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Prof Gerald Richter 

Research Interests

Flavoproteins are ubiquitous proteins and are able to catalyse a wealth of reactions from electron transfer (redox reactions, radical formation) to adduct formation. The relevant biologically active cofactors are FAD and FMN. Most of these reactions are only possible within the protein environment which can for example stabilise a flavin radical for days whereas the free species in aqueous solution has a lifetime of μs. In different flavoproteins the chemically reactive moiety is the isoalloxazine ring system of flavin. The protein environment is therefore directing which reaction will occur.

Research in my laboratory is aimed at the elucidation of reaction mechanisms of enzymes, with a particular emphasis on light-dependent flavoproteins. We are investigating two different families of these proteins: the DNA photolyase family and the phototropin protein group. Investigating the reaction mechanisms of these enzymes provides an opportunity to understand the evolution of light-reactive molecular mechanisms in living organisms.

We could show that the primary process in blue light perception in plants is the formation of a covalent adduct between phototropin (LOV domains) and the cofactor FMN. This process is reversible and all our experimental data are consistent with a radical pair mechanism.

Photocycle of wild-type LOV domains. R denotes the ribityl side chain of FMN.  Radical pair mechanism for the formation of a C4a-adduct in phototropins.

Replacement of the native cofactor FMN with the analogue 5-deazaFMN resulted in a photosensitive protein that forms a stable photoproduct upon irradiation with blue light. The dark state can be regenerated by irradiation with UV light. We have thus created a photo-active nanoswitch.

UV/Vis spectra of a LOV domain containing 5-deazaFMN. Absorbance change upon irradiation with blue light (400 nm, left) and UV-B light (310 nm, right)

We are using different spectroscopic techniques in order to address the problem from as many directions as possible. Currently we are using NMR, EPR, ENDOR, Raman, and infrared spectroscopy. We have shown that reaction mechanisms could only be addressed reasonably using these techniques by labelling of proteins and co-factors with stable isotopes.

We have developed an enzymatic one-pot reaction for the synthesis of isotope-labelled flavins starting from labelled glucose and we are able to produce these labelled compounds in excellent yields.

One-pot synthesis of riboflavin: depending on the position of the C-label in glucose, are pair of labelled C-atoms (b – f) is obtained in the product.