Structural basis for recognition of the type VI spike protein VgrG3 by a cognate immunity protein

• VgrG3C has inverting glycosyl hydrolase features adopting T4-lysozyme-like fold.
• Oligomeric TsaB may play an important role in biological functions.
• VgrG3C-TsaB complex exits as a heterotetramer in solution.
• TsaB inhibits VgrG3C through the molecular mimicry of its substrate.

The bacterial type VI secretion system (T6SS) is used by donor cells to inject toxic effectors into receptor cells. The donor cells produce the corresponding immunity proteins to protect themselves against the effector proteins, thereby preventing their self-intoxication. Recently, the C-terminal domain of VgrG3 was identified as a T6SS effector. Information on the molecular mechanism of VgrG3 and its immunity protein TsaB has been lacking. Here, we determined the crystal structures of native TsaB and the VgrG3C–TsaB complex. VgrG3C adopts a canonical phage-T4-lysozyme-like fold. TsaB interacts with VgrG3C through molecular mimicry, and inserts into the VgrG3C pocket.Structured summary of protein interactionsVgrG3 and TsaBbind by x-ray crystallography (View interaction)TsaB and TsaBbind by x-ray crystallography (View interaction)VgrG3 and TsaBbind by cosedimentation in solution (View interaction)TsaB and TsaBbind by cosedimentation in solution (1, 2)TsaBbinds to VgrG3 by surface plasmon resonance (1, 2, 3, 4, 5, 6, 7)VgrG3 and TsaBbind by molecular sieving (View interaction)TsaB and TsaBbind by molecular sieving (View interaction)VgrG3 and TsaBbind by x ray scattering (View interaction)