Structural basis for conservation in the CYP51 family

Abstract

Sterol 14α-demethylases (14DM) comprise the CYP51 cytochrome P450 genome family. The 14DM reaction is essential for the biosynthesis of sterols which are necessary for production of cellular membranes. This is the most widely distributed P450, being present in all biological kingdoms. From one kingdom to another the primary amino acid sequence identity usually ranges between 30 and 20%. In this minireview we describe the conservation of specific amino acids and the various CYP51 orthologs and indicate the roles that they may play in the structure/function of this monooxygenase. The prediction of the roles of different amino acids in 14DM is based on high resolution tertiary structures of these enzymes which set the stage for detailed understanding of the 14α-demethylase reaction and its selective, phyla-specific inhibition which is crucial for the design of potent inhibitors for treatment of infection by pathogenic microbes.

Figure 1. Multiple sequence alignment of the CYP51 family

The alignment was carried out using 185 CYP51 sequences and displays two protozoan (Trypanosoma brucei and Monosiga brevicollis), two animal (monkey and sea urchin), two plant (potato and pine tree) and two fungal family members (Aspergillus nidulans (filamentous) and Candida glabrata (yeast)). The residues identical in all sequenced eukaryotic CYP51s are marked with black triangles, the light grey triangles show the residues conserved in more than 99% sequences. The black circles mark the phyla-specific residues included in Table 1B.

Figure 2. Ribbon diagram of CYP51 from T. brucei

A. The residues identical in all eukaryotic CYP51s (black triangles in Figure 1) are labeled, the side chains are presented as stick models. B. Stereo view.

Figure 3. Three groups of conservation in sterol 14α-demethylase

A. Heme support. B. Hypothetical proton delivery route: ligand-free T. brucei CYP51 [3g1q]. The heme, iron coordinating C422 and the side chains of the residues that form H-bonds (green dashed lines) are shown as stick models. Three water molecules are presented as red spheres. C. Substrate binding cavity: T. cruzi CYP51 [3k10] with the modeled preferred substrate eburicol (magenta). Side chains of the family conserved and phyla-specific residues that are located within wan der Waals contacts (<4.5A) with eburicol are labeled. The backbone of the secondary structural elements (αB’/B’C loop, N-terminal parts of αC and αI, β1-4 with the preceding K’/β1-4 loop and the β4 hairpin) which form the binding cavity is displayed as ribbons. The substrate access channel location is marked with the blue arrow. Sterol rings are numbered.

Scheme 1

Sterol 14α-demethylase reaction