Review Many facets of mammalian lanosterol 14a-demethylase from the evolutionarily conserved cytochrome P450 family CYP51 Nata  sa Debeljak, Martina Fink, and Damjana Rozman * Medical Center for Molecular Biology, Institute of Biochemistry, Faculty of Medicine, University of Ljubljana, Vrazov trg 2, SI-1000 Ljubljana, Slovenia Received 20 June 2002, and in revised form 19 July 2002 Abstract Lanosterol 14a-demethylase is a cytochrome P450 enzyme of the cholesterol biosynthetic pathway belonging to the CYP51 gene family which is the most evolutionarily conserved member of the CYP superfamily. Mammalian (human, mouse, rat, pig) CYP51 genes are unique in sharing several common characteristics: highly conserved exon/intron borders and proximal promoter struc- tures, ubiquitous expression at the highest level in the testis, and appearance of testis-specific transcripts that arise from differential polyadenylation site usage. CYP51 protein demethylates lanosterol to form follicular fluid meiosis-activating sterol, FF-MAS, which is, besides being an intermediate of cholesterol biosynthesis, also a signaling sterol that accumulates in ovaries. CYP51 protein resides in the endoplasmatic reticulum of most cells and also in acrosomal membranes of spermatids where transport through the Golgi apparatus is suggested. While sterol regulatory element binding protein (SREBP)-dependent transcriptional regulation of CYP51 contributes to synthesis of cholesterol, the germ-cell-specific cAMP/CREMs-dependent upregulation might contribute to increased production of MAS. Ó 2002 Elsevier Science (USA). All rights reserved. Keywords: Cytochrome P450; Cholesterol biosynthesis; Evolution; Meiosis-activating sterol; Sterol regulatory element binding protein Mammalian lanosterol 14a-demethylases are members of the evolutionary conserved CYP family Lanosterol 14a-demethylase belongs to the cyto- chrome P450 family number 51 and is accordingly named CYP51. It was first characterized in yeast Sac- charomyces cerevisiae and classified as CYP51 having a nomenclature number reserved for fungal P450s. It is the only cytochrome P450 family present in all king- doms of biology (Table 1) and is believed to be the an- cestor of all other P450 families [1–4]. The first example of orthologous P450s occurring in distinct kingdoms was reported in 1996, comparing yeast and rat CYP51s, both phyla having the 14a-demethylation function [5]. A year later the orthologous nature of plant CYP51 to fungal and animal CYP51s was confirmed [6] and the confirmation of an ortholog in bacteria followed as the bacterial CYP51 has been discovered [7,8]. The in vivo role of bacterial M. tuberculosis sterol 14a-demethylase remains unknown [8]. Sterol 14a-demethylase enzyme catalyzes the oxida- tive removal of the 14a-methyl group (C32) of lanosterol and 24-methylene-24,25-dihydrolanosterol in fungi, la- nosterol and 24,25-dihdrolanosterol in mammals, and obtusifoliol in plants (Fig. 1). Demethylation of sub- strates proceeds through three successive mono- oxygenations steps without releasing intermediates. The methyl group is in the first step converted to alcohol, then to an aldehyde and in the last step removed as formic acid (Fig. 2). Each step of mono-oxygenation requires one molecule of molecular oxygen and one molecule of NADPH [9]. Lanosterol 14a-demethylase is a class II enzyme requiring the FAD/FMN-containing NADPH-cytochrome P450 reductase as redox partner. The complex sterol 14-demethylation reaction presents one of the key steps in sterol biosynthesis, an essential metabolic pathway producing ergosterol in fungi, phy- tosterol in plants, and cholesterol in animals [10]. In addition to that, CYP51 also has a role in producing Archives of Biochemistry and Biophysics 409 (2003) 159–171 www.elsevier.com/locate/yabbi ABB * Corresponding author. Fax: +386-1-543-7641. E-mail address: damjana.rozman@mf.uni-lj.si (D. Rozman). 0003-9861/02/$ - see front matter Ó 2002 Elsevier Science (USA). All rights reserved. PII:S0003-9861(02)00418-6