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The linker region of multi-domain enzymes has a very important role for the interconnection of different enzyme modules and for the efficiency of catalytic activity. This is particularly evident for artificial chimeric systems. We characterised an artificial self-sufficient enzyme developed by genetic fusion of the catalytic domain of cytochrome P450 3A4 and reductase domain of Bacillus megaterium BM3 (BMR). Here we report the direct electrochemistry of 3A4-BMR chimeras immobilised on glassy carbon electrodes and we investigated the effect of inter-domain loop length and immobilising environment flexibility on both redox properties and electrocatalysis. We observe that redox potential can be modulated by the linker length and the immobilising layer flexibility. In addition, enzyme inter-domain dynamics and environment flexibility also modulate 3A4-BMR turnover efficiency on electrode system. V max values are increased up to about 100% in the presence of testosterone and up to about 50% in presence of tamoxifen by decreasing immobilising film rigidity. The effect on 3A4-BMR V max values is dependent on inter-domain loop length with 3A4-5GLY-BMR chimera being the more affected. The underlying reason for these observations is the potential motion of the FMN domain that is the key to shuttle electrons from FAD to haem., (Copyright © 2018 Elsevier Inc. All rights reserved.)

In order to develop in vitro methods as an alternative to P450 animal testing in the drug discovery process, two main requisites are necessary: 1) gathering of data on animal homologues of the human P450 enzymes, currently very limited, and 2) bypassing the requirement for both the P450 reductase and the expensive cofactor NADPH. In this work, P450 2C20 from Macaca fascicularis, homologue of the human P450 2C8 has been taken as a model system to develop such an alternative in vitro method by two different approaches. In the first approach called "molecular Lego", a soluble self-sufficient chimera was generated by fusing the P450 2C20 domain with the reductase domain of cytochrome P450 BM3 from Bacillus megaterium (P450 2C20/BMR). In the second approach, the need for the redox partner and also NADPH were both obviated by the direct immobilization of the P450 2C20 on glassy carbon and gold electrodes. Both systems were then compared to those obtained from the reconstituted P450 2C20 monooxygenase in presence of the human P450 reductase and NADPH using paclitaxel and amodiaquine, two typical drug substrates of the human P450 2C8. The K(M) values calculated for the 2C20 and 2C20/BMR in solution and for 2C20 immobilized on electrodes modified with gold nanoparticles were 1.9 ± 0.2, 5.9 ± 2.3, 3.0 ± 0.5 μM for paclitaxel and 1.2 ± 0.2, 1.6±0.2 and 1.4 ± 0.2 μM for amodiaquine, respectively. The data obtained not only show that the engineering of M. fascicularis did not affect its catalytic properties but also are consistent with K(M) values measured for the microsomal human P450 2C8 and therefore show the feasibility of developing alternative in vitro animal tests., (Copyright © 2012 Elsevier Inc. All rights reserved.)