TssB

TssB is a protein component of the Type VI secretion system (T6SS) found in various bacteria. The T6SS is a complex molecular machine that bacteria use to directly inject effector proteins into neighboring cells, which can include other bacteria, eukaryotic cells, or archaea. TssB is known to be an essential structural component of the T6SS apparatus, playing a crucial role in its assembly and function.

Specifically, TssB is a protein that forms part of the contractile sheath surrounding the TssE (or baseplate) and TssF/TssG (or inner tube) structures. This sheath is analogous to the contractile sheath of bacteriophages and is responsible for generating the force needed to propel the inner tube and its associated effector cargo out of the bacterial cell. TssB subunits polymerize to form this sheath, which undergoes a rapid contraction during T6SS activation. Without functional TssB, the T6SS sheath cannot form properly, rendering the secretion system inactive. Genetic studies have consistently shown that mutations in the tssB gene abolish T6SS-mediated immunity or inter-bacterial killing. Its precise assembly mechanism and interactions with other T6SS components are areas of ongoing research.