4EX9

Crystal structure of the prealnumycin C-glycosynthase AlnA in complex with ribulose 5-phosphate


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 3.15 Å
  • R-Value Free: 0.248 
  • R-Value Work: 0.220 
  • R-Value Observed: 0.221 

Starting Model: experimental
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This is version 1.4 of the entry. See complete history


Literature

Structural basis for C-ribosylation in the alnumycin A biosynthetic pathway.

Oja, T.Niiranen, L.Sandalova, T.Klika, K.D.Niemi, J.Mantsala, P.Schneider, G.Metsa-Ketela, M.

(2013) Proc Natl Acad Sci U S A 110: 1291-1296

  • DOI: https://doi.org/10.1073/pnas.1207407110
  • Primary Citation of Related Structures:  
    4EX6, 4EX7, 4EX8, 4EX9

  • PubMed Abstract: 

    Alnumycin A is an exceptional aromatic polyketide that contains a carbohydrate-like 4'-hydroxy-5'-hydroxymethyl-2',7'-dioxane moiety attached to the aglycone via a carbon-carbon bond. Recently, we have identified the D-ribose-5-phosphate origin of the dioxane unit and demonstrated that AlnA and AlnB are responsible for the overall C-ribosylation reaction. Here, we provide direct evidence that AlnA is a natural C-glycosynthase, which catalyzes the attachment of D-ribose-5-phosphate to prealnumycin by formation of the C(8)-C(1') bond as demonstrated by the structure of the intermediate alnumycin P. This compound is subsequently dephosphorylated by AlnB, an enzyme of the haloacid dehalogenase superfamily. Structure determination of the native trimeric AlnA to 2.1-Å resolution revealed a highly globular fold encompassing an α/β/α sandwich. The crystal structure of the complex with D-ribose-5-phosphate indicated that the phosphosugar is bound in the open-chain configuration. Identification of residues E29, K86, and K159 near the C-1 carbonyl of the ligand led us to propose that the carbon-carbon bond formation proceeds through a Michael-type addition. Determination of the crystal structure of the monomeric AlnB in the open conformation to 1.25-Å resolution showed that the protein consists of core and cap domains. Modeling of alnumycin P inside the cap domain positioned the phosphate group next to a Mg(2+) ion present at the junction of the domains. Mutagenesis data were consistent with the canonical reaction mechanism for this enzyme family revealing the importance of residues D15 and D17 for catalysis. The characterization of the prealnumycin C-ribosylation illustrates an alternative means for attachment of carbohydrates to natural products.


  • Organizational Affiliation

    Department of Biochemistry and Food Chemistry, University of Turku, FIN-20014 Turku, Finland.


Macromolecules
Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
AlnA316Streptomyces sp. CM020Mutation(s): 0 
Gene Names: alnA
UniProt
Find proteins for B6SEG5 (Streptomyces sp. CM020)
Explore B6SEG5 
Go to UniProtKB:  B6SEG5
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupB6SEG5
Sequence Annotations
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  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 3.15 Å
  • R-Value Free: 0.248 
  • R-Value Work: 0.220 
  • R-Value Observed: 0.221 
  • Space Group: I 41 3 2
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 168.79α = 90
b = 168.79β = 90
c = 168.79γ = 90
Software Package:
Software NamePurpose
DNAdata collection
MOLREPphasing
REFMACrefinement
MOSFLMdata reduction
SCALAdata scaling

Structure Validation

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Ligand Structure Quality Assessment 


Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2013-01-16
    Type: Initial release
  • Version 1.1: 2013-02-13
    Changes: Database references
  • Version 1.2: 2018-01-24
    Changes: Structure summary
  • Version 1.3: 2024-02-28
    Changes: Data collection, Database references, Derived calculations
  • Version 1.4: 2024-04-03
    Changes: Refinement description