PDBsum entry 3a5r

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Transferase PDB id
Protein chains
376 a.a. *
HC4 ×2
Waters ×554
* Residue conservation analysis
PDB id:
Name: Transferase
Title: Benzalacetone synthase from rheum palmatum complexed with 4- primed monoketide intermediate
Structure: Benzalacetone synthase. Chain: a, b. Engineered: yes
Source: Rheum palmatum. Organism_taxid: 137221. Gene: bas. Expressed in: escherichia coli. Expression_system_taxid: 562.
1.60Å     R-factor:   0.195     R-free:   0.215
Authors: H.Morita,R.Kato,I.Abe,S.Sugio,T.Kohno
Key ref: H.Morita et al. (2010). A structure-based mechanism for benzalacetone synthase from Rheum palmatum. Proc Natl Acad Sci U S A, 107, 669-673. PubMed id: 20080733
10-Aug-09     Release date:   26-Jan-10    
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Protein chains
Pfam   ArchSchema ?
Q94FV7  (Q94FV7_9CARY) -  Polyketide synthase BAS
384 a.a.
376 a.a.
Key:    PfamA domain  Secondary structure  CATH domain

 Enzyme reactions 
   Enzyme class: E.C.  - Benzalacetone synthase.
[IntEnz]   [ExPASy]   [KEGG]   [BRENDA]
      Reaction: 4-coumaroyl-CoA + malonyl-CoA + H2O = 2 CoA + 4-hydroxybenzalacetone + 2 CO2
+ malonyl-CoA
+ H(2)O
= 2 × CoA
+ 4-hydroxybenzalacetone
+ 2 × CO(2)
Molecule diagrams generated from .mol files obtained from the KEGG ftp site
 Gene Ontology (GO) functional annotation 
  GO annot!
  Biological process     metabolic process   4 terms 
  Biochemical function     catalytic activity     5 terms  


Proc Natl Acad Sci U S A 107:669-673 (2010)
PubMed id: 20080733  
A structure-based mechanism for benzalacetone synthase from Rheum palmatum.
H.Morita, Y.Shimokawa, M.Tanio, R.Kato, H.Noguchi, S.Sugio, T.Kohno, I.Abe.
Benzalacetone synthase (BAS), a plant-specific type III polyketide synthase (PKS), catalyzes a one-step decarboxylative condensation of malonyl-CoA and 4-coumaroyl-CoA to produce the diketide benzalacetone. We solved the crystal structures of both the wild-type and chalcone-producing I207L/L208F mutant of Rheum palmatum BAS at 1.8 A resolution. In addition, we solved the crystal structure of the wild-type enzyme, in which a monoketide coumarate intermediate is covalently bound to the catalytic cysteine residue, at 1.6 A resolution. This is the first direct evidence that type III PKS utilizes the cysteine as the nucleophile and as the attachment site for the polyketide intermediate. The crystal structures revealed that BAS utilizes an alternative, novel active-site pocket for locking the aromatic moiety of the coumarate, instead of the chalcone synthase's coumaroyl-binding pocket, which is lost in the active-site of the wild-type enzyme and restored in the I207L/L208F mutant. Furthermore, the crystal structures indicated the presence of a putative nucleophilic water molecule which forms hydrogen bond networks with the Cys-His-Asn catalytic triad. This suggested that BAS employs novel catalytic machinery for the thioester bond cleavage of the enzyme-bound diketide intermediate and the final decarboxylation reaction to produce benzalacetone. These findings provided a structural basis for the functional diversity of the type III PKS enzymes.