Publications

• Probing the active site of MIO-dependent aminomutases, key catalysts in the biosynthesis of beta-amino acids incorporated in secondary metabolites.

  Cooke H.A., Bruner S.D.

  The tyrosine aminomutase SgTAM produces (S)-ss-tyrosine from L-tyrosine in the biosynthesis of the enediyne antitumor antibiotic C-1027. This conversion is promoted by the methylideneimidazole-5-one (MIO) prosthetic group. MIO was first identified in the homologous family of ammonia lyases, which ... >> More

  The tyrosine aminomutase SgTAM produces (S)-ss-tyrosine from L-tyrosine in the biosynthesis of the enediyne antitumor antibiotic C-1027. This conversion is promoted by the methylideneimidazole-5-one (MIO) prosthetic group. MIO was first identified in the homologous family of ammonia lyases, which deaminate aromatic amino acids to form alpha,ss-unsaturated carboxylates. Studies of substrate specificity have been described for lyases but there have been limited reports in altering the substrate specificity of aminomutases. Furthermore, it remains unclear as to what structural properties are responsible for catalyzing the presumed readdition of the amino group into the alpha,ss-unsaturated intermediates to form ss-amino acids. Attempts to elucidate specificity and mechanistic determinants of SgTAM have also proved to be difficult as it is recalcitrant to perturbations to the active site via mutagenesis. An X-ray cocrystal structure of the SgTAM mutant of the catalytic base with L-tyrosine verified important substrate binding residues as well as the enzymatic base. Further mutagenesis revealed that removal of these crucial interactions renders the enzyme inactive. Proposed structural determinants for mutase activity probed via mutagenesis, time-point assays and X-ray crystallography revealed a complicated role for these residues in maintaining key quaternary structure properties that aid in catalysis. << Less

  Biopolymers 93:802-810(2010) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• A bacterial tyrosine aminomutase proceeds through retention or inversion of stereochemistry to catalyze its isomerization reaction.

  Wanninayake U., Walker K.D.

  β-Amino acids are biologically active compounds of interest in medicinal chemistry. A class I lyase-like family of aminomutases isomerizes (S)-α-arylalanines to the corresponding β-amino acids by exchange of the NH2/H pair. This family uses a 3,5-dihydro-5-methylidene-4H-imidazol-4-one (MIO) group ... >> More

  β-Amino acids are biologically active compounds of interest in medicinal chemistry. A class I lyase-like family of aminomutases isomerizes (S)-α-arylalanines to the corresponding β-amino acids by exchange of the NH2/H pair. This family uses a 3,5-dihydro-5-methylidene-4H-imidazol-4-one (MIO) group within the active site to initiate the reaction. The absolute stereochemistry of the product is known for an MIO-dependent tyrosine aminomutase from Chondromyces crocatus (CcTAM) that isomerizes (S)-α-tyrosine to (R)-β-tyrosine. To evaluate the cryptic stereochemistry of the CcTAM mechanism, (2S,3S)-[2,3-(2)H2]- and (2S,3R)-[3-(2)H]-α-tyrosine were stereoselectively synthesized from unlabeled (or [(2)H]-labeled) (4'-hydroxyphenyl)acrylic acids by reduction with D2 (or H2) gas and a chiral Rh-Prophos catalyst. GC/EIMS analysis of the [(2)H]-β-tyrosine biosynthesized by CcTAM revealed that the α-amino group was transferred to Cβ of the phenylpropanoid skeleton with retention of configuration. These labeled substrates also showed that the pro-(3S) proton exchanges with protons from the bulk media during its migration to Cα during catalysis. (1)H- and (2)H NMR analyses of the [(2)H]-β-tyrosine derived from (2S)-[3,3-(2)H2]-α-tyrosine by CcTAM catalysis showed that the migratory proton attached to Cα of the product also with retention of configuration. CcTAM is stereoselective for (R)-β-tyrosine (85%) yet also forms the (S)-β-tyrosine enantiomer (15%) through inversion of configuration at both migration termini, as described herein. The proportion of the (S)-β-isomer made by CcTAM during steady state interestingly increased with solvent pH, and this effect on the proposed reaction mechanism is also discussed. << Less

  J Am Chem Soc 135:11193-11204(2013) [PubMed] [EuropePMC]

• Discovery of additional members of the tyrosine aminomutase enzyme family and the mutational analysis of CmdF.

  Krug D., Muller R.

  The tyrosine aminomutase (TAM) CmdF converts L-Tyr preferentially to (R)-beta-Tyr--a biosynthetic building block subsequently incorporated into the highly cytotoxic chondramides by the myxobacterium Chondromyces crocatus. Together with the similar enzymes SgcC4 from Streptomyces globisporus and Md ... >> More

  The tyrosine aminomutase (TAM) CmdF converts L-Tyr preferentially to (R)-beta-Tyr--a biosynthetic building block subsequently incorporated into the highly cytotoxic chondramides by the myxobacterium Chondromyces crocatus. Together with the similar enzymes SgcC4 from Streptomyces globisporus and MdpC4 from Actinomadura madurae, which preferentially produce (S)-beta-Tyr, CmdF belongs to a novel 2,3-aminomutase enzyme family closely related to the aromatic amino acid ammonia lyase. Although considerable insight into the underlying catalytic mechanism has been provided recently by structural and mechanistic studies, the key determinants of product specificity and stereochemical preference of TAM enzymes remain to be elucidated in detail. We report herein the discovery and heterologous expression of additional TAMs from prokaryotic sources. These studies reveal a high degree of evolutionary diversification within this expanding enzyme family. Attempts to genetically engineer CmdF to exhibit ammonia lyase-type activity by the exchange of conserved sequence motifs were largely unsuccessful. However, the variation of a semiconserved glutamic acid residue was found to impact stereoselectivity. Replacement of this residue by lysine significantly increased the enantiomeric excess of (R)-beta-Tyr from 69 to 97 % ee, while substitution with methionine promoted racemization. These results suggest that it should be possible to elucidate a mechanism for control of stereoselectivity in the TAM family by the application of directed evolution to CmdF. Furthermore, our findings indicate the potential to fine-tune the catalytic properties of TAMs for their use as biocatalysts or in engineered biosynthetic pathways. << Less

  ChemBioChem 10:741-750(2009) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.