Thursday, August 2, 2007 - 2:00 PM
S184
Enantiocomplementary enzymes: Molecular basis for reversed enantiopreference and prospects for mirror-image biotransformations
Romas Kazlauskas1, Paul Mugford1, Yun Jiang1, Kurt Faber2, and Ulrike Wagner3. (1) Dept. of Biochemistry, Mol. Biol. & Biophysics, University of Minnesota, 1479 Gortner Ave., St. Paul, MN 55108, (2) Dept. of Chemistry, University of Graz, Heinrichstrasse 28, Graz, A8010, Austria, (3) Dept. of Structural Biology, University of Graz, Graz, Austria
Enantiocomplementary enzymes catalyze the same reaction, but yield opposite enantiomers. X-ray crystal structures of enantiocomplementary enzymes reveal that this reversal may involve either changing the substrate orientation or moving the catalytic residues. We classified enantiocomplemtary enzymes into five categories based on how they reverse their enantiopreference:
(i) Enantiomeric enzymes in a strict sense have been made by chemical synthesis from D-amino acids; these are in-principle demonstrations only.
(ii) Racemases possess a 'quasi-symmetic' arrangement of chemical operators within the ac-tive site and transform both enantiomers at comparable rates; these are non-enantioselective enzymes and not enantiocomplementary in the strict sense.
(iii) Enantiocomplementary enzyme may contain a complete 'mirror-image' orientation of the catalytic machinery (e.g. lipases and subtilisins); this normally requires a different protein fold.
(iv) Enantiocomplementary enzymes with an identical arrangement of the main chemical op-erators, but an altered substrate binding pocket that favors the enantiomeric substrate (e.g., dehydrogenases or amino acid oxidases)
(v) Altered orientation of some key of the catalytic residue(s) leads to the formation of enan-tiomeric products (e.g, vanillyl alcohol oxidase).
This survey demonstrates suggests several new approaches to mirror-image biotransformations. First, enantiocomplementary enzymes are more common than generally thought, so screening or genome mining may yield an enantiocomplementary enzyme. Second, pairwise mutagenesis to re-verse the location of a substrate-binding or catalytic residue may be a good strategy to reverse the enantioperference of an existing enzyme.
(i) Enantiomeric enzymes in a strict sense have been made by chemical synthesis from D-amino acids; these are in-principle demonstrations only.
(ii) Racemases possess a 'quasi-symmetic' arrangement of chemical operators within the ac-tive site and transform both enantiomers at comparable rates; these are non-enantioselective enzymes and not enantiocomplementary in the strict sense.
(iii) Enantiocomplementary enzyme may contain a complete 'mirror-image' orientation of the catalytic machinery (e.g. lipases and subtilisins); this normally requires a different protein fold.
(iv) Enantiocomplementary enzymes with an identical arrangement of the main chemical op-erators, but an altered substrate binding pocket that favors the enantiomeric substrate (e.g., dehydrogenases or amino acid oxidases)
(v) Altered orientation of some key of the catalytic residue(s) leads to the formation of enan-tiomeric products (e.g, vanillyl alcohol oxidase).
This survey demonstrates suggests several new approaches to mirror-image biotransformations. First, enantiocomplementary enzymes are more common than generally thought, so screening or genome mining may yield an enantiocomplementary enzyme. Second, pairwise mutagenesis to re-verse the location of a substrate-binding or catalytic residue may be a good strategy to reverse the enantioperference of an existing enzyme.