title: Vitamin D-Dependent Rickets Type 1 Caused by Mutations in CYP27B1 Affecting Protein Interactions With Adrenodoxin.
abstract: CYP27B1 converts 25-hydroxyvitamin D3 to active 1,25-dihydroxyvitamin D3, playing a vital role in calcium homeostasis and bone growth. Vitamin D-dependent rickets type 1 (VDDR-1) is a rare autosomal recessive disorder caused by mutations in CYP27B1.
  
  
  
  The objective of the study was an enzymatic and structural analysis of mutations in a patient with calcipenic rickets. Design, Setting, Patient, and Intervention: Two siblings presented with calcipenic rickets and normal 1,25-dihydroxyvitamin D3 levels. CYP27B1 gene analysis showed compound heterozygous mutations confirming VDDR-1. We studied wild-type CYP27B1 and mutations H441Y and R459L by computational homology modeling, molecular dynamics simulations, and functional studies using a luciferase assay. The patients were successfully treated with calcitriol.
  
  
  
  The main outcomes of the study were novel mutations leading to a severe loss of CYP27B1 activities for metabolism of 25-hydroxyvitamin D3.
  
  
  
  Mitochondrial cytochrome P450s require adrenodoxin (FDX1) and adrenodoxin reductase. We created models of CYP27B1-FDX1 complex, which revealed negative effects of mutations H441Y and R459L. Upon structural analysis, near-identical folds, protein contact areas, and orientations of heme/iron-sulfur cluster suggested that both mutations may destabilize the CYP27B1-FDX1 complex by negating directional interactions with adrenodoxin. This system is highly sensitive to small local changes modulating the binding/dissociation of adrenodoxin, and electron-transporting efficiency might change with mutations at the surface. Functional assays confirmed this hypothesis and showed severe loss of activity of CYP27B1 by both mutations.
  
  
  
  This is the first report of mutations in CYP27B1 causing VDDR-1 by affecting protein-protein interactions with FDX1 that results in reduced CYP27B1 activities. Detailed characterization of mutations in CYP27B1 is required for understanding the novel molecular mechanisms causing VDDR-1.
authors.affiliation: Division of Pediatric Endocrinology, Diabetology, and Metabolism (A.Z., B.L., C.E.F., A.V.P.), Department of Pediatrics, University Children's Hospital, Inselspital, Bern, and Department of Clinical Research, University of Bern, CH-3010 Bern, Switzerland; and Division of Endocrinology (N.S.M., N.R.), Boston Children's Hospital, and Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Adam
authors.initials: A
authors.lastname: Zalewski
authors.affiliation: Division of Pediatric Endocrinology, Diabetology, and Metabolism (A.Z., B.L., C.E.F., A.V.P.), Department of Pediatrics, University Children's Hospital, Inselspital, Bern, and Department of Clinical Research, University of Bern, CH-3010 Bern, Switzerland; and Division of Endocrinology (N.S.M., N.R.), Boston Children's Hospital, and Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Nina S
authors.initials: NS
authors.lastname: Ma
authors.affiliation: Division of Pediatric Endocrinology, Diabetology, and Metabolism (A.Z., B.L., C.E.F., A.V.P.), Department of Pediatrics, University Children's Hospital, Inselspital, Bern, and Department of Clinical Research, University of Bern, CH-3010 Bern, Switzerland; and Division of Endocrinology (N.S.M., N.R.), Boston Children's Hospital, and Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Balazs
authors.initials: B
authors.lastname: Legeza
authors.affiliation: Division of Pediatric Endocrinology, Diabetology, and Metabolism (A.Z., B.L., C.E.F., A.V.P.), Department of Pediatrics, University Children's Hospital, Inselspital, Bern, and Department of Clinical Research, University of Bern, CH-3010 Bern, Switzerland; and Division of Endocrinology (N.S.M., N.R.), Boston Children's Hospital, and Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Nora
authors.initials: N
authors.lastname: Renthal
authors.affiliation: Division of Pediatric Endocrinology, Diabetology, and Metabolism (A.Z., B.L., C.E.F., A.V.P.), Department of Pediatrics, University Children's Hospital, Inselspital, Bern, and Department of Clinical Research, University of Bern, CH-3010 Bern, Switzerland; and Division of Endocrinology (N.S.M., N.R.), Boston Children's Hospital, and Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Christa E
authors.initials: CE
authors.lastname: Flück
authors.affiliation: Division of Pediatric Endocrinology, Diabetology, and Metabolism (A.Z., B.L., C.E.F., A.V.P.), Department of Pediatrics, University Children's Hospital, Inselspital, Bern, and Department of Clinical Research, University of Bern, CH-3010 Bern, Switzerland; and Division of Endocrinology (N.S.M., N.R.), Boston Children's Hospital, and Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Amit V
authors.initials: AV
authors.lastname: Pandey
mesh_terms: D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000235:genetics* / Q000378:metabolism; D000325:Adrenodoxin / Q000378:metabolism*; D000595:Amino Acid Sequence; D015415:Biomarkers / Q000378:metabolism; D053098:Familial Hypophosphatemic Rickets / Q000235:genetics* / Q000473:pathology*; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D009154:Mutation / Q000235:genetics*; D011379:Prognosis; D017386:Sequence Homology, Amino Acid; D014807:Vitamin D / Q000031:analogs & derivatives / Q000378:metabolism; D014808:Vitamin D Deficiency / Q000150:complications
chemical_list: D015415:Biomarkers; C118756:dihydroxy-vitamin D3; D000325:Adrenodoxin; D014807:Vitamin D; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; C000600378:CYP27B1 protein, human