Fig. 7
From: Structural insights into the function of type VI secretion system TssA subunits
Schematic representation of TssA ring dimensions and domain flexibility. a Arrangement of the Ah TssA2A Nt2 domains around the CTD oligomer as observed in the asymmetric unit. The Nt2 domains do not follow strict five-fold symmetry. The decameric CTD ring is shown in dark grey perpendicular to the five-fold (left) and two-fold (right) axes with each peripheral Nt2 dimer shown in a different colour. The diagram between the two structures shows the relationship between dimer-forming Nt2 domains (represented by coloured squares) and their corresponding C-terminal domains in the TssA2A Nt2-CTD decamer. b Displacement of the Ah TssA2A Nt2 dimers perpendicular to the five-fold axis of the CTD oligomer. The CTD ring is shown in light grey with one WEP-mediated CTD dimer indicated in cyan to which is tethered an Nt2 dimer. The Nt2 dimer (light green) is shown at its maximum displacement of ~60° either side of the plane of the CTD ring (orange line). Other observed positions of Nt2 are indicated by translucent shading. c Top and side view representations showing the domain architecture of TssA subunits from clades 1B, 2A and 2B modelled on the baseplate-distal end of the T6SS tube/sheath assembly during polymerisation. The V. cholerae TssBC extended sheath (green) surrounding a Hcp hexamer (yellow) (PDB: 5MXN) is shown on the left. Onto this, is modelled the TssA1B CTD oligomer (orange) with 16-fold symmetry, showing one stacked CTD dimer attached to a pair of Nt1 domains via flexible linkers, the TssA2A CTD oligomer (blue) with five-fold symmetry, showing a WEP-mediated CTD dimer connected to the two monomers of an Nt2 dimer via flexible linkers, each of which are in turn connected to an Nt1 domain, and the TssA2B CTD oligomer (red) displaying six-fold symmetry, showing a CTD dimer connected to the two monomers of an Nt2 dimer via flexible linkers, each of which are in turn connected to an Nt1 domain. Labels are: C, CTD dimers (top view); N1, Nt1; N2, Nt2; CTD, CTD oligomer (side view). Scale bar corresponds to 65 Å
