A combinatorial approach to substrate discrimination in the P450 CYP1A subfamily.

A comparison of all known mammalian CYP1A sequences identifies nineteen sequence regions that are conserved within all 1A1s or within all 1A2s but at the same time systematically differ between any 1A1 and any 1A2. The purpose of this study was to explore links between these specific CYP1A sequence signatures and substrate specificity shift through the kinetic analysis of combinatorial variants of increasing complexity. The less complex variants correspond to multiple mutations within a short segment of their sequence. The more complex variants correspond to mosaic P450s recombining 1A1 and 1A2 sequences (up to 5 crossovers per sequence). Fifty-eight such functional CYP1A variants and parental wild-type enzymes were expressed in yeast and assayed with 7-alkoxyresorufins and ethoxyflurorescein ethyl ester as substrates. Observed kinetic data were analyzed by multivariate statistical analyses and hierarchical clustering in order to highlight correlations and identify potential sequence-activity relationships within the three-dimensional function space investigated. Several variants are outliers in these representations and show a redistribution of their substrate specificity compared to wild-type CYP1As. Some combinations of sequence elements were identified that significantly discriminate between 1A1 and 1A2 for these three substrates. The comparison of this combinatorial approach with previous results of site-directed mutagenesis is discussed.