Fig. 3: Active site and self-priming of Chs1.
From: Structure, catalysis, chitin transport, and selective inhibition of chitin synthase
a Close-up view of the active site of Chs1 (green) in complex with UDP-GlcNAc donor, GlcNAc acceptor (purple), and Mg2+ (lime). Key residues are shown in stick representation. b Structural alignment of Chs1 in apo, UDP-GlcNAc bound, UDP-GlcNAc+GlcNAc bound, and UDP bound states. The red arrow marks the switch loop of Chs1 moving from the apo position to the flipped position. c Growth complementation of wild-type w303 cells (w303) and chs1Δ cells with empty plasmid (chs1Δ) or plasmid carrying either wild-type Chs1 (WT) or mutants. Representative cell images are shown in Supplementary Fig. 13. Cell string refers to a string of unseparated cells with number ≥3. For each of these strains, >2000 cells were counted and calculated using w303 and chs1Δ as negative and positive controls. The phenotype of the cell string is an indicator of how much Chs1’s function is disrupted in vivo. d Structural comparison between UDP-GlcNAc donor-bound Chs1 (purple) and primed UDP+GlcNAc-bound Chs1 (cyan) by aligning their TMs. The orange arrow marks the shift of the GT domain and nucleotide toward the membrane from the donor-bound state to the primed state. The active site is highlighted by a blue rectangle. The sugar donor is highlighted by a yellow rectangle. e Close-up view of the active site of primed Chs1 (cyan) in complex with UDP, GlcNAc, and two Mg2+ ions (lime). This is enlargement of the blue rectangle in (d) viewed from left. Substrates and key residues are shown in stick representation. f Enlargement of the yellow rectangle in (d) viewed from back. The UDP (cyan) and Mg2+ (lime) of primed Chs1, and UDP-GlcNAc (purple) and Mg2+ (purple) of the donor-bound Chs1 are shown. α-, β-phosphates are labeled, highlighting a 180° rotation of the β-phosphate from UDP-GlcNAc to UDP.
