Extended Data Fig. 2: Details of the TcA–TcB interface.

a, Interactions at the TcA–TcB interface. Binding of TcA to TcB–TcC is stabilized by interactions between the pseudo-six-fold symmetrical β-propeller of TcB and the five-fold symmetrical TcB-binding domain of TcA. The gatekeeper domain, shown in blue, undergoes the largest conformational changes during gate opening. In the open state, residues R485 (i) and K534 (iv) of blades 3 and 4, respectively, are positioned within negatively charged grooves of the TcB-binding domain of TcA. In addition, two copies of residue L2422 of two adjacent TcA subunits are positioned within a prominent hydrophobic groove of blade 3 (ii) and 4 (iii), respectively. Interacting residues of TcB are shown as sticks. Surfaces of TcA involved in the interfaces are coloured from high (orange) to low (white) hydrophobicity (ii, iii, vi) or according the Coulomb potential (ranging from −10 kcal mol⁻¹ (red) to 10 kcal mol⁻¹ (blue) at pH 7.5 (i, iv, v)). Similar to the interfaces between blade 3 and 4 and TcA, blade 5 forms strong hydrophobic interactions with residue L2422 of TcA (vi) and electrostatic interactions with negatively charged patches of the opposing TcA domain (v). In contrast to the other blades, no prominent electrostatic or hydrophobic interactions can be observed with high certainty at this interface. Several candidates for amino acid residues were identified as putative hydrogen bond donors or acceptors (vii, viii). Colours correspond to those in Fig. 1. b, Conservation of residues at the TcA–TcB interface. Positions of residues of the β-propeller domain of TcB interacting with TcA are shown as in a. The model of the β-propeller domain is coloured according to sequence conservation, with cyan representing non-conserved residues and magenta representing highly conserved residues. The TcB-binding domain of TcA is shown in light green. c, Sequence alignment of TcB sequences. Asterisks indicate the positions of the residues highlighted in b. The sequence of P. luminescens TcdB2 is outlined. The alignment is coloured according to b.