Figure 1

(A) The C\(\alpha\) trace of the apo-SeviL dimer, looking along the dimer symmetry axis. Each subunit is coloured from blue (N-terminus) to red (C-terminus), with \(\beta\)-strands shown as arrows. There is no helical secondary structure in the model. Chloride ions (associated with the B subunit) are shown as green spheres. A separate view of a single subunit is shown on the right, looking along the pseudo-symmetry of the \(\beta\)-trefoil fold. The three tryptophan residues are shown as pink sticks, and reflect the internal symmetry of the protein chain. Structural figures were drawn using PYMOL²⁶, which was used to detect secondary structure automatically. (B) A sequence alignment of the three subdomains of SeviL. Crosses over the sequence indicate the residues in the \(\alpha\) subdomain that contact the sugar ligand. Colons indicate conservation of residue type, and the asterisk shows the only residue conserved in each subdomain, the tryptophan. (C) Molecular weight estimation by sedimentation velocity experiment as described in Methods/Analytical Ultracentrifugation. Wild-type SeviL shows a mass corresponding to the dimer, but the double mutant SeviL(Q12R/F126K) is almost entirely monomeric. A high rotation speed (50,000 rpm) was used to give better separation of species by mass, so the arbitrary concentration units reflect the presence of monomer and dimer.