Cytochrome P450(11 beta): structure-function relationship of the enzyme and its involvement in blood pressure regulation

Identification of functional consequence of a novel selection signature in CYP11b1 gene for milk fat content in Bubalus bubalis

Genomic selection for traits of economic importance is an emerging approach carrying tremendous potentials. Many of polygenic traits as milk fat, protein and yield have been characterize at genomic level and important selection signatures have been identified. Cytochrome P450 enzymes are potential loci for affecting many of dairy capabilities. Present study was conducted for genomic dissection of CYP11b1 gene in riverine buffaloes and seven genetic variations were identified. Out of these, one novel polymorphism (p.A313T) was found well associated with milk fat %age. AB genotyped buffaloes were found to have higher milk fat %age (8.9%) for this loci. p.A313T was further validated at larger data set by restriction digestion using CviAII enzyme. Functional consequences of this locus were also predicted by studying three dimensional structure of CYP11b1 protein. For this purpose, 3D protein model was predicted by homology modeling, secondary structural attributes were determined, signal peptide was predicted and a transmembrane helix was also identified. One of polymorphism (p.Y205L) was found in the vicinity of functionally significant F-G loop region, which is the part of protein gets attached to the inner mitochondrial membrane. But this variation could not be associated and needs further investigation. p.A30V, a popular selection marker in cattle, was found in buffaloes as well but could not be associated and might need further confirmation on larger data set. Results of this study illustrate the impending potential of this gene in determining dairy capabilities of buffaloes and might have a role in selection of superior dairy buffaloes.

Joint analysis of the influence of CYP11B1 and DGAT1 genetic variation on milk production, somatic cell score, conformation, reproduction, and productive lifespan in German Holstein cattle1

Recent publications indicate genetic variation in milk production traits on proximal BTA14, which cannot be explained solely with genetic variation in the DGAT1 gene. To elucidate these QTL effects, animals from a German Holstein granddaughter design (18 families, 1,291 sons) were genotyped for CYP11B1 (V30A) and DGAT1 (K232A) polymorphisms. Frequencies of alleles of maternal descent were estimated for CYP11B1(V) (0.776) and DGAT1(K) (0.549). Allele substitution effects (alpha/2) were first calculated for both alleles in separate models and then in a joint model. From the joint analysis, CYP11B1(V) effects on fat content (+0.04%) and protein content (+0.01%) were positive. Effects on milk yield (-82 kg), fat yield (-0.5 kg), and protein yield (-1.9 kg) were negative. Compared with the individual analysis, DGAT1(K) effects on fat content (+0.28%), protein content (+0.06%), and milk yield (-258 kg) were reduced; fat yield (+10.8 kg) was enhanced; and protein yield (-3.8 kg) was reduced. In the joint analysis, allele substitution effects of CYP11B1(V) and DGAT1(K) together explained more of the variation in milk production traits than DGAT1(K) alone. Further significant effects were found for CYP11B1(V) and DGAT1(K) among 6 reproduction traits and 14 conformational traits. These observations indicate a possible negative influence of DGAT1(K) on maternal nonreturn rate, and thus, on length of productive life.

Deficiência da 11beta-hidroxilase

A hiperplasia congênita da adrenal devido à deficiência da enzima 11beta-hidroxilase é resultado de uma falha na conversão do 11-desoxicortisol em cortisol na última etapa da via sintética dos glicocorticóides. Em geral, esta forma da doença é responsável por cerca de 5% dos casos. A manifestação clínica do excesso de andrógenos em pacientes do sexo feminino inclui graus de ambigüidade genital que podem variar entre uma clitoromegalia até a virilização completa da genitália. Devido ao acúmulo de mineralocorticóides, aproximadamente 50% dos pacientes desenvolvem hipertensão arterial. Mutações no gene CYP11B1, que codifica a enzima 11beta-hidroxilase, são responsáveis pela doença. As características bioquímicas e moleculares da enzima e suas implicações na apresentação clínica da deficiência da 11beta-hidroxilase são abordadas no presente trabalho de revisão.

Paralogues of porcine aromatase cytochrome P450: a novel hydroxylase activity is associated with the survival of a duplicated gene

The gonadal and placental paralogues of porcine aromatase cytochrome P450 (P450arom) were examined for novel catalytic properties to shed light on the evolutionary survival of duplicated copies of an enzyme critical to reproduction. Recombinant gonadal P450arom catalyzed the formation of a novel metabolite from testosterone, identified by gas chromatography/mass spectrometry and biochemical analyses as 1 beta-hydroxytestosterone (1 beta OH-T), in almost equal proportion to 17beta-estradiol (E(2)). This activity was absent in reactions with the porcine placental paralogue (or other orthologues) of P450arom and was minimal with androstenedione. Incubations with both porcine enzymes and with bovine and human P450arom demonstrated that 1 beta OH-T was not aromatizable, and 1 beta OH-T activated the androgen receptor of prostate cancer cells in vitro. Porcine testicular and follicular granulosa tissues synthesized 1 beta OH-T, which was also detected in testicular venous plasma. These results constitute the first of identification of a novel, perhaps potent, nonaromatizable metabolite of testosterone, whose synthesis (paradoxically) can be definitively ascribed to the activity of the gonadal paralogue of porcine P450arom. It probably represents an evolutionary gain of function associated with fixation and the survival of the genes after CYP19 duplication. Novel activities and adaptive functions may exist among other duplicated vertebrate aromatases.

Analyses of the CYP11B gene family in the guinea pig suggest the existence of a primordial CYP11B gene with aldosterone synthase activity

In this study we describe the isolation of three genes of the CYP11B family of the guinea pig. CYP11B1 codes for the previously described 11beta-hydroxylase [Bülow, H.E.,Möbius, K., Bähr, V. & Bernhardt, R. (1996) Biochem. Biophys. Res. Commun. 221, 304-312] while CYP11B2 represents the aldosterone synthase gene. As no expression for CYP11B3 was detected this gene might represent a pseudogene. Transient transfection assays show higher substrate specificity for its proper substrate for CYP11B1 as compared to CYP11B2, which could account for the zone-specific synthesis of mineralocorticoids and glucocorticoids, respectively. Thus, CYP11B2 displayed a fourfold higher ability to perform 11beta-hydroxylation of androstenedione than CYP11B1, while this difference is diminished with the size of the C17 substituent of the substrate. Furthermore, analyses with the electron transfer protein adrenodoxin indicate differential sensitivity of CYP11B1 and CYP11B2 as well as the three hydroxylation steps catalysed by CYP11B2 to the availability of reducing equivalents. Together, both mechanisms point to novel protein intrinsic modalities to achieve tissue-specific production of mineralocorticoids and glucocorticoids in the guinea pig. In addition, we conducted phylogenetic analyses. These experiments suggest that a common CYP11B ancestor gene that possessed both 11beta-hydroxylase and aldosterone synthase activity underwent a gene duplication event before or shortly after the mammalian radiation with subsequent independent evolution of the system in different lines. Thus, a differential mineralocorticoid and glucocorticoid synthesis might be an exclusive achievement of mammals.

Bilateral laparoscopic adrenalectomy for congenital adrenal hyperplasia with severe hypertension, resulting from two novel mutations in splice donor sites of CYP11B1

We present an in vivo and in vitro study of congenital adrenal hyperplasia in a patient with 11beta-hydroxylase deficiency. Sequencing of the CYP11B1 gene showed two new base substitutions, a conservative 954 G-->C transversion at the last base of exon 5 (T318T), and a IVS8 + 4A-->G transition in intron 8. In addition, two polymorphisms were found in exons 1 and 2. The genetically female patient was raised as a male because of severe pseudohermaphroditism. Glucocorticoid-suppressive treatment encountered difficulties in equilibration and compliance, resulting in uncontrolled hypertension with pronounced hypertrophic cardiomyopathy. At 42 yr of age the occurrence of central retinal vein occlusion with permanent loss of left eye vision led to the decision to perform bilateral laparoscopic adrenalectomy. Surgery was followed by normalization of blood pressure and good compliance with glucocorticoid and androgen substitutive therapies. In vitro, adrenal cells in culture and isolated mitochondria showed extremely low 11beta-hydroxylase activity. Analysis of adrenal CYP11B1 messenger ribonucleic acid (mRNA) by RT-PCR and sequencing showed the expression of a shorter mRNA that lacked exon 8 and did not contain either the exon 5 mutation or the exon 1 and 2 polymorphisms. This suggested that one CYP11B1 allele carried the intron 8 mutation, responsible for skipping exon 8. The other allele carried the exon 5 mutation, and its mRNA was not detectable. Western blot analysis showed weak expression of a shorter CYP11B immunoreactive band of 43 kDa, consistent with truncation of exon 8. Thus, bilateral adrenalectomy in this patient allowed effective treatment of severe hypertension and helped in understanding the mechanisms and physiopathological consequences of two novel mutations of CYP11B1.

Late steps of aldosterone biosynthesis: sheep are not rats

1. The last three steps of aldosterone biosynthesis have been demonstrated to be catalysed by a single enzyme, referred to as CYP11B (or P450(11) beta) in cow, pig, sheep and bullfrog and as CYP11B2 (or P450aldo) in rat, human, mouse and hamster. 2. The related enzyme CYP11B1 (also referred to as P450(11) beta) in rat, human, mouse and hamster does not have aldosterone synthesis activity, but no such enzyme has been reported in the cow, pig or sheep to date. 3. Exclusive aldosterone secretion in the zona glomerulosa (ZG) of the adrenal cortex in species such as rat, human, mouse and hamster could be ascribed to the restricted distribution of CYP11B2 to the same region in the adrenal cortex. 4. In other species, such as cow, pig and sheep, the CYP11B enzyme is expressed throughout the adrenal cortex and, thus, the exclusive aldosterone biosynthesis in the ZG could not be explained simply by the distribution of the enzyme. 5. We have shown in the sheep that potassium loading and acute sodium depletion stimulate the CYP11B transcript levels, which are not further increased by chronic sodium depletion. 6. The predominant CYP11B in the sheep adrenal cortex catalyses the synthesis of aldosterone from deoxycorticosterone (DOC) in vitro, is expressed throughout the adrenal cortex and the corresponding transcript levels are increased by K+ loading or sodium depletion. In short, as far as the last step of aldosterone biosynthesis is concerned, sheep are different from rats. In the rat, the CYP11B2 transcript or protein is elevated by K+ loading or sodium depletion, but not the CYP11B1 transcript or protein. 7. We propose that during severe sodium deficiency there is a switch in the aldosterone pathway to one preferentially involving 18-OH-DOC and not corticosterone.

The microsomal mixed function oxidase system of amphibians and reptiles: components, activities and induction

This article reviews current research in amphibian and reptilian cytochromes P450, important to the overall understanding of xenobiotic metabolism in the ecosystem and the evolution of P450s. Amphibians and reptilians contain the normal mixed function oxidase system (MFO). In general the MFO content and activities are less than those found in mammals, but only a few of the known activities have been examined in these vertebrate classes. Research to date has focused on two families of cytochromes P450, CYP1 and 2. The isoforms examined catalyze the classic activities but there have been notable absences. The total number of isoforms present and the breadth of substrates metabolized are yet unknown. Induction by foreign compounds (xenobiotics) is lengthier and yields lower levels of induced activity than is typically found in mammals. When these animals are pretreated with 3-methylcholanthrene (3MC) and beta-naphthaflavone (BNF), which are known to induce the same isoform in mammals, multiple isoforms are induced with different activities. Phenobarbital-pretreatment in turtles and alligators induces cytochromes P450 and suggestive data indicates induction in the lizard Agama lizard and the newt Pleurodeles waltl. In amphibians and reptiles a CYP2B protein does appear to be present along with constitutive activities associated with the 2 family of cytochromes P450. The markedly different response to classic inducers combined with lower or absent activities alters the view of how amphibians and reptilians respond to xenobiotic challenges.

Cytochrome P450(11 beta): ectopic expression in oocyte and its physiological implication

Cytochrome P450(11 beta) (steroid 11 beta-hydroxylase) catalyzes an essential step for biosynthesis of glucocorticoid as well as mineralocorticoid, and therefore is believed to exist specifically in the adrenocortical mitochondria. We previously isolated a complementary DNA clone encoding this enzyme from bullfrog (Rana catesbeiana) adrenal tissues and characterized the enzyme expressed in COS cells. To explore the tissue distribution of the enzyme we performed Northern blot analysis. Unexpectedly we found that a large amount of the mRNA exists in the ovary as well as the adrenal gland. It was present in oocytes, but not in follicular cells. The P450 protein was not found during early stages of oocyte development, and at the final stage of maturation the message appeared to be translated. Evidence was obtained that the stage-dependent translation of the mRNA was due to the regulated polyadenylation at its 3'-end. In oocytes of various organisms several maternal mRNAs are known to add poly(A) tails in the cytoplasm during the progesterone-induced maturation.