Johann Heider

Research area

We are interested in the biochemistry of anaerobic hydrocarbon metabolism. All enzymic reactions involving initial attack at hydrocarbons in the absence of oxygen must be expected to follow some unusual biochemical principles, because these substrates are only turned over by oxygen-dependent mono- or dioxygenases aerobically. In particular, we study two new reaction principles of hydrocarbon-metabolism, namely fumarate addition and oxygen-independent hydroxylation. The first reaction is involved in anaerobic toluene degradation and catalyses the stereospecific formation of (R)-benzylsuccinate from toluene and fumarate by a novel glycyl radical enzyme, benzylsuccinate synthase. The second reaction initiates anaerobic ethylbenzene degradation and catalyses the stereospecific hydroxylation of ethylbenzene to (S)-1-phenylethanol by a new molybdenum enzyme. Moreover, we are characterizing the other enzymes involved in the respective pathways, which include a novel ketone carboxylase or enzymes of a beta-oxidation pathway. We are interested in identifying the respective reaction mechanisms as well as in utilizing these new reactions for biotechnological purposes.

 

Research project within SYNMIKRO

(R)-benzylsuccinate is the first intermediate of anaerobic toluene degradation and also has some potential as building block for biodegradable (co)polymers or for pharmaceuticals. Because its chemical synthesis is rather expensive, we try to exploit the enzymes of anaerobic toluene degradation to set up a bacterial production strain for (R)-benzylsuccinate. To achieve that, we will make use of the fully reversible pathway of beta-oxidation of benzylsuccinate to benzoyl-CoA, as catalyzed by five consecutive enzymes. This should yield to a novel synthetic metabolic pathway that makes use of the normal E. coli fermentation product succinate and condenses it with benzoyl-CoA and then is further converted to (R)-benzylsuccinate. The second substrate will be fed to the cells in the form of benzoate, which will have to be taken up and activated to the CoA thioester. Therefore, we have initially constructed a recombinant bacterial strain capable of converting exogenous benzoate to benzoyl-CoA and feeding it into the biosynthetic pathway of the plant polyketide 3,5-dihydroxybiphenyl. We actually succeeded in producing a secondary metabolite in Escherichia blattae containing the genes coding for a benzoate transporter, a benzoate-CoA ligase and the plant enzyme for biphenyl synthesis. This strain will now be the basis for establishing the reverse beta-oxidation pathway for benzylsuccinate synthesis.