Synthesis of short-chain diols and unsaturated alcohols from secondary alcohol substrates by the Rieske nonheme mononuclear iron oxygenase MdpJ

Abstract

The Rieske nonheme mononuclear iron oxygenase MdpJ of the fuel oxygenate-degrading bacterial strain Aquincola tertiaricarbonis L108 has been described to attack short-chain tertiary alcohols via hydroxylation and desaturation reactions. Here, we demonstrate that also short-chain secondary alcohols can be transformed by MdpJ. Wild-type cells of strain L108 converted 2-propanol and 2-butanol to 1,2-propanediol and 3-buten-2-ol, respectively, whereas an mdpJ knockout mutant did not show such activity. In addition, wild-type cells converted 3-methyl-2-butanol and 3-pentanol to the corresponding desaturation products 3-methyl-3-buten-2-ol and 1-penten-3-ol, respectively. The enzymatic hydroxylation of 2-propanol resulted in an enantiomeric excess of about 70% for the (R)-enantiomer, indicating that this reaction was favored. Likewise, desaturation of (R)-2-butanol to 3-buten-2-ol was about 2.3-fold faster than conversion of the (S)-enantiomer. The biotechnological potential of MdpJ for the synthesis of enantiopure short-chain alcohols and diols as building block chemicals is discussed.

Fig 1

Degradation of 2-propanol and accumulation of metabolites in resting-cell experiments of A. tertiaricarbonis wild-type strain L108 (A) and mdpJ knockout strain L108 (ΔmdpJ) K24 (B). In the latter case, 1,2-propanediol was below the detection limit (10 μM) throughout the experiment. The sum of 2-propanol and metabolites represents the percentage of all analyzed 2-propanol-derived compounds (2-propanol, acetone, and 1,2-propanediol) relative to the initial substrate concentration.

Fig 2

GC-MS analysis of the (S)-2-phenylbutyryl derivatives of a racemic (RS)-1,2-propanediol standard, a pure (S)-1,2-propanediol standard, and a sample from a resting-cell experiment of A. tertiaricarbonis wild-type strain L108 incubated on 2-propanol. (A) Total ion chromatogram signals; (B) mass spectra of peaks occurring in the total ion chromatograms of the sample and the racemic standard at 37.9 min, representing the (S)-2-phenylbutyryl derivative of (R)-1,2-propanediol.

Fig 3

Degradation of racemic 2-butanol and accumulation of metabolites in resting-cell experiments of A. tertiaricarbonis wild-type strain L108 (A) and mdpJ knockout strain L108 (ΔmdpJ) K24 (B). In the latter case, 3-buten-2-ol and 3-buten-2-one were below the detection limit (2 μM) throughout the experiment.

Fig 4

Formation of 3-buten-2-ol from 2-butanol by resting cells of A. tertiaricarbonis wild-type strain L108 after application of pure enantiomers as the substrate.

Fig 5

Favored substrate and corresponding product enantiomers of MdpJ-catalyzed hydroxylation of 2-propanol to 1,2-propanediol and desaturation of 2-butanol to 3-buten-2-ol.