Ribosomal Translation

Non-Ribosomal Peptide Synthesis (NRPS)

Summary

NRPS is a microbial enzymatic system that constructs complex peptides without mRNA templates or ribosomes. Modular megasynthetases follow a colinear logic where module order determines peptide sequence.

Key Points

  • 1No mRNA template—enzyme modules specify sequence
  • 2A domain selects amino acids; T domain carries them; C domain forms bonds
  • 3Can incorporate non-proteinogenic amino acids and D-isomers
  • 4Produces penicillin, vancomycin, cyclosporine, and many other drugs

Non-ribosomal peptide synthesis represents an alternative paradigm for peptide assembly, producing many of our most important natural product drugs.

Overview

NRPS produces peptides without:

  • mRNA templates
  • Ribosomes
  • tRNA

    • Instead, large megasynthetase enzymes directly specify and assemble the peptide sequence.

    Modular Architecture

    NRPS enzymes are organized into modules, each responsible for one amino acid:

    Core Domains

    Adenylation (A) Domain

  • Recognizes and activates a specific amino acid
  • Forms aminoacyl-adenylate intermediate
  • Determines substrate specificity
  • "Gatekeeping" domain

    • Thiolation (T) / Peptidyl Carrier Protein (PCP) Domain

  • Carries activated substrates and intermediates

    • - Uses phosphopantetheine arm as tether

  • Activated substrates attached via thioester bonds

    • Condensation (C) Domain

  • Catalyzes peptide bond formation
  • Joins amino acid from upstream T domain to downstream T domain
  • Some C domains have selectivity for stereochemistry

    • Accessory Domains

    - Epimerization (E): Converts L to D amino acids

    - Methylation (M): N- or C-methylation

    - Cyclization (Cy): Forms heterocyclic rings

    - Oxidation (Ox): Oxidizes thiazoline to thiazole

    Termination

    Thioesterase (TE) Domain

  • Releases the final product
  • Often cyclizes the peptide via macrolactonization/macrolactamization
  • Critical for product bioactivity

    • The Colinearity Rule

    A key principle: the order of modules in the megasynthetase directly determines the sequence of the peptide product.

    This modularity makes NRPS:

  • Predictable
  • Engineerable (in principle)
  • Evolvable

    • Chemical Diversity

    NRPS produces remarkable chemical diversity:

    Non-proteinogenic substrates:

  • D-amino acids
  • β-amino acids
  • Fatty acids
  • Hydroxy acids

    • Modifications:

  • Heterocyclization
  • Glycosylation
  • Halogenation
  • Macrocyclization

    • Important NRPS Products

    Many critical drugs are NRPS products:

    - Penicillin: β-lactam antibiotic

    - Vancomycin: Glycopeptide antibiotic

    - Cyclosporine: Immunosuppressant

    - Daptomycin: Lipopeptide antibiotic

    - Bleomycin: Anticancer agent

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