Genetic variations in NADPH-CYP450 oxidoreductase in a Czech Slavic cohort

POR polymorphisms are associated with 21 hydroxylase deficiency

PURPOSE

Genotype-phenotype correlation in congenital 21 hydroxylase deficiency is strong but by no means absolute. Indeed, clinical and hormonal features may vary among patients carrying similar CYP21A2 mutations, suggesting that modifier genes may contribute to the phenotype. Aim of the present study was to evaluate whether polymorphisms in the p450  oxidoreductase (POR) gene may affect clinical features in patients with 21 hydroxylase deficiency METHODS: Sequencing of the POR gene was performed in 96 patients with 21 hydroxylase deficiency (49 classic, 47 non-classic) and 43 control subjects.

RESULTS

Prevalence of POR polymorphisms in patients with 21 hydroxylase was comparable to controls and known databases. The rs2228104 polymorphism was more frequently associated with non-classic vs classic 21 hydroxylase deficiency (allelic risk 7.09; 95% C.I. 1.4-29.5, p < 0.05). Classic 21 hydroxylase-deficient carriers of the minor allele in the rs2286822/rs2286823 haplotype presented more frequently the salt-wasting form (allelic risk 1.375; 95% C.I. 1.138-1.137), more severe Prader stage at birth (allelic risk 3.85; 95% C.I. 3.78-3.92), higher ACTH levels, and younger age at diagnosis.

CONCLUSIONS

Polymorphisms in the POR gene are associated with clinical features of 21 hydroxylase deficiency both as regards predisposition to classic vs non-classic forms and severity of classic adrenal hyperplasia.

Insight into the structural and functional analysis of the impact of missense mutation on cytochrome P450 oxidoreductase

Cytochrome P450 oxidoreductase (POR) is a steroidogenic and drug-metabolizing enzyme. It helps in the NADPH dependent transfer of electrons to cytochrome P450 (CYP) enzymes for their biological activity. In this study, we employed integrative computational approaches to decipher the impact of proline to leucine missense mutation at position 384 (P384L) in the connecting/hinge domain region which is essential for the catalytic activity of POR. Analysis of protein stability using DUET, MUpro, CUPSAT, I-Mutant2.0, iStable and SAAFEC servers predicted that mutation might alter the structural stability of POR. The significant conformational changes induced by the mutation to the POR structure were analyzed by long-range molecular dynamics simulation. The results revealed that missense mutation decreased the conformational stability of POR as compared to wild type (WT). The PCA based FEL analysis described the mutant-specific conformational alterations and dominant motions essential for the biological activity of POR. The LIGPLOT interaction analysis showed the different binding architecture of FMN, FAD, and NADPH as a result of mutation. The increased number of hydrogen bonds in the FEL conformation of WT proved the strong binding of cofactors in the binding pocket as compared to the mutant. The porcupine plot analysis associated with cross-correlation analysis depicted the high-intensity flexible motion exhibited by functionally important FAD and NADPH binding domain regions. The computational findings unravel the impact of mutation at the structural level, which could be helpful in understanding the molecular mechanism of drug metabolism.

A Novel PCR-RFLP Method for Detection of POR*28 Polymorphism and its Genotype/Allele Frequencies in a Turkish Population

BACKGROUND

The Cytochrome P450 (CYP) enzymes are involved in the metabolism of many endogenous and exogenous substances. They need electrons for their activity. CYP mediated oxidation reactions require cytochrome oxidoreductase (POR) as an electron donor. A common genetic variation identified in the coding region of POR gene (POR*28) leads to an alteration in POR activity by causing amino acid change. The current study aimed to determine the allele and genotype frequencies of POR*28 in a healthy Turkish population by using a novel genotyping assay.

METHODS

A novel PCR-RFLP assay was developed for the detection of POR*28 (rs1057868) polymorphism and the obtained frequencies were compared with the data established in various ethnic groups.

RESULTS

Genotypic analysis revealed that of 209 healthy, unrelated individuals tested for POR*28 polymorphism, 55.5% of the studied subjects were homozygous for the CC genotype, 34.9% were heterozygous for the CT genotype and 9.6% were homozygous for the TT genotype. The allele frequencies were 0.73 (C) and 0.27 (T). The present results were in accordance with the Hardy- Weinberg equilibrium. The distribution of POR*28 allele varies between populations. The frequency of the T allele among members of the Turkish population was similar to frequencies in Caucasian populations but was lower than in Japanese and Chinese populations.

CONCLUSIONS

In this study, a novel method was developed, which could be applied easily in every laboratory for the genotyping of POR *28 polymorphism. The developed genotyping method and documented allele frequencies may have potential in understanding and predicting the variations in drug response/adverse reactions in pharmacotherapy and susceptibility to diseases in POR-mediated metabolism reactions.

Instability of the Human Cytochrome P450 Reductase A287P Variant Is the Major Contributor to Its Antley-Bixler Syndrome-like Phenotype

Human NADPH-cytochrome P450 oxidoreductase (POR) gene mutations are associated with severe skeletal deformities and disordered steroidogenesis. The human POR mutation A287P presents with disordered sexual development and skeletal malformations. Difficult recombinant expression and purification of this POR mutant suggested that the protein was less stable than WT. The activities of cytochrome P450 17A1, 19A1, and 21A2, critical in steroidogenesis, were similar using our purified, full-length, unmodified A287P or WT POR, as were those of several xenobiotic-metabolizing cytochromes P450, indicating that the A287P protein is functionally competent in vitro, despite its functionally deficient phenotypic behavior in vivo Differential scanning calorimetry and limited trypsinolysis studies revealed a relatively unstable A287P compared with WT protein, leading to the hypothesis that the syndrome observed in vivo results from altered POR protein stability. The crystal structures of the soluble domains of WT and A287P reveal only subtle differences between them, but these differences are consistent with the differential scanning calorimetry results as well as the differential susceptibility of A287P and WT observed with trypsinolysis. The relative in vivo stabilities of WT and A287P proteins were also examined in an osteoblast cell line by treatment with cycloheximide, a protein synthesis inhibitor, showing that the level of A287P protein post-inhibition is lower than WT and suggesting that A287P may be degraded at a higher rate. Current studies demonstrate that, unlike previously described mutations, A287P causes POR deficiency disorder due to conformational instability leading to proteolytic susceptibility in vivo, rather than through an inherent flavin-binding defect.