This Article Full Text Full Text (PDF) All Versions of this Article: 93/7/2891    most recent Author Manuscript (PDF) Submit a related Letter to the Editor Purchase Article View Shopping Cart Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Google Scholar Articles by Riepe, F. G. Articles by Holterhus, P.-M. PubMed PubMed Citation Articles by Riepe, F. G. Articles by Holterhus, P.-M. Related Collections Adrenal and Hypertension Pediatric Endocrinology

Functional and Structural Consequences of a Novel Point Mutation in the CYP21A2 Gene Causing Congenital Adrenal Hyperplasia: Potential Relevance of Helix C for P450 Oxidoreductase-21-Hydroxylase Interaction

Division of Pediatric Endocrinology (F.G.R., W.G.S., P.-M.H.), Department of Pediatrics, and Biochemisches Institut (J.G.), Christian-Albrechts-Universität zu Kiel, D-24105 Kiel, Germany; Division of Pediatric Endocrinology (O.H.), Department of Pediatrics, Universität zu Lübeck, D-23560 Lübeck, Germany; and Division of Medical Sciences (N.K.), Institute of Biomedical Research, Endocrinology, and Metabolism, University of Birmingham, B4 6NN Birmingham, United Kingdom

Address all correspondence and requests for reprints to: Felix G. Riepe, M.D., Division of Pediatric Endocrinology, Department of Pediatrics, University Hospital Schleswig-Holstein, Schwanenweg 20, D-24105 Kiel, Germany. E-mail: friepe{at}pediatrics.uni-kiel.de.

Background: Congenital adrenal hyperplasia is caused by insufficient adrenal steroid biosynthesis due to impaired steroidogenic enzymes. The majority of patients suffer from deficiency of 21-hydroxylase (CYP21) coded by the CYP21A2 gene.

Objective: Our objective was to study the functional and structural consequences of the novel CYP21A2 missense mutation c.364A > C (K121Q) detected in a female patient with nonclassical 21-hydroxylase deficiency. The patient was compound heterozygous for the novel K121Q mutation and the mild P453S mutation.

Results: In vitro expression analysis of the mutant K121Q enzyme in transiently transfected COS-7 cells revealed reduced CYP21 activity of 14.0 ± 5% for the conversion of 17-hydroxyprogesterone and 19.5 ± 4% for the conversion of progesterone. K121 is located on helix C in the CYP21 protein, which is part of the heme coordinating system. In addition, helix C is involved in the interaction with the electron-providing enzyme P450 oxidoreductase. Protein modeling revealed that the substitution of glutamine for the basic amino acid lysine introduces an electrostatic change on the surface of CYP21 and may additionally change heme coordination. We hypothesize that the electron flux between P450 oxidoreductase and CYP21 is impaired and, moreover, that substrate affinity is altered due to heme dislocation with K121Q.

Conclusion: Both the interaction of P450 oxidoreductase and CYP21 as well as heme coordination are likely to be disturbed due to the K121Q mutation. Our data exemplify how the combination of in vitro expression and structural protein analysis provide novel insights into molecular mechanisms of reduced CYP21 activity, eventually explaining the patient’s phenotype.