Abstract
The incorporation of non-canonical amino acids (ncAA) is an elegant way for the chemical diversification of recombinantly produced antimicrobial peptides (AMPs). Residue- and site-specific installation methods in several bacterial production hosts hold great promise for the generation of new-to-nature AMPs, and can contribute to tackle the ongoing emergence of antibiotic resistance in pathogens. Especially from a pharmacological point of view, desirable improvements span pH and protease resistance, solubility, oral availability and circulation half-life. Although the primary focus of this report is on ribosomally synthesized and post-translationally modified peptides (RiPPs), we have included selected cases of peptides produced by solid phase peptide synthesis to comparatively show the potential and impact of ncAA introduction. Generally speaking, the introduction of ncAAs in recombinant AMPs delivers novel levels of chemical diversification. Cotranslationally incorporated, they can take part in AMP biogenesis either through direction interaction with elements of the post-translational modification (PTM) machinery or as untargeted sites with unique physicochemical properties and chemical handles for further modification. Together with genetic libraries, genome mining and processing by PTM machineries, ncAAs present not a mere addition to this process, but a highly diverse pool of building blocks to significantly broaden the chemical space of this valuable class of molecules. This perspective summarizes new developments of ncAA containing peptides. Challenges to be resolved in order to reach large-scale pharmaceutical production of these promising compounds and prospects for future developments are discussed.
Highlights
Constant isolation of new multidrug-resistant microbes affords a parallel development of new antimicrobial compounds for the treatment of infections
For recombinant peptide and protein production, two main methods enable the ribosomal incorporation of non-canonical amino acid (ncAA)
Pioneered by Schultz and coworkers, stop or quadruplet codon suppression constitutes the second option for ncAA incorporation (Wang et al, 2001; Anderson et al, 2004). o-pairs of a tRNA and a matching aminoacyl-tRNA synthetase (aaRS) enable the sitespecific installation of ncAAs
Summary
Constant isolation of new multidrug-resistant microbes affords a parallel development of new antimicrobial compounds for the treatment of infections. Development of novel antimicrobials employing modularization and alteration of genetic components (leader peptide, core and PTM genes) as well as genome mining have been reviewed recently (MontalbánLópez et al, 2016). Beyond the scope of this work, detailed information from more general as well as biomedical perspective including market potential, mode of action and production methods can be found in recent reviews (da Costa et al, 2015; Ageitos et al, 2016). As illustrated for nisin, RiPPs are initially produced as linear precursors composed of a leader and a core peptide region. Via three principal mechanisms (da Costa et al, 2015), many RiPPs exhibit significant inhibitory activity against Gram-positive bacteria, e.g., Streptococcus, Staphylococcus, and Bacillus (Arnison et al, 2013)
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