Cleavage Methodology

Natural product discovery has been at the root of modern drug design, and it continues to play a vital role as there is renewed focus on orally available peptide therapeutics. In particular, macrocyclic peptides often exhibit desirable characteristics such as high receptor-binding activity and specificity, metabolic stability, and cell permeability.

Examples of uniquely structured bioactive peptides with exceptional stability are cyclosporine-A, an immunosuppressant whose structure is rich in N-methylation, microcin J25, an antibacterial lasso peptide, and kalata-B1, a cyclotide with insecticidal activity. However, discovery efforts have been hindered in part by sequencing difficulties.

In work published in Angewandte Chemie, Intl.Ed., researchers in the Raj Group report a simple chemical sequencing method that overcomes the challenges of existing analytical techniques for highly stable macrocyclic and lasso peptides.

This site-selective cleavage methodology is applicable to peptides containing Ser, Thr, Cys, or Glu residues, due to their ability to form a cyclic urethane-derived moiety that is susceptible to cleavage, see figure. These residues are present in approximately 60% of naturally occurring macrocyclic peptides and 66% of lasso peptides as determined by a survey of NORINE, a cyclic peptide database, and a comprehensive list of all lasso peptides discovered to date.

This method is also applicable to several less common amino acids found in nonribosomal peptides containing reactive β- or γ-hydroxyl side chains, such as β-hydroxylphenylalanine and homoserine.

Ultimately, this chemical cleavage method will provide a generic approach for synthesizing interlocking peptides that could be used to make peptide-based supramolecular structures such as [2]catenanes, peptide daisy chains, and quasi‐catenanes from lasso scaffolds. Work in this direction is currently underway in the Raj laboratory.

Cyclic and Lasso Peptides: Sequence Determination, Topology Analysis, and Rotaxane Formation
Hader E. Elashal, Ryan D. Cohen, Heidi E. Elashal, Dr. Chuhan Zong, Prof. Dr. A. James Link, Prof. Dr. Monika Raj
Angew. Chemie, Intl. Ed., Volume57, Issue 21, May 22, 2018, Pages 6150-6154