Clinical and biochemical description of a novel CYP21A2 gene mutation 962_963insA using a new 3D model for the P450c21 protein.
OBJECTIVE
A severely virilized 46, XX newborn girl was referred to our center for evaluation and treatment of congenital adrenal hyperplasia (CAH) because of highly elevated 17alpha-hydroxyprogesterone levels at newborn screening; biochemical tests confirmed the diagnosis of salt-wasting CAH. Genetic analysis revealed that the girl was compound heterozygote for a previously reported Q318X mutation in exon 8 and a novel insertion of an adenine between nucleotides 962 and 963 in exon 4 of the CYP21A2 gene. This 962_963insA mutation created a frameshift leading to a stop codon at amino acid 161 of the P450c21 protein.


OBJECTIVE
To better understand structure-function relationships of mutant P450c21 proteins, we performed multiple sequence alignments of P450c21 with three mammalian P450s (P450 2C8, 2C9 and 2B4) with known structures as well as with human P450c17. Comparative molecular modeling of human P450c21 was then performed by MODELLER using the X-ray crystal structure of rabbit P450 2B4 as a template.


RESULTS
The new three dimensional model of human P450c21 and the sequence alignment were found to be helpful in predicting the role of various amino acids in P450c21, especially those involved in heme binding and interaction with P450 oxidoreductase, the obligate electron donor.


CONCLUSIONS
Our model will help in analyzing the genotype-phenotype relationship of P450c21 mutations which have not been tested for their functional activity in an in vitro assay.
Janner
Marco
M
Pediatric Endocrinology and Diabetology, University Children's Hospital Bern, Bern, Switzerland.
Pandey
Amit V
AV
Mullis
Primus E
PE
Flück
Christa E
CE
D000312:Adrenal Hyperplasia, Congenital / Q000235:genetics / Q000628:therapy; D000595:Amino Acid Sequence; D005091:Exons / Q000235:genetics; D005260:Female; D005838:Genotype; D006579:Heterozygote; D006801:Humans; D007231:Infant, Newborn; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000502:physiology*; D010375:Pedigree; D010641:Phenotype; D013255:Steroid 21-Hydroxylase / Q000737:chemistry* / Q000235:genetics*; D013329:Structure-Activity Relationship
D013255:Steroid 21-Hydroxylase