Structural and Biochemical Insight into a Modular ..beta..-1,4-Galactan Synthase in Plants

Pradeep Kumar Prabhakar, Jose Henrique Pereira, Rahil Taujale, Wanchen Shao, Vivek Bharadwaj, Digantkumar Chapla, Jeong-Yeh Yang, Yannick Bomble, Kelley Moremen, Natarajan Kannan, Michal Hammel, Paul Adams, Henrik Scheller, Breeanna Urbanowicz

Research output: Contribution to journalArticlepeer-review

3 Scopus Citations


Rhamnogalacturonan I (RGI) is a structurally complex pectic polysaccharide with a backbone of alternating rhamnose and galacturonic acid residues substituted with arabinan and galactan side chains. Galactan synthase 1 (GalS1) transfers galactose and arabinose to either extend or cap the β-1,4-galactan side chains of RGI, respectively. Here we report the structure of GalS1 from Populus trichocarpa, showing a modular protein consisting of an N-terminal domain that represents the founding member of a new family of carbohydrate-binding module, CBM95, and a C-terminal glycosyltransferase family 92 (GT92) catalytic domain that adopts a GT-A fold. GalS1 exists as a dimer in vitro, with stem domains interacting across the chains in a ‘handshake’ orientation that is essential for maintaining stability and activity. In addition to understanding the enzymatic mechanism of GalS1, we gained insight into the donor and acceptor substrate binding sites using deep evolutionary analysis, molecular simulations and biochemical studies. Combining all the results, a mechanism for GalS1 catalysis and a new model for pectic galactan side-chain addition are proposed.

Original languageAmerican English
Pages (from-to)486-500
Number of pages15
JournalNature Plants
Issue number3
StatePublished - Mar 2023

Bibliographical note

Publisher Copyright:
© 2023, The Author(s), under exclusive licence to Springer Nature Limited.

NREL Publication Number

  • NREL/JA-2800-84906


  • docking
  • galactosyl transferase
  • molecular dynamics
  • Rhamnogalacturonan-I
  • x-ray crystallography


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