Crystal structure of human cytochrome P450 2D6.

Cytochrome P450 2D6 is a heme-containing enzyme that is responsible for the metabolism of at least 20% of known drugs. Substrates of 2D6 typically contain a basic nitrogen and a planar aromatic ring. The crystal structure of human 2D6 has been solved and refined to 3.0A resolution. The structure shows the characteristic P450 fold as seen in other members of the family, with the lengths and orientations of the individual secondary structural elements being very similar to those seen in 2C9. There are, however, several important differences, the most notable involving the F helix, the F-G loop, the B'helix, beta sheet 4, and part of beta sheet 1, all of which are situated on the distal face of the protein. The 2D6 structure has a well defined active site cavity above the heme group, containing many important residues that have been implicated in substrate recognition and binding, including Asp-301, Glu-216, Phe-483, and Phe-120. The crystal structure helps to explain how Asp-301, Glu-216, and Phe-483 can act as substrate binding residues and suggests that the role of Phe-120 is to control the orientation of the aromatic ring found in most substrates with respect to the heme. The structure has been compared with published homology models and has been used to explain much of the reported site-directed mutagenesis data and help understand the metabolism of several compounds.

Potential of real-time measurement of GFP-fusion proteins.

Building on the basic design concepts of Randers-Eichhorn [Biotechnol. Bioeng. 55 (1997) 921], an on-line, real-time robust, steam sterilisable optical sensor for monitoring green fluorescent protein (GFP) has been developed. A general cloning vector for fusion expression proteins was constructed, allowing expression of both GFP and the target protein as a fusion. Cultivations were carried out at the 20l scale with the signal from the sensor being relayed directly to the control system of the bioreactors. The production of GFP was then measured on-line, the signal was interfaced directly with other controlling parameters, thereby allowing the microbial process to be controlled directly based on recombinant protein expression. A positive expression correlation between on-line and off-line data was obtained. Protein accretion measured off-line was quantified using both LC-MS and plate reader assays. The potential of such a sensor for many aspects of process development is considerable and we have developed a working system which allows the optimisation of production conditions, for example, linking pH control directly to the fusion protein. Results are also presented that illustrate GFP does not alter the cultivation characteristics of the target protein when compared to the native construct. Whether GFP expressed as a fusion influences the solubility of the target protein is also discussed.