Structure and reaction mechanism of benzylsuccinate synthase and its activating enzyme

All known organisms capable of anaerobic toluene metabolism initiate this pathway by addition of the methyl group of toluene to a fumarate cosubstrate to yield (R)-benzylsuccinate. This reaction represents a new biochemical principle and is catalysed by a glycyl-radical-enzyme, benzylsuccinate synthase (BSS). This enzyme has since become a model for enzymes catalysing analogous fumarate additions in anaerobic metabolic pathways of other hydrocarbons, including alkanes. Benzylsuccinate synthase contains a free radical on a conserved glycine residue, which is inserted by a separate, S-adenosylmethionine- dependent activating enzyme. The catalytic mechanism is proposed to involve the formation of an enzyme-bound substrate-radical from toluene, which then reacts with fumarate to a product-radical. Unlike other known glycyl-radical-enzymes, BSS contains additional subunits and [Fe4S4]-clusters whose functions are not yet understood. This proposal is intended to investigate the structure-function relationship of the benzylsuccinate synthase reaction mechanism and follows the following major aims: [1] solving the crystal structure of non-activated recombinant benzylsuccinate synthase. We have already attained a resolvation of the structure at 3.4 Ǻ, which promises to yield the elucidation of the structure during the next funding period. [2] further investigations on the reaction mechanism of BSS, providing a model for similar enzymes involved in anaerobic catabolism of other hydrocarbons, and [3] crystallising and characterising the activating enzyme and the activation reaction.

DFG-Verfahren Schwerpunktprogramme

Teilprojekt zu SPP 1319:  Biological Transformations of Hydrocarbons in the Absence of Oxygen