Loss of a Functionally and Structurally Distinct ld-Transpeptidase, LdtMt5, Compromises Cell Wall Integrity in Mycobacterium tuberculosis

• Published in: The Journal of biological chemistry Vol. 290; no. 42; pp. 25670 - 25685
• Main Authors: Brammer Basta, Leighanne A., Ghosh, Anita, Pan, Ying, Jakoncic, Jean, Lloyd, Evan P., Townsend, Craig A., Lamichhane, Gyanu, Bianchet, Mario A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 16-10-2015; American Society for Biochemistry and Molecular Biology
• Subjects: Amino Acid Sequence; antibiotics; biosynthesis; Catalysis; Catalytic Domain; cell wall; Cell Wall - physiology; enzyme kinetics; enzyme structure; Enzymology; Hydrogen-Ion Concentration; Hydrolysis; Hydrophobic and Hydrophilic Interactions; Molecular Sequence Data; Mycobacterium tuberculosis; Mycobacterium tuberculosis - enzymology; Mycobacterium tuberculosis - metabolism; Mycobacterium tuberculosis - physiology; peptidoglycan; Peptidoglycan - metabolism; Peptidyl Transferases - chemistry; Peptidyl Transferases - genetics; Peptidyl Transferases - metabolism; Protein Conformation; Sequence Homology, Amino Acid; peptidoglycan; Mycobacterium tuberculosis; biosynthesis; cell wall; antibiotics; enzyme kinetics; enzyme structure
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M115.660753

The final step of peptidoglycan (PG) biosynthesis in bacteria involves cross-linking of peptide side chains. This step in Mycobacterium tuberculosis is catalyzed by ld- and dd-transpeptidases that generate 3→3 and 4→3 transpeptide linkages, respectively. M. tuberculosis PG is predominantly 3→3 cross-linked, and LdtMt2 is the dominant ld-transpeptidase. There are four additional sequence paralogs of LdtMt2 encoded by the genome of this pathogen, and the reason for this apparent redundancy is unknown. Here, we studied one of the paralogs, LdtMt5, and found it to be structurally and functionally distinct. The structures of apo-LdtMt5 and its meropenem adduct presented here demonstrate that, despite overall architectural similarity to LdtMt2, the LdtMt5 active site has marked differences. The presence of a structurally divergent catalytic site and a proline-rich C-terminal subdomain suggest that this protein may have a distinct role in PG metabolism, perhaps involving other cell wall-anchored proteins. Furthermore, M. tuberculosis lacking a functional copy of LdtMt5 displayed aberrant growth and was more susceptible to killing by crystal violet, osmotic shock, and select carbapenem antibiotics. Therefore, we conclude that LdtMt5 is not a functionally redundant ld-transpeptidase, but rather it serves a unique and important role in maintaining the integrity of the M. tuberculosis cell wall.
Background:M. tuberculosis LdtMt5 is an LdtMt2 paralog that cross-links peptidoglycan stem peptides.
Results: LdtMt5 is structurally divergent, strains lacking LdtMt5 are more susceptible to chemical and environmental stresses, and LdtMt2 cannot compensate for its loss.
Conclusion: LdtMt2 and LdtMt5 serve non-redundant roles in peptidoglycan maintenance.
Significance: LdtMt5 is necessary for properly maintaining cell wall integrity and should be pursued as a drug target.