PDBsum entry 3a5r

Transferase

PDB id: 3a5r

Contents

Protein chains

376 a.a. *

Ligands

HC4 ×2

Waters ×554

* Residue conservation analysis

PDB id:

3a5r

Name:

Transferase

Title:

Benzalacetone synthase from rheum palmatum complexed with 4-coumaroyl- 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.

Resolution:

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

Date:

10-Aug-09 Release date: 26-Jan-10

Protein chains

Q94FV7  (BAS_RHEPA) -  Polyketide synthase BAS from Rheum palmatum

Seq: 384 a.a.

Struc: 376 a.a.

Enzyme reactions

• Enzyme class: E.C.2.3.1.212 - benzalacetone synthase.
• Reaction: 4-coumaroyl-CoA + malonyl-CoA + H2O + H⁺ = 4-hydroxybenzalacetone + 2 CO2 + 2 CoA

Molecule diagrams generated from .mol files obtained from the KEGG ftp site

reference

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.

ABSTRACT

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.