Peptide alignment of the porcine 21-hydroxylase cytochrome P-450 using a cDNA sequence of the corresponding bovine enzyme

The P450 superfamily: update on new sequences, gene mapping, accession numbers, early trivial names of enzymes, and nomenclature

We provide here a list of 221 P450 genes and 12 putative pseudogenes that have been characterized as of December 14, 1992. These genes have been described in 31 eukaryotes (including 11 mammalian and 3 plant species) and 11 prokaryotes. Of 36 gene families so far described, 12 families exist in all mammals examined to date. These 12 families comprise 22 mammalian subfamilies, of which 17 and 15 have been mapped in the human and mouse genome, respectively. To date, each subfamily appears to represent a cluster of tightly linked genes. This revision supersedes the previous updates [Nebert et al., DNA 6, 1-11, 1987; Nebert et al., DNA 8, 1-13, 1989; Nebert et al., DNA Cell Biol. 10, 1-14 (1991)] in which a nomenclature system, based on divergent evolution of the superfamily, has been described. For the gene and cDNA, we recommend that the italicized root symbol "CYP" for human ("Cyp" for mouse), representing "cytochrome P450," be followed by an Arabic number denoting the family, a letter designating the subfamily (when two or more exist), and an Arabic numeral representing the individual gene within the subfamily. A hyphen should precede the final number in mouse genes. "P" ("p" in mouse) after the gene number denotes a pseudogene. If a gene is the sole member of a family, the subfamily letter and gene number need not be included. We suggest that the human nomenclature system be used for all species other than mouse. The mRNA and enzyme in all species (including mouse) should include all capital letters, without italics or hyphens. This nomenclature system is identical to that proposed in our 1991 update. Also included in this update is a listing of available data base accession numbers for P450 DNA and protein sequences. We also discuss the likelihood that this ancient gene superfamily has existed for more than 3.5 billion years, and that the rate of P450 gene evolution appears to be quite nonlinear. Finally, we describe P450 genes that have been detected by expressed sequence tags (ESTs), as well as the relationship between the P450 and the nitric oxide synthase gene superfamilies, as a likely example of convergent evolution.

Nucleotide sequence analysis of murine 21-hydroxylase genes: mutations affecting gene expression

Steroid 21-hydroxylase [21-OHase; steroid 21-monooxygenase; steroid, hydrogen-donor:oxygen oxidoreductase (21-hydroxylating); EC 1.14.99.10] is a cytochrome P-450 enzyme required for the adrenal synthesis of mineralocorticoids and glucocorticoids. The gene encoding this protein is present in two copies (21-OHase A and B) in the S region of the murine major histocompatibility complex. Previous studies utilizing gene-specific oligonucleotide probes and gene transfer showed that only the 21-OHase A gene is expressed in the BALB/c mouse. Here, we present the complete primary structures of both BALB/c 21-OHase encoding genes. Comparison of the nucleotide sequences defines a deletion of 215 nucleotides spanning the second exon of the 21-OHase B gene; other nucleotide changes in the 21-OHase B gene introduce frame shifts and premature termination codons. Southern blot analysis of C57BL/6 and DBA/2J mice indicates that a similar deletion is present in these strains; however the C3H/HeJ strain is a structural variant. A hybrid gene composed of the 21-OHase B promoter placed 5' of the 21-OHase A structural sequences was efficiently transcribed following transfection into Y1 adrenocortical tumor cells. These findings demonstrate that the 21-OHase B gene promoter is functional and suggest that mutations within the 21-OHase B structural gene are responsible for its lack of expression.

Structure of human steroid 21-hydroxylase genes

We have determined the structure of cDNA and two genomic genes encoding steroid 21-hydroxylase [21-OHase; steroid 21-monooxygenase; steroid, hydrogen-donor:oxygen oxidoreductase (21-hydroxylating); EC 1.14.99.10]. If this cytochrome P-450 enzyme is defective, cortisol cannot be synthesized, resulting in congenital adrenal hyperplasia. The cDNA encoding this enzyme is 2.0 kilobases long, and the encoded protein is predicted to contain 494 amino acid residues with a molecular weight of 55,000. This enzyme is at most 28% homologous to other P-450 enzymes that have been studied. The 21-OHase genomic genes, which are located in the HLA major histocompatibility complex on chromosome 6, each contain 10 exons. This structure is distinct from other characterized P-450 genes, which contain 7 or 9 exons. Studies of individuals with homozygous deletions of the 21-OHase A or B genes suggest that only the B gene encodes an active enzyme. This is confirmed by the finding that the A gene has an 8-base deletion within codons 110-112, resulting in a frameshift that brings a stop codon into the reading frame at codon 130. A second frameshift and a nonsense mutation occur downstream. In contrast, the sequence of the exons of the B gene is identical to the cDNA sequence. The 21-OHase A gene is, therefore, a pseudogene.

Bovine steroid 21-hydroxylase: regulation of biosynthesis

A recombinant cDNA clone, PBC21-1, specific for bovine steroid 21-hydroxylase cytochrome P-450 (P-450C21) was identified in a bovine adrenocortical cDNA library, and this identity was confirmed by nucleotide sequencing which revealed significant amino acid homology (77%) with human P-450C21 cDNA. The pBC21-1 insert is 1.7 kilobases in length and includes a 1128 base pair region that encodes the C-terminal 376 amino acids of bovine P-450C21 as well as 535 base pairs of 3'-untranslated sequence. A novel feature of this insert is a 20 base pair intervening sequence near the 5' end, apparently the result of an aberrant splicing event. Northern blot analysis reveals that bovine P-450C21 is encoded by two transcripts, 2.3 and 2.0 kilobases in length which are detected in adrenal cortical RNA. Bovine liver, heart, kidney, and corpus luteum do not contain detectable P-450C21 transcripts. Regulation of P-450C21 gene expression by adrenocorticotropin was investigated with pBC21-1 and bovine adrenocortical cells in primary, monolayer culture. Treatment with ACTH or analogues of cAMP increases the steady-state levels of P-450C21 RNA in such cell cultures. In vitro transcription run-on assays suggest that this increase is, at least in part, due to the enhanced transcriptional activity of the P-450C21 gene.

Cloning and characterization of the bovine gene for steroid 21-hydroxylase (P-450c21)

Steroid 21-hydroxylase activity is required for the synthesis of both cortisol and aldosterone. Using two manually synthesized oligonucleotide probes, we screened a bovine genomic DNA library and identified a phage, lambda E11, carrying the gene for the steroid 21-hydroxylase, P-450c21. The identity of lambda E11 was initially proven by initiating dideoxy sequencing from the two oligonucleotides directly on the full-length, uncleaved phage template. Hybridization of total bovine genomic DNA to lambda E11 restriction fragments indicates the presence of repetitive sequences in or near the P-450c21 gene. Northern blots indicate that the mature mRNA exists in two principal forms of about 2.2 and 2.4 kb in length. Southern blots indicate there are two copies of the gene in the bovine genome. Sequence analysis of a 1141-bp Eco RI fragment of the gene shows three complete exons and a portion of a fourth exon, correctly determining the amino acid sequence of 148 amino acids of this important enzyme. This cloned 1141-bp fragment cross-hybridizes to human genomic DNA, indicating it should be a useful probe for studying the human P-450c21 gene in patients having impaired 21-hydroxylase activity.