Meropenem inhibits D,D-carboxypeptidase activity in Mycobacterium tuberculosis

Mol Microbiol. 2012 Oct;86(2):367-81. doi: 10.1111/j.1365-2958.2012.08199.x. Epub 2012 Aug 28.


Carbapenems such as meropenem are being investigated for their potential therapeutic utility against highly drug-resistant tuberculosis. These β-lactams target the transpeptidases that introduce interpeptide cross-links into bacterial peptidoglycan thereby controlling rigidity of the bacterial envelope. Treatment of Mycobacterium tuberculosis (Mtb) with the β-lactamase inhibitor clavulanate together with meropenem resulted in rapid, polar, cell lysis releasing cytoplasmic contents. In Mtb it has been previously demonstrated that 3-3 cross-linkages [involving two diaminopimelate (DAP) molecules] predominate over 4-3 cross-linkages (involving one DAP and one D-alanine) in stationary-phase cells. We purified and analysed peptidoglycan from Mtb and found that 3-3 cross-linkages predominate throughout all growth phases and the ratio of 4-3/3-3 linkages does not vary significantly under any growth condition. Meropenem treatment was accompanied by a dramatic accumulation of unlinked pentapeptide stems with no change in the tetrapeptide pools, suggesting that meropenem inhibits both a D,D-carboxypeptidase and an L,D-transpeptidase. We purified a candidate D,D-carboxypeptidase DacB2 and showed that meropenem indeed directly inhibits this enzyme by forming a stable adduct at the enzyme active site. These results suggest that the rapid lysis of meropenem-treated cells is the result of synergistically inhibiting the transpeptidases that introduce 3,3-cross-links while simultaneously limiting the pool of available substrates available for cross-linking.

Publication types

  • Research Support, N.I.H., Intramural

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • Bacterial Proteins / antagonists & inhibitors
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Down-Regulation / drug effects*
  • Humans
  • Meropenem
  • Mycobacterium tuberculosis / drug effects*
  • Mycobacterium tuberculosis / enzymology*
  • Mycobacterium tuberculosis / genetics
  • Serine-Type D-Ala-D-Ala Carboxypeptidase / antagonists & inhibitors
  • Serine-Type D-Ala-D-Ala Carboxypeptidase / genetics
  • Serine-Type D-Ala-D-Ala Carboxypeptidase / metabolism*
  • Thienamycins / pharmacology*


  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Thienamycins
  • Serine-Type D-Ala-D-Ala Carboxypeptidase
  • Meropenem