Fine-mapping, mutation analyses, and structural mapping of cerebrotendinous xanthomatosis in U.S. pedigrees
| Autor: | Gerald Salen, Mi-Hye Lee, John D. Carpten, Sonia Yi, Glenn T. Gerhardt, Jonathan Cohen, Starr Hazard, Shailendra B. Patel |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2001 |
| Předmět: |
Adult
Male Models Molecular Adolescent Genotype Genetic Linkage Protein Conformation Molecular Sequence Data QD415-436 Biology medicine.disease_cause Biochemistry Article Adrenodoxin reductase Frameshift mutation Exon Endocrinology Cytochrome P-450 Enzyme System medicine Prevalence Missense mutation Humans genetics Amino Acid Sequence Gene Chromosomes Artificial Yeast Aged DNA Primers bile acids Genetics Mutation Base Sequence Sequence Homology Amino Acid cholesterol Cell Biology Exons Xanthomatosis Cerebrotendinous Middle Aged Molecular biology cholestanol Sterol Stop codon United States Pedigree Steroid Hydroxylases Cholestanetriol 26-Monooxygenase Female |
| Zdroj: | Journal of Lipid Research, Vol 42, Iss 2, Pp 159-169 (2001) |
| Popis: | The conversion of cholesterol into bile acids by the liver represents the major mechanism for the removal of cholesterol from the body (1). In the biosynthesis of bile acids, involving microsomal, mitochondrial, and peroxisomal compartments, enzymes modify both the ring structure and the side chain of cholesterol by oxidation, resulting in the formation of the primary bile acids, cholic acid and chenodeoxycholic acid (1). Sterol 27-hydroxylase (EC 1.14.13.15) is a member of the mitochondrial cytochrome P450 family catalyzing the initial oxidation of the side chain of sterol intermediates in hepatic bile acid synthesis (2, 3). Together with two protein cofactors, adrenodoxin and adrenodoxin reductase, sterol 27-hydroxylase hydroxylates a variety of sterol substrates at the C-27 position, and in addition can hydroxylate vitamin D3 in the C-1 and C-25 positions (3). Cerebrotendinous xanthomatosis (CTX) is a rare inherited sterol storage disorder caused by a deficiency of sterol 27-hydroxylase (4). CTX is characterized by abnormal deposition of cholesterol and cholestanol in body tissues (5, 6). Clinical progression of the disease is variable. Some patients develop severe symptoms early in infancy (7–10), whereas others first present clinical symptoms in middle age (4). In general, characteristic clinical features of CTX are the presence of juvenile cataracts and tendon xanthomas (4). Progressive neurological dysfunction may be present, if diagnosis has not been made early in life. The latter includes behavioral abnormalities; dementia; pyramidal paresis; cerebellar, brainstem, spinal, and peripheral nerve disorders; and epileptic seizures (4, 11). In addition, osteoporosis with frequent bone fractures and premature atherosclerosis have been documented (4). The isolation and characterization of the sterol 27-hydroxylase gene (CYP27) allows for the early detection of CTX patients and the identification of healthy carriers at the molecular level (12–14). CYP27 has been mapped to the distal portion (q33-qter) of the long arms of chromosome 2, although its fine map has not been reported (13). Sterol 27-hydroxylase, encoded by nine exons, consists of a 33-amino acid mitochondrial signal sequence (12), followed by a mature protein of 498 amino acids (14). It is a member of a large mitochondrial cytochrome P450 family (15) containing an adrenodoxin-binding site (residues 351–365) and the heme-binding site (residues 435–464) (12, 14, 16). About 37 different mutations of the CYP27 gene have been identified in CTX patients drawn from various populations (13, 14, 17–39). A large majority of these affect splice sites and are predicted to affect message stability or lead to abnormal splicing. Others lead to a nonsense stop codon and premature translational stop. Mutations that disrupt splicing often lead to rapid degradation of the aberrant mRNA, or lead to frame shift and translation of a polypeptide that would be predicted to be enzymatically inactive, because the heme or adrenodoxin domains are absent. All of these are therefore “null mutations.” Only 16 mutations are missense mutations that could lead to expression of the CYP27 protein. Of these, 10 are predicted to disrupt either the heme-binding or the adrenodoxin-binding domain, as they map within the identified binding sites (29). The other missense mutations are apparently located outside these domains and their functional effects have yet to be determined. It is possible that similarly occurring mutations might provide insights into the active center and/or the tertiary structure of sterol 27-hydroxylase. In the present study, we have assembled 12 previously unreported pedigrees, and one other proband, from the United States that were clinically diagnosed with CTX. We initially fine mapped CYP27 to a yeast artificial chromosome (YAC) contig and used a set of flanking microsatellite markers to genotype all the CTX families. On the basis of the haplotype and linkage analysis, no evidence of genetic heterogeneity was found. Recombination analyses allowed us to refine the mapping data. Mutations of the sterol 27-hydroxylase gene from the 13 CTX probands were identified. All probands, except two, were heterozygous for mutations. Twenty-three mutations in total were identified, five of which are novel. Using structural modeling, we have mapped all the known missense mutations onto a putative three-dimensional model of sterol 27-hydroxylase. Most of the missense mutations appear to disrupt the heme- or adrenodoxin-binding sites, on the basis of their location in these domains. However, two missense mutations map well outside these areas and thus may be important in either substrate entry into the active site, or in an unidentified biological function that is critical for enzyme activity. |
| Databáze: | OpenAIRE |
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