A single point mutation in a TssB/VipA homolog disrupts sheath formation in the type VI secretion system of Proteus mirabilis
Fig 2
The L32R mutation on a model of the P. mirabilis BB2000 T6S sheath.
(A) Cartoon representation of the P. mirabilis BB2000 TssB monomer (cyan) modeled after the V. cholerae TssB homolog [25]. The wild-type TssB variant has a leucine (yellow) at position 32. The mutant variant TssBL32R has an arginine (light blue) at position 32. (B, C) Cartoon representation of a portion of the wild-type P. mirabilis BB2000 T6S sheath containing TssBwt and the P. mirabilis BB2000 TssC homolog (BB2000_0820) at two magnifications. It was modeled after the V. cholerae contracted sheath [25]. In this model, one complete TssB-TssC protomer is highlighted, with TssB shown in cyan and TssC shown in pink. Two additional TssC monomers are highlighted in magenta and light pink. The wild-type TssB variant has a leucine (yellow) at position 32, which we have mapped to a predicted unstructured region between two beta sheets. Both beta sheets are thought to be involved in making contacts to TssC monomers [25, 26]. (D, E) Magnified view of residue 32 and the neighboring residues (glycine in orange, valine in green, and arginine in dark blue). (D) Wild-type leucine in yellow. (E) Mutant arginine in light blue. Swiss-Model [45–48] was used for all modeling, and the atomic model 3j9g (from http://www.rcsb.org [25, 49, 50]) was used as a template. Resulting.pdb files were modified in PyMOL v1.8.4.1 [51].