Decoding of the cytochrome P450 monooxygenase CYP4B1 by biochemical, evolutional, and structural analysis

• Applicants: Dr. Marco Girhard; Dr. Constanze Wiek
• Subject Area: Biochemistry
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 465450790

The cytochrome P450 family 4 is one of the oldest P450 enzyme families; the enzymes have been highly conserved throughout evolution. Among all these different enzymes, the topic of this grant application, the monooxygenase CYP4B1, is a special and unique enzyme for the following reason: No substrate has been found for the native human CYP4B1 enzyme so far, thus qualifying it as an ‘orphan’ P450 enzyme. The apparent absence of catalytic activity of the human CYP4B1 can partially be attributed to a single amino acid change in the so-called meander region of the enzymes active centre: The native human CYP4B1 has a serine at position 427, whereas all other CYP4B1 enzymes (and also all CYP4 family members in mammals) have proline at the corresponding positions.Strikingly, the situation is completely different in various mammals such as cows, horses, dogs, rats, rabbits or mice. Here, CYP4B1 acts at the interface between endobiotic and xenobiotic metabolism: Besides ω-hydroxylation of unsaturated fatty acids, CYP4B1 is specifically responsible (in contrast to other CYP4 family members) to bioactivate of a range of xenobiotics including 4-ipomeanol and perilla ketone.However, previous data published by the applicants as well as unpublished preliminary data reveals a much more complex situation: During evolution, genetic changes at distinct positions in CYP4B1 in human subpopulations, human ancestors (Denisovan) and in great apes (chimps) greatly diminished or abolished the enzymatic activity of CYP4B1.Based on the successful collaboration between the HNO Clinic and the Institute of Biochemistry, the main objective of the project is to decode the physiological importance of CYP4B1 during evolution in different organisms and species, and to test the hypothesis that in humans and great apes/primates other P450s have taken over functions of CYP4B1. In order to reach this goal, three mutually supporting approaches will be undertaken: (i) Functional aspects of CYP4B1-mediated metabolism will be investigated aiming to find novel substrates for CYP4B1. (ii) The applicants will shed light on evolutionary development of CYP4B1 and precisely pinpoint the time-line at which losses of CYP4B1 functions occurred. Alongside, evolutionary compensation for lost CYP4B1 functions will be investigated by elucidating whether other cytochrome P450 monooxygenases can compensate for lost CYP4B1 functions. (iii) Finally, structural aspects of CYP4B1 interaction with substrates and inhibitors will be investigated to complement and explain the results of the functional and evolutionary investigations.The teams of this tandem project have all the necessary expertise and collaborators to profoundly analyse the described various aspects of this orphan CYP4B1 and finally decode its physiological function(s).

• DFG Programme: Research Grants
• Co-Investigator: Privatdozent Dr. Michael Hutter