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Biosynthetic tailoring of microcin E492m: post-translational modification affords an antibacterial

Elizabeth M Nolan1, Michael A Fischbach, Alexander Koglin

  • 1Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.

Journal of the American Chemical Society
|November 2, 2007
PubMed

Insights

Four proteins modify microcin E492 (MccE492), a toxin from Klebsiella pneumoniae. They attach a modified enterobactin (iron scavenger) to MccE492, creating a potent antibacterial agent.

Area of Science:

  • Microbiology
  • Biochemistry
  • Molecular Biology

Background:

  • Klebsiella pneumoniae RYC492 secretes microcin E492 (MccE492), an 84-residue protein toxin targeting Gram-negative bacteria.
  • MccE492 undergoes extensive post-translational modification to achieve its mature, active form, MccE492m.

Purpose of the Study:

  • To elucidate the molecular mechanisms and protein machinery responsible for the post-translational modification of MccE492.
  • To characterize the enzymatic steps involved in the derivatization of enterobactin and its subsequent attachment to MccE492.

Main Methods:

  • Genetic analysis of the MccE492 gene cluster to identify modifying proteins (MceCDIJ).
  • Biochemical assays to determine the enzymatic activities of MceC, MceD, MceI, and MceJ.
  • Characterization of the modified enterobactin and its linkage to MccE492 using analytical techniques.

Main Results:

  • The MceCDIJ protein complex is responsible for the post-translational tailoring of MccE492.
  • MceC and MceD enzymes modify enterobactin via C-glycosylation and hydrolysis.
  • MceI and MceJ complex attach the modified enterobactin to the C-terminus of MccE492, forming a C6' glycosyl ester linkage after nonenzymatic rearrangement.

Conclusions:

  • The MceCDIJ proteins are essential for producing the mature, toxic form of MccE492.
  • The study reveals a novel mechanism for siderophore conjugation to peptide toxins.
  • Understanding these modifications provides insights into bacterial toxin production and potential antimicrobial targets.

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