9O4G

Cryo-EM structure of the CHSY3-CHPF1 chondroitin synthase heterodimer

Summary for 9O4G

• Entry DOI: 10.2210/pdb9o4g/pdb
• EMDB information: 70100
• Descriptor: Chondroitin sulfate synthase 3, Chondroitin sulfate synthase 2, MANGANESE (II) ION, ... (4 entities in total)
• Functional Keywords: chondroitin sulfate, chondroitin sulfate synthase, sugar binding protein, transferase
• Biological source: Homo sapiens (human); More
• Total number of polymer chains: 2
• Total formula weight: 179598.08

Authors

Tehrani, D.,Cortiella, N.,Perez, C.,Moremen, K. (deposition date: 2025-04-08, release date: 2026-03-04, Last modification date: 2026-07-15)

Primary citation

Tehrani, D.,Cortiella-Valls, N.,Huang, C.,Chapla, D.,Zheng, Z.,Venkat, A.,O'Boyle, B.,Kannan, N.,Perez, C.,Moremen, K.W.
Structural basis of chondroitin sulfate backbone polymer synthesis.
Nat Commun, 2026

PubMed Abstract: Chondroitin sulfate (CS) proteoglycans are extended (-GlcAβ1,3GalNAcβ1,4-) co-polymers attached to cell surface and extracellular matrix core proteins that are further modified by extensive sulfation and epimerization. Four homologous proteins contribute to CS backbone synthesis (CHPF1, CHPF2, CHSY1, and CHSY3) and prior data suggests assembly of the proteins into heterocomplexes is required for function. Here we show by sequence alignment and structural modeling that all CHSYs and CHPFs contain an N-terminal CAZy GT31-like domain and a C-terminal GT7-like domain separated by a cystatin-like linker domain. Co-expression of one CHPF and one CHSY is required to form a soluble, functional heterodimeric CS synthase and structural modeling indicates all four potential CHSY-CHPF combinations can form equivalent heterodimeric complexes. Cryo-EM studies on CHSY3-CHPF1 confirm the structure, interface, and active site features predicted by the structural models. Enzymatic analyses of catalytic mutants demonstrate that only the glycosyltransferase domains in the CHSYs are responsible for polymer synthesis: the GT31 domain transfers β1,3-GlcA while the GT7 domain transfers β1,4-GalNAc. The corresponding CHPF domains do not contribute to polymer synthesis but stabilize the corresponding CHSY functional domains. Additional mutagenesis and modeling suggest that the bridging cystatin-like domains may contribute to efficient polymer synthesis.

PubMed: 42204168
DOI: 10.1038/s41467-026-73361-0

Experimental method

ELECTRON MICROSCOPY (3.42 Å)