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A model of dirigent proteins derived from structural and functional similarities with allene oxide cyclase and lipocalins
Author(s) -
Pickel Benjamin,
Pfannstiel Jens,
Steudle Alexander,
Lehmann Axel,
Gerken Uwe,
Pleiss Jürgen,
Schaller Andreas
Publication year - 2012
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2012.08580.x
Subject(s) - chemistry , stereochemistry , antiparallel (mathematics) , allene , protein structure , homology modeling , biochemistry , enzyme , physics , quantum mechanics , magnetic field , catalysis
Dirigent proteins impart stereoselectivity on the phenoxy radical‐coupling reaction, yielding optically active lignans from two molecules of coniferyl alcohol. By an unknown mechanism, they direct the coupling of two phenoxy radicals toward the formation of optically active (+)‐ or (−)‐pinoresinol. We show here that the dirigent protein AtDIR6 from Arabidopsis thaliana is a homodimeric all‐beta protein in the superfamily of calycins. Based on its homology with calycins, the structure of AtDIR6 was modeled using allene oxide cyclase as template. The structural model of AtDIR6 was supported experimentally by confirmation of a predicted disulfide bridge and by the characterization of two N‐linked glycans at the solvent‐exposed protein surface. The model shows AtDIR6 as an eight‐stranded antiparallel β‐barrel with a central hydrophobic cavity for substrate binding, suggesting that dirigent proteins evolved from hydrophobic ligand‐binding proteins. The data are fully consistent with the current view of the dirigent protein mode of action, according to which each subunit of the homodimer captures one of the substrate radicals and orients them in a way that precludes undesired reaction channels, thus favoring the formation of the optically pure coupling product. Structured digital abstract • AtDIR6 and AtDIR6 bind by cross‐linking study ( View interaction ) • AtDIR6 and AtDIR6 bind by molecular sieving ( View interaction )