Lena_Appel.jpg

Class II benzoyl-CoA reductases

Carola_Seelmann.jpeg

Hi, I am Lena

 

in strictly anaerobic bacteria, a giant metalloenzyme machinery catalyzses the key step of anaerobic degradation, the dearomatization of the central intermediate benzoyl-CoA a cyclic diene. This machinery, referred to as class II benzoyl-CoA reductase (BCR) complex uses electron bifurcation, the coupling of endergonic to exergonic redox reactions, to achieve the mechanistically highly demanding reductive dearomatization of the benzene ring. It fundamentally differs from the ATP-dependent class I benzoyl-CoA reductases, and harbors tungsopterin the active site, and more than 50 further redox cofactors. Despite its crucial role in the anaerobic degradation of aromatic compounds, many aspects regarding the structura and function have remained unclear. I aim to unravel the secrets that this metalloenzyme machinery still holds for us by a number of techniques including cryo-electron microscopy with collaboration partners at the Max-Planck-Institute of Biophysics in Frankfurt.

                                                                                      Hi, I am Carola.

I am interested in BamB, the active site subunit of the class II benzoyl-CoA reductase complex from the Fe(III)-respiring Geobacter metallireducens. The dearomatization of benzoyl-CoA to a cyclic dienoyl-CoA is accomplished at a unique tungsten cofactor (Wco) of BamB, the redox potential of the difficult reaction is with E°' = -622 mV below the biological redox window.

So far, the mechanism of benzoyl-CoA reduction by class II benzoyl-CoA reductases is still enigmatic. To elucidate this reaction, I am homologously producing molecular variants of BamB to characterize them spectroscopically, e.g. via electron paramagnetic resonance spectroscopy. The biosynthesis and BamB maturation are also largely unknown and require a number of protein components including a special chaperone. To investigate these open questions, I am heterologously producing and enriching several candidate proteins to determine their respective roles in suitable in-vitro maturation assays.

BCRII_LA_Figure.png

Proposed architecture of the benzoyl-CoA reductase complex, and its interaction with membrane components

BamBC_Carola.tif

Left: structure of the the catalytic BamB subunit (red) together with BamC ( green). Right: W-cofactor, [4Fe-4S] cluster and the substrate benzoyl-CoA.