Mechanism and Reaction Energy Landscape for Apiose Cross-Linking by Boric Acid in Rhamnogalacturonan II

Vivek Bharadwaj, Michael Crowley, Maria Pena, Breanna Urbanowicz, Malcolm O'Neill

Research output: Contribution to journalArticlepeer-review

7 Scopus Citations

Abstract

Rhamnogalacturonan II (RG-II) - the most complex polysaccharide known in nature - exists as a borate cross-linked dimer in the plant primary cell wall. Boric acid facilitates the formation of this cross-link on the apiosyl residues of RG-II's side chain A. Here, we detail the reaction mechanism for the cross-linking process with ab initio calculations coupled with transition state theory. We determine the formation of the first ester linkage to be the rate-limiting step of the mechanism. Our findings demonstrate that the regio- and stereospecific nature of subsequent steps in the reaction itinerary presents four distinct energetically plausible reaction pathways. This has significant implications for the overall structure of the cross-linked RG-II dimer assembly. Our transition state and reaction path analyses reveal key geometric insights that corroborate previous experimental hypotheses on borate ester formation reactions.

Original languageAmerican English
Pages (from-to)10117-10125
Number of pages9
JournalJournal of Physical Chemistry B
Volume124
Issue number45
DOIs
StatePublished - 12 Nov 2020

Bibliographical note

Publisher Copyright:
© 2020 American Chemical Society.

NREL Publication Number

  • NREL/JA-2800-77249

Keywords

  • apiose
  • borate ester
  • boric acid
  • cross-linking
  • quantum mechanics
  • reaction mechanism
  • rhamnogalacturonan-II
  • transition state theory

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