Crystal Structures of Ethanolamine Ammonia-lyase Complexed with Coenzyme B12 Analogs and Substrates

Abstract

N-terminal truncation of the

Converging on a mechanism for choline degradation

“…Partial protonation of the migrating amine group and partial deprotonation of the hydroxyl group at C1 by active site amino acids likely play critical, synergistic roles in lowering the energy of the transition state leading to migration (13,15). Consistent with this hypothesis, a recent Xray crystal structure of EAL from E. coli revealed a constellation of conserved acid/ base and polar amino acid residues that seemed poised to guide the amine group along a 1,2-migration trajectory (16). After amine migration, the reactive carbinolamine radical (10, Scheme 2) abstracts a hydrogen atom from 5′-dAdo to form carbinolamine (12, Scheme 2) and regenerate the resting state of the AdoCbl coenzyme.…”

Microbial conversion of choline to trimethylamine requires a glycyl radical enzyme

“…In bacteria, the enzymes required for ethanolamine utilization are encoded by the eut gene cluster (21). An initial C-N bond cleavage is performed by ethanolamine ammonia-lyase (EutBC), a vitamin B 12 -dependent enzyme that generates ammonia and acetaldehyde (22). The acetaldehyde produced in this initial step is further processed by alcohol dehydrogenase EutG and aldehyde oxidoreductase EutE to give ethanol and acetyl coenzyme A (acetyl CoA) (21).…”

“…A critical distinction between choline and metabolites processed by B 12 -dependent pathways, such as ethanolamine, is the presence of a trimethylammonium substituent. Choline lacks N-H bonds and therefore cannot make all of the hydrogen bonding contacts within an enzymeactive site that are considered important for catalysis of B 12 -dependent eliminations (22,33). Although this crucial structural difference called into question whether analogies in pathway logic between choline and ethanolamine utilization would extend to the C-N bond cleaving event, it was evident that powerful enzymatic chemistry would be needed to perform this transformation.…”

Is There a Dynamic Protein Contribution to the Substrate Trigger in Coenzyme B12‐Dependent Ethanolamine Ammonia Lyase?

“…It is also considered to play an intimate role in the "substrate trigger", contributing to steric strain, ribosyl rotation and stabilization of the RP state. [34] This all raises the intriguing possibility of a dynamic contribution to the substrate trigger in EAL. Our data suggest it may be subtle, and therefore likely to happen in cohort with other factors.…”