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Type VI secretion system, VipA, VC_A0107 or Hcp2 T6SSs are toxin delivery systems. It is a multiprotein complex requiring numerous core proteins (Tss proteins) including cytoplasmic, transmembrane, and outer membrane components. The needle or tube apparatus is comprised of a phage-like complex, similar to the T4 contractile bacteriophage tail, which is thought to be anchored to the membrane by a trans-envelope complex. VipA is a family of Gram-negative bacterial proteins that form part of the type VI pathogenic secretion system. Members have been variously defined as VC_A0107 family, Hcp2, TssB and VipA, for ClpV-interacting proteins. VipB and VipA proteins interact very closely to form the shaft of the pathogenic penetrating needle system. VipA and VipB (TssB and TssC) proteins were shown to form a cog-wheel like tubular structure in V. cholerae that was noticed to resemble T4 phage gp18 polysheath. Two beta-strands of VipA and four beta-strands of VipB intertwine forming the middle layer of the sheath. The sheath assembles around an inner Hcp tube and is attached to a structure called a baseplate that spans the bacterial membranes. Importantly, VipA/VipB sheath was shown to form a long contractile organelle in V. cholerae and in E. coli, suggesting that sheath contraction powers the secretion. |
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