead to potent biological activities, allowing for prominent use in medicine. Macrocycle drugs are mostly natural products, or derivatives thereof, produced by organisms such as fungi or plants. Currently, about 70 macrocycle molecules have been developed for therapeutic purposes. Applications range from antibiotics, such as erythromycin, to immunosuppressants and hormones, such as cyclosporine and oxytocin, respectively. Success with naturally derived macrocycles have led many to the idea of performing drug screens with combinatorial libraries of synthetic marcocycles to identify new molecules which modulate activity of elusive therapeutic targets. Although many advances have been made in the design of combinatorial libraries for developing oral macrocycle drugs, technology for synthesizing the compounds is lagging. Head-to-tail cyclization of synthetic peptides is particularly challenging without the use of an enzyme. Identification of Butelase I, an asparagine/aspartate peptide ligase, greatly enhanced the range of peptides that could be enzymatically cyclized; however Butelase I is unable to cyclize peptides under 14 amino acids which imposes a size limitation on possible compounds.

Michigan State University has developed a system for producing small, monocyclic, bi-cyclic, or linear peptides as a source of new molecules for drug discovery and/or medical reagents. Compound libraries could consist of native genes from various fungi species, or sequences for specific, desired compounds could be synthesized and inserted between the conserved flanking regions for production. Large quantities of compounds could be produced by cloning desired genes into organisms that are easily manipulated, such as E. coli, offering a low-cost source of compounds to make large-scale applications economically feasible.

Fungi are a valuable source of biologically active hepta- and octapeptide macrocycle molecules. Macrocycle synthesis in fungi occurs in two steps. First, the gene encoding the macrocycle is translated as a proprotein of 34-35 amino acids. The proprotein contains conserved amino acid sequences flanking a “hypervariable region” which contains the respective macrocycle molecule. GmPOPB is an enzyme in the prolyl oligopeptidase (POP) subfamily that has been found to cleave the flanking regions from the hypervariable region and catalyze cyclization and release of an octapeptide macrocycle molecule.

Genes with the general structure of known macrocycles have been found throughout the genome, indicating that fungi have evolved a mechanism for generating a diverse collection of small peptides and perhaps have a larger capacity for generating macrocycle molecules than previously thought. This system further enhances synthetic peptide cyclization capabilities and could be harnessed to produce combinatorial libraries of small monocyclic, bicyclic, or linear peptides of any sequence.

Benefits

  • Cyclizes small peptides: able to cyclize peptides half the size required for Butelase I
  • Scalable: large quantities of compounds may be produced for research and/or biomedical applications
  • Low cost: production of compounds using E. coli is inexpensive as compared to de novo chemical synthesis
  • Simple: only requires general molecular biology techniques

Applications

  • Chemical libraries for discovery of new research or medical reagents
  • Chemical libraries for discovery of new therapeutics
  • Production of compounds for therapeutic or medical applications

PATENT STATUS: US application 12/268,229 US application 13/362,561

From MSU Today: A Poisonous Cure