title: How coenzyme B12-dependent ethanolamine ammonia-lyase deals with both enantiomers of 2-amino-1-propanol as substrates: structure-based rationalization.
abstract: Coenzyme B(12)-dependent ethanolamine ammonia-lyase acts on both enantiomers of the substrate 2-amino-1-propanol [Diziol, P., et al. (1980) Eur. J. Biochem. 106, 211-224]. To rationalize this apparent lack of stereospecificity and the enantiomer-specific stereochemical courses of the deamination, we analyzed the X-ray structures of enantiomer-bound forms of the enzyme-cyanocobalamin complex. The lower affinity for the (R)-enantiomer may be due to the conformational change of the Valα326 side chain of the enzyme. In a manner consistent with the reported experimental results, we can predict that the pro-S hydrogen atom on C1 is abstracted by the adenosyl radical from both enantiomeric substrates, because it is the nearest one in both enantiomer-bound forms. We also predicted that the NH(2) group migrates from C2 to C1 by a suprafacial shift, with inversion of configuration at C1 for both enantiomeric substrates, although the absolute configuration of the 1-amino-1-propanol intermediate is not yet known. Reported labeling experiments demonstrate that (R)-2-amino-1-propanol is deaminated by the enzyme with inversion of configuration at C2, whereas the (S)-enantiomer is deaminated with retention. By taking these results into consideration, we can predict the rotameric radical intermediate from the (S)-enantiomer undergoes flipping to the rotamer from the (R)-enantiomer before the hydrogen back-abstraction. This suggests the preference of the enzyme active site for the rotamer from the (R)-enantiomer in equilibration. This preference might be explained in terms of the steric repulsion of the (S)-enantiomer-derived product radical at C3 with the Pheα329 and Leuα402 residues.
authors.affiliation: Department of Life Science, Graduate School of Life Science, University of Hyogo, 3-2-1 Koto, Kamigori-cho, Ako-gun, Hyogo, Japan. shibach@sci.u-hyogo.ac.jp
authors.forename: Naoki
authors.initials: N
authors.lastname: Shibata
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Higuchi
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Toraya
mesh_terms: D020134:Catalytic Domain; D003038:Cobamides / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism; D004981:Ethanolamine Ammonia-Lyase / Q000737:chemistry* / Q000378:metabolism; D011237:Predictive Value of Tests; D011412:Propanolamines / Q000737:chemistry*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D003038:Cobamides; D029968:Escherichia coli Proteins; D011412:Propanolamines; C034448:2-aminopropanol; D004981:Ethanolamine Ammonia-Lyase; C000913:cobamamide