Molecular Engineering of Microsomal P450 2a-4 to a Stable, Water-Soluble Enzyme

Peptitergented P450 2a-4 (Pepti-P450), a water-soluble form of the mouse microsomal P450 2a-4, was genetically engineered and expressed in Escherichia coli. The NH2-terminal hydrophobic sequence (positions 2 to 19) of Pepti-P450 was replaced by a peptitergent PD1, amphipathic peptide consisting of 24 residues (C. E. Schafmeister, L. J. Miercke, and R. M. Stroud (1993) Science 262, 734-738). The expression level of Pepti-P450 (90,000 molecules/cell) was at least four times greater than that of wild-type P450 2a-4. Since Pepti-P450 was quite stable and was expressed as a peripheral membrane protein, it can be easily purified from the membrane fraction treated with Na2CO3 without using any detergents during the chromatographic steps. The purified Pepti-P450 retained the spectral and catalytic properties of the unmodified enzyme with a similar Km value for steroid 15α-hydroxylase activity (19.7 μM in comparison to 14.2 μM of the wildtype). Gel permeation chromatography showed that the purified Pepti-P450 in the detergent-free buffer was an oligomer with an approximate molecular mass of 450 kDa. The replacement of the hydrophobic anchor domain with an amphipathic helix such as peptitergent, therefore, may provide a general method for engineering membrane-bound P450s to soluble enzymes.