Extended Data Fig. 5: Structure and sequence comparison of the conserved cellulose-synthase-like folds between FKS1 and BcsA.

a, The conserved fold of FKS1 (residues 615–1510) was superposed with that of BcsA (PDB ID: 4P00; residues 63–584), with an RMSD value of 4.3 Å over 308 aligned residues. BcsA is colored in grey. FKS1 core is colored in orange while FKS1-exclusive elements in its GT ___domain are in color-coded display as labeled in (a) and (b). Corresponding TM helices are denoted as labels while TM9 and TM10 are exclusive for FKS1. b, Close-up view of the superimposed GT domains in (a). The central β-sheet featured in GT ___domain gains extension in FKS1. The extended stands β6 and β7 in FKS1 and the elongated loop Lβ8-β9 contribute to a substantial portion of the interacting interface with AC ___domain in FKS1 (Fig. 1j). Moreover, two FKS1-specific sub-regions inserts to two sides of β3, the first strand of central β-sheet. The sub-region preceding β3 (residues 719–840) contains six helices and a pair of antiparallel β-strands (β1, β2); the sub-region ensuing β3 (residues 848–998) is α-helical, composed of 9 helices. These two sub-regions interact to pack the central β-sheet from one side. c, Back view of the superimposed transmembrane domains. d, Close-up view of superimposed membrane-cytosol interfaces. Interface helix IF1 is preserved in FKS1, which shows dramatic rearrangement relative to that of BcsA. Interface helix IF2 connecting a beta-sheet and transmembrane ___domain is preserved in FKS1 but disordered in the structure, which is also indicated in (c). Interface helix IF3 is gone in FKS1 and it is replaced by transmembrane helices TM9 and TM10 in FKS1. e, Structure-based sequence alignment of the conserved cellulose-synthase-like folds between FKS1 and BcsA. The alignment was first generated using PROMALS3D and then illustrated using ESPript3 server. Residues and motifs with important functions are labeled. Shown above and below the alignment are secondary structural elements derived FKS1 structure (blue symbol) and BcsA structure (PDB ID: 4P00) (orange symbol), respectively. The symbols are TM helices (filled bar), helices (empty bar) and β strands (arrow).