How the MccB bacterial ancestor of ubiquitin E1 initiates biosynthesis of the microcin C7 antibiotic

EMBO J. 2009 Jul 8;28(13):1953-64. doi: 10.1038/emboj.2009.146. Epub 2009 Jun 4.


The 39-kDa Escherichia coli enzyme MccB catalyses a remarkable posttranslational modification of the MccA heptapeptide during the biosynthesis of microcin C7 (MccC7), a 'Trojan horse' antibiotic. The approximately 260-residue C-terminal region of MccB is homologous to ubiquitin-like protein (UBL) activating enzyme (E1) adenylation domains. Accordingly, MccB-catalysed C-terminal MccA-acyl-adenylation is reminiscent of the E1-catalysed activation reaction. However, unlike E1 substrates, which are UBLs with a C-terminal di-glycine sequence, MccB's substrate, MccA, is a short peptide with an essential C-terminal Asn. Furthermore, after an intramolecular rearrangement of MccA-acyl-adenylate, MccB catalyses a second, unique reaction, producing a stable phosphoramidate-linked analogue of acyl-adenylated aspartic acid. We report six-crystal structures of MccB in apo, substrate-, intermediate-, and inhibitor-bound forms. Structural and kinetic analyses reveal a novel-peptide clamping mechanism for MccB binding to heptapeptide substrates and a dynamic-active site for catalysing dual adenosine triphosphate-consuming reactions. The results provide insight into how a distinctive member of the E1 superfamily carries out two-step activation for generating the peptidyl-antibiotic MccC7.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Anti-Bacterial Agents / biosynthesis
  • Aspartic Acid / analogs & derivatives
  • Aspartic Acid / metabolism
  • Bacteriocins / biosynthesis
  • Catalytic Domain
  • Crystallography, X-Ray
  • Escherichia coli / enzymology
  • Escherichia coli Proteins / chemistry*
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism*
  • Humans
  • Ligases / chemistry*
  • Ligases / genetics
  • Ligases / metabolism*
  • Models, Molecular
  • Molecular Sequence Data
  • Mutation
  • Nucleotides / chemistry
  • Nucleotides / metabolism
  • Peptides / chemistry*
  • Peptides / metabolism*
  • Protein Binding
  • Protein Conformation
  • Protein Processing, Post-Translational
  • Sequence Alignment
  • Ubiquitin-Activating Enzymes / genetics


  • Anti-Bacterial Agents
  • Bacteriocins
  • Escherichia coli Proteins
  • Nucleotides
  • Peptides
  • microcin
  • Aspartic Acid
  • Ligases
  • MccB protein, E coli
  • Ubiquitin-Activating Enzymes