SLC22A5 is a membrane transport protein associated with primary carnitine deficiency. This protein is involved in the active cellular uptake of carnitine. It acts a symporter, moving sodium ions and other organic cations across the membrane along with carnitine. Such polyspecific organic cation transporters in the liver, kidney, intestine, and other organs are critical for the elimination of many endogenous small organic cations as well as a wide array of drugs and environmental toxins. Mutations in the SLC22A5 gene cause systemic primary carnitine deficiency, which can lead to heart failure.
Structure
The SLC22A5 gene, containing 10 exons, is located on the q arm of chromosome 5 in position 31.1 and spans 25,910 base pair. The gene produces a 63 kDa protein composed of 557 amino acids. The protein has 12 putative transmembrane domains, with a long extracellular loop of 107 amino acids between the first two transmembrane domains and an intracellular loop between the fourth and fifth transmembrane domains. This long extracellular loop has three potential sites for N-glycosylation, and the intracellular loop has an ATP/GTP binding motif. In putative intracellular domains, there are five potential sites for protein-kinase C-dependent phosphorylation and one for protein-kinase A-dependent phosphorylation.
Function
The SLC22A5 gene codes for a plasma integral membrane protein which functions as both an organic cation transporter and a sodium-dependent high affinity carnitine transporter. The encoded protein is involved in the active cellular uptake of carnitine, transporting one sodium ion with one molecule of carnitine. Organic cations transported by this protein include tetraethylammonium (TEA) without involvement of sodium. The relative uptake activity ratio of carnitine to TEA is 11.3.
Clinical Significance
The main phenotypical effect of autosomal recessive mutations, either compound heterozygous or homozygous, in the SLC22A5 gene is systemic primary carnitine deficiency, characterized by impaired carnitine transport, urinary carnitine wasting, low serum carnitine levels, reduced intracellular carnitine accumulation, impaired beta oxidation, and cytosolic fatty acid accumulation. Patients often display metabolic decompensation, hypoketotic hypoglycemia, hepatic encephalopathy, Reye syndrome, and sudden infant death in their first year, followed by the later onset of cardiomyopathy or skeletal myopathy, arrhythmias, muscle weakness, and heart failure in early childhood. Patients may be asymptomatic, with about 70% of asymptomatic patients having a missense mutation or in-frame deletion; nonsense mutation frequency is increased in symptomatic patients. The symptoms and outcome of the disease can be drastically improved by replacement therapy with L-carnitine. The estimated incidence of primary carnitine deficiency in newborns is about 1 in 40,000.
Interactions
See also
References
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Further reading
- Ascunce RR, Nayar AC, Phoon CK, Srichai MB (2013). "Cardiac magnetic resonance findings in a case of carnitine deficiency". Texas Heart Institute Journal. 40 (1): 104–5. PMC 3568278. PMID 23468586.
- Erguven M, Yilmaz O, Koc S, Caki S, Ayhan Y, Donmez M, Dolunay G (2007). "A case of early diagnosed carnitine deficiency presenting with respiratory symptoms". Annals of Nutrition & Metabolism. 51 (4): 331–4. doi:10.1159/000107675. PMID 17726310. S2CID 40574037.
- Hwu WL, Chien YH, Tang NL, Law LK, Lin CY, Lee NC (October 2007). "Deficiency of the carnitine transporter (OCTN2) with partial N-acetylglutamate synthase (NAGS) deficiency". Journal of Inherited Metabolic Disease. 30 (5): 816. doi:10.1007/s10545-007-0594-y. PMID 17703373. S2CID 2764651.
- Makhseed N, Vallance HD, Potter M, Waters PJ, Wong LT, Lillquist Y, Pasquali M, Amat di San Filippo C, Longo N (2004). "Carnitine transporter defect due to a novel mutation in the SLC22A5 gene presenting with peripheral neuropathy". Journal of Inherited Metabolic Disease. 27 (6): 778–80. doi:10.1023/B:BOLI.0000045837.23328.f4. PMID 15617188. S2CID 24144621.
- Kinali M, Olpin SE, Clayton PT, Daubeney PE, Mercuri E, Manzur AY, Tein I, Leonard J, Muntoni F (2004). "Diagnostic difficulties in a case of primary systemic carnitine deficiency with idiopathic dilated cardiomyopathy". European Journal of Paediatric Neurology. 8 (4): 217–9. doi:10.1016/j.ejpn.2004.03.007. PMID 15261886.
- Kinali M, Olpin SE, Clayton PT, Daubeney PE, Mercuri E, Manzur AY, Tein I, Leonard J, Muntoni F (2004). "Diagnostic difficulties in a case of primary systemic carnitine deficiency with idiopathic dilated cardiomyopathy". European Journal of Paediatric Neurology. 8 (4): 217–9. doi:10.1016/j.ejpn.2004.03.007. PMID 15261886.
- Silverberg MS (June 2006). "OCTNs: will the real IBD5 gene please stand up?". World Journal of Gastroenterology. 12 (23): 3678–81. doi:10.3748/wjg.v12.i23.3678. PMC 4087460. PMID 16773684.
- Matsuishi T, Hirata K, Terasawa K, Kato H, Yoshino M, Ohtaki E, Hirose F, Nonaka I, Sugiyama N, Ohta K (February 1985). "Successful carnitine treatment in two siblings having lipid storage myopathy with hypertrophic cardiomyopathy". Neuropediatrics. 16 (1): 6–12. doi:10.1055/s-2008-1052536. PMID 3974805. S2CID 260240244.
- Wu X, Prasad PD, Leibach FH, Ganapathy V (May 1998). "cDNA sequence, transport function, and genomic organization of human OCTN2, a new member of the organic cation transporter family". Biochemical and Biophysical Research Communications. 246 (3): 589–95. doi:10.1006/bbrc.1998.8669. PMID 9618255.
- Shoji Y, Koizumi A, Kayo T, Ohata T, Takahashi T, Harada K, Takada G (July 1998). "Evidence for linkage of human primary systemic carnitine deficiency with D5S436: a novel gene locus on chromosome 5q". American Journal of Human Genetics. 63 (1): 101–8. doi:10.1086/301911. PMC 1377235. PMID 9634512.
- Tamai I, Ohashi R, Nezu J, Yabuuchi H, Oku A, Shimane M, Sai Y, Tsuji A (August 1998). "Molecular and functional identification of sodium ion-dependent, high affinity human carnitine transporter OCTN2". The Journal of Biological Chemistry. 273 (32): 20378–82. doi:10.1074/jbc.273.32.20378. PMID 9685390.
- Nezu J, Tamai I, Oku A, Ohashi R, Yabuuchi H, Hashimoto N, Nikaido H, Sai Y, Koizumi A, Shoji Y, Takada G, Matsuishi T, Yoshino M, Kato H, Ohura T, Tsujimoto G, Hayakawa J, Shimane M, Tsuji A (January 1999). "Primary systemic carnitine deficiency is caused by mutations in a gene encoding sodium ion-dependent carnitine transporter". Nature Genetics. 21 (1): 91–4. doi:10.1038/5030. PMID 9916797. S2CID 20723174.
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- Mayatepek E, Nezu J, Tamai I, Oku A, Katsura M, Shimane M, Tsuji A (January 2000). "Two novel missense mutations of the OCTN2 gene (W283R and V446F) in a patient with primary systemic carnitine deficiency". Human Mutation. 15 (1): 118. doi:10.1002/(SICI)1098-1004(200001)15:1<118::AID-HUMU28>3.0.CO;2-8. PMID 10612840.
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External links
- SLC22A5+protein,+human at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- Primary Carnitine Deficiency (OCTN2 database)
This article incorporates text from the United States National Library of Medicine, which is in the public domain.
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see also solute carrier disorders |