Background: Thiol dioxygenation is catalyzed by enzymes specific for each substrate. Results: Kinetic, structural, and spectroscopic data describe an enzyme from P. aeruginosa that is a 3-mercaptopropionate dioxygenase with secondary cysteine dioxygenase activity. Conclusion: An arginine to glutamine switch and the absence of a cis-peptide bond correlate with substrate preference. Significance: Characterization of this enzyme deepens our understanding of substrate specificity in thiol dioxygenases.

No abstract

No abstract

Cysteine dioxygenase (CDO) is a non-heme mononuclear iron enzyme with unique structural features, namely an intramolecular thioether crosslink between cysteine 93 and tyrosine 157, and a disulfide between substrate L-cysteine and cysteine 164 in the entrance channel to the active site. We investigated how these posttranslational modifications affect catalysis through a kinetic, crystallographic and computational study. The enzyme kinetics of a C164S variant are identical to WT indicating that disulfide formation at C164 does not significantly impair access to the active site at physiological pH. However, at high pH the cysteine-tyrosine crosslink formation is enhanced in C164S. This supports the view that disulfide formation at position 164 can limit access to the active site. The C164S yielded crystal structures of unusual clarity in both resting state and with cysteine bound. Both show that the iron in the cysteine bound complex is a mixture of penta-and hexa-coordinate with a water molecule taking up the final site (60% occupancy), which is where dioxygen is believed to coordinate during turnover. The serine also displays stronger hydrogen bond interactions to a water bound to the amine of the substrate cysteine. However, the interactions between cysteine and iron appear unchanged. DFT calculations support this and show that WT and C164S have similar binding energies for the water molecule in the final site. This variant therefore provides evidence that WT also exists in this equilibrium between penta-and hexa-coordinate forms and presence of the sixth ligand does not strongly affect dioxygen binding.

The processing of polysaccharide-based polymer compounds represents a major challenge because these materials behave considerably different compared to their petro-based counterparts. Especially in the manufacture of thermoplastic starch (TPS)-polyester films by means of blown film extrusion, an increase in the natural material proportion generally leads to processing difficulties. In addition, higher TPS contents adversely affect mechanical material characteristics. The present study focuses on the effect of malic acid (MA) on processing parameters and on the quality of TPS/poly(butylene adipate-co-terephthalate) films. The MA enantiomers D(1) and L(-) as well as the racemate were applied at various concentrations (0.2, 0.4, and 0.8 wt %). Results indicate that the addition of racemic MA at concentrations of 0.2% and 0.4% significantly improved the processibility of TPS. Simultaneously, positive effects such as improved ductility and water sorption characteristics were found.