AI Article Synopsis
- Type VI secretion systems (T6SSs) enable bacteria like Salmonella to inject toxic proteins, known as effectors, into rival bacteria, impacting their growth and viability.
- The study focuses on the T6SS effector Tlde1, which disrupts target cells by damaging their cell structure and function, and can be neutralized by its related immunity protein Tldi1.
- Tlde1 shows enzymatic activity similar to l,d-transpeptidases, suggesting it cleaves essential components of the bacterial cell wall, and its homologs are widely found in various Proteobacteria, indicating a common strategy for bacterial competition.
Article Abstract
Type VI secretion systems (T6SSs) are nanomachines used by bacteria to inject toxic effectors into competitors. The identity and mechanism of many effectors remain unknown. We characterized a Salmonella T6SS antibacterial effector called Tlde1 that is toxic in target-cell periplasm and is neutralized by its cognate immunity protein (Tldi1). Microscopy analysis reveals that cells expressing Tlde1 stop dividing and lose cell envelope integrity. Bioinformatic analysis uncovers similarities between Tlde1 and the catalytic domain of l,d-transpeptidases. Point mutations on conserved catalytic residues abrogate toxicity. Biochemical assays reveal that Tlde1 displays both l,d-carboxypeptidase activity by cleaving peptidoglycan tetrapeptides between meso-diaminopimelic acid and d-alanine and l,d-transpeptidase exchange activity by replacing d-alanine by a non-canonical d-amino acid. Phylogenetic analysis shows that Tlde1 homologs constitute a family of T6SS-associated effectors broadly distributed among Proteobacteria. This work expands our current knowledge about bacterial effectors used in interbacterial competition and reveals a different mechanism of bacterial antagonism.
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| http://dx.doi.org/10.1016/j.celrep.2020.107813 | DOI Listing |
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