PMID:22393043

Citation	Ma, LS, Narberhaus, F and Lai, EM (2012) IcmF family protein TssM exhibits ATPase activity and energizes type VI secretion. J. Biol. Chem. 287:15610-21
Abstract	The type VI secretion system (T6SS) with diversified functions is widely distributed in pathogenic Proteobacteria. The IcmF (intracellular multiplication protein F) family protein TssM is a conserved T6SS inner membrane protein. Despite the conservation of its Walker A nucleotide-binding motif, the NTPase activity of TssM and its role in T6SS remain obscure. In this study, we characterized TssM in the plant pathogen Agrobacterium tumefaciens and provided the first biochemical evidence for TssM exhibiting ATPase activity to power the secretion of the T6SS hallmark protein, hemolysin-coregulated protein (Hcp). Amino acid substitutions in the Walker A motif of TssM caused reduced ATP binding and hydrolysis activity. Importantly, we discovered the Walker B motif of TssM and demonstrated that it is critical for ATP hydrolysis activity. Protein-protein interaction studies and protease susceptibility assays indicated that TssM undergoes an ATP binding-induced conformational change and that subsequent ATP hydrolysis is crucial for recruiting Hcp to interact with the periplasmic domain of the TssM-interacting protein TssL (an IcmH/DotU family protein) into a ternary complex and mediating Hcp secretion. Our findings strongly argue that TssM functions as a T6SS energizer to recruit Hcp into the TssM-TssL inner membrane complex prior to Hcp secretion across the outer membrane.
Links	PubMed PMC3346141 Online version:10.1074/jbc.M111.301630
Keywords	Adenosine Triphosphatases/genetics; Adenosine Triphosphatases/metabolism; Adenosine Triphosphate/metabolism; Agrobacterium tumefaciens/genetics; Agrobacterium tumefaciens/metabolism; Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Cell Membrane/metabolism; Hydrolysis; Immunoblotting; Membrane Proteins/genetics; Membrane Proteins/metabolism; Models, Biological; Mutation; Protein Binding; Protein Transport; Spheroplasts/genetics; Spheroplasts/metabolism
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
AGRT5:A9CGF9		GO:0016887: ATPase activity	ECO:0000315:		F		Figure 1 and Figure 5 both show TssM ATPase activity based on mutations in the Walker A and B motifs	complete
AGRT5:A9CGF9		GO:0033104: type VI protein secretion system complex	ECO:0000315:		C		Figure 6 shows TssM is part of the type VI protein secretion system complex and aids in secretion of Hcp	complete

References

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