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Crystal structure of the plant PPC decarboxylase AtHAL3a complexed with an ene-thiol reaction intermediate

Steinbacher, Stefan, Hernández-Acosta, Pilar, Bieseler, Bastian, Blaesse, Michael, Huber, Robert, Culiáñez-Macià, Francisco Antonio and Kupke, Thomas 2003. Crystal structure of the plant PPC decarboxylase AtHAL3a complexed with an ene-thiol reaction intermediate. Journal of Molecular Biology 327 (1) , pp. 193-202. 10.1016/S0022-2836(03)00092-5

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The Arabidopsis thaliana protein AtHAL3a decarboxylates 4′-phosphopantothenoylcysteine to 4′-phosphopantetheine, a step in coenzyme A biosynthesis. Surprisingly, this decarboxylation reaction is carried out as an FMN-dependent redox reaction. In the first half-reaction, the side-chain of the cysteine residue of 4′-phosphopantothenoylcysteine is oxidised and the thioaldehyde intermediate decarboxylates spontaneously to the 4′-phosphopantothenoyl-aminoethenethiol intermediate. In the second half-reaction this compound is reduced to 4′-phosphopantetheine and the FMNH2 cofactor is re-oxidised. The active site mutant C175S is unable to perform this reductive half-reaction. Here, we present the crystal structure of the AtHAL3a mutant C175S in complex with the reaction intermediate pantothenoyl-aminoethenethiol and FMNH2. The geometry of binding suggests that reduction of the CαCβ double bond of the intermediate can be performed by direct hydride-transfer from N5 of FMNH2 to Cβ of the aminoethenethiol-moiety supported by a protonation of Cα by Cys175. The binding mode of the substrate is very similar to that previously observed for a pentapeptide to the homologous enzyme EpiD that introduces the aminoethenethiol-moiety as final reaction product at the C terminus of peptidyl-cysteine residues. This finding further supports our view that these homologous enzymes form a protein family of homo-oligomeric flavin-containing cysteine decarboxylases, which we have termed HFCD family.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Biosciences
Publisher: Elsevier
ISSN: 0022-2836
Last Modified: 24 Jun 2017 11:00

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