O-acetylserine sulfhydrylase from Citrullus vulgaris in the internal aldimine state, with citrate bound

Experimental Data Snapshot

  • Resolution: 1.55 Å
  • R-Value Free: 0.191 
  • R-Value Work: 0.177 
  • R-Value Observed: 0.178 

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Investigation of beta-Substitution Activity of O-Acetylserine Sulfhydrolase from Citrullus vulgaris.

Smith, J.L.Harrison, I.M.Bingman, C.A.Buller, A.R.

(2022) Chembiochem 23: e202200157-e202200157

  • DOI: https://doi.org/10.1002/cbic.202200157
  • Primary Citation of Related Structures:  

  • PubMed Abstract: 

    Pyridoxal-5'-phosphate (PLP)-dependent enzymes have garnered interest for their ability to synthesize non-standard amino acids (nsAAs). One such class of enzymes, O-acetylserine sulfhydrylases (OASSs), catalyzes the final step in the biosynthesis of l-cysteine. Here, we examine the β-substitution capability of the OASS from Citrullus vulgaris (CvOASS), a putative l-mimosine synthase. While the previously reported mimosine synthase activity was not reproducible in our hands, we successfully identified non-native reactivity with a variety of O-nucleophiles. Optimization of reaction conditions for carboxylate and phenolate substrates led to distinct conditions that were leveraged for the preparative-scale synthesis of nsAAs. We further show this enzyme is capable of C-C bond formation through a β-alkylation reaction with an activated nitroalkane. To facilitate understanding of this enzyme, we determined the crystal structure of the enzyme bound to PLP as the internal aldimine at 1.55 Å, revealing key features of the active site and providing information that may guide subsequent development of CvOASS as a practical biocatalyst.

  • Organizational Affiliation

    Department of Biochemistry, University of Wisconsin-Madison, 433 Babcock Drive, Madison, Wisconsin, 53706, USA.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Cysteine synthase333Citrullus lanatus subsp. vulgarisMutation(s): 0 
EC: (PDB Primary Data), (PDB Primary Data), (PDB Primary Data), (PDB Primary Data)
Find proteins for Q43317 (Citrullus lanatus)
Explore Q43317 
Go to UniProtKB:  Q43317
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupQ43317
Sequence Annotations
  • Reference Sequence
Small Molecules
Modified Residues  1 Unique
IDChains TypeFormula2D DiagramParent
Query on LLP
Experimental Data & Validation

Experimental Data

  • Resolution: 1.55 Å
  • R-Value Free: 0.191 
  • R-Value Work: 0.177 
  • R-Value Observed: 0.178 
  • Space Group: C 1 2 1
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 97.207α = 90
b = 63.591β = 91.45
c = 66.918γ = 90
Software Package:
Software NamePurpose
PDB_EXTRACTdata extraction
XDSdata reduction
XSCALEdata scaling

Structure Validation

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Ligand Structure Quality Assessment 

Entry History & Funding Information

Deposition Data

Funding OrganizationLocationGrant Number
National Institutes of Health/National Institute of General Medical Sciences (NIH/NIGMS)United States1DP2GM137417-01

Revision History  (Full details and data files)

  • Version 1.0: 2022-07-06
    Type: Initial release
  • Version 1.1: 2023-02-08
    Changes: Database references