CYP261 enzymes from deep sea bacteria: A clue to conformational heterogeneity in cytochromes P450

We have explored the adaptation of the cytochromes P450 (P450) of deep-sea bacteria to high hydrostatic pressures. Strict conservation of the protein fold and functional importance of protein-bound water make P450 a unique subject for the studies of high-pressure adaptation. Earlier, we expressed and purified a fatty-acid binding P450 from the deep-sea bacteria Photobacterium profundum SS9 (CYP261C1). Here, we report purification and initial characterization of its mesophilic ortholog from the shallow-water P. profundum 3TCK (CYP261C2), as well as another piezophilic enzyme, CYP261D1, from deep-sea Moritella sp. PE36. Comparison of the three enzymes revealed a striking peculiarity of the piezophilic enzymes. Both CYP261C1 and CYP261D1 possess an apparent pressure-induced conformational toggle actuated at the pressures commensurate with the physiological pressure of habitation of the host bacteria. Furthermore, in contrast to CYP261C2, the piezophilic CYP261 enzymes may be chromatographically separated into two fractions with different properties, and different thermodynamic parameters of spin equilibrium in particular. According to our concept, the changes in the energy landscape that evolved in pressure-tolerant enzymes must stabilize the less-hydrated, closed conformers, which may be transient in the catalytic mechanisms of nonpiezophilic enzymes. The studies of enzymes of piezophiles should help unravel the mechanisms that control water access during the catalytic cycle.