SLC22A5 explained

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,^[1] 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.^{[2] [3]} 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.^[4]

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.^[5] 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.^[6]

Clinical Significance

The main phenotypical effect of autosomal recessive mutations, either compound heterozygous or homozygous,^[7] 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.^{[8] [9]} 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.^[10] The symptoms and outcome of the disease can be drastically improved by replacement therapy with L-carnitine.^[11] The estimated incidence of primary carnitine deficiency in newborns is about 1 in 40,000.^[12]

Interactions

SLC22A5 interacts with PDZK1.

See also

• Solute carrier family

Further reading

• Ascunce RR, Nayar AC, Phoon CK, Srichai MB . Cardiac magnetic resonance findings in a case of carnitine deficiency . Texas Heart Institute Journal . 40 . 1 . 104–5 . 2013 . 23468586 . 3568278 .
• Erguven M, Yilmaz O, Koc S, Caki S, Ayhan Y, Donmez M, Dolunay G . A case of early diagnosed carnitine deficiency presenting with respiratory symptoms . Annals of Nutrition & Metabolism . 51 . 4 . 331–4 . 2007 . 17726310 . 10.1159/000107675 . 40574037 .
• Hwu WL, Chien YH, Tang NL, Law LK, Lin CY, Lee NC . Deficiency of the carnitine transporter (OCTN2) with partial N-acetylglutamate synthase (NAGS) deficiency . Journal of Inherited Metabolic Disease . 30 . 5 . 816 . October 2007 . 17703373 . 10.1007/s10545-007-0594-y . 2764651 .
• Makhseed N, Vallance HD, Potter M, Waters PJ, Wong LT, Lillquist Y, Pasquali M, Amat di San Filippo C, Longo N . 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 . 2004 . 15617188 . 10.1023/B:BOLI.0000045837.23328.f4 . 24144621 .
• Kinali M, Olpin SE, Clayton PT, Daubeney PE, Mercuri E, Manzur AY, Tein I, Leonard J, Muntoni F . Diagnostic difficulties in a case of primary systemic carnitine deficiency with idiopathic dilated cardiomyopathy . European Journal of Paediatric Neurology . 8 . 4 . 217–9 . 2004 . 15261886 . 10.1016/j.ejpn.2004.03.007 .
• Kinali M, Olpin SE, Clayton PT, Daubeney PE, Mercuri E, Manzur AY, Tein I, Leonard J, Muntoni F . Diagnostic difficulties in a case of primary systemic carnitine deficiency with idiopathic dilated cardiomyopathy . European Journal of Paediatric Neurology . 8 . 4 . 217–9 . 2004 . 15261886 . 10.1016/j.ejpn.2004.03.007 .
• Silverberg MS . OCTNs: will the real IBD5 gene please stand up? . World Journal of Gastroenterology . 12 . 23 . 3678–81 . June 2006 . 16773684 . 4087460 . 10.3748/wjg.v12.i23.3678 . free .
• Matsuishi T, Hirata K, Terasawa K, Kato H, Yoshino M, Ohtaki E, Hirose F, Nonaka I, Sugiyama N, Ohta K . Successful carnitine treatment in two siblings having lipid storage myopathy with hypertrophic cardiomyopathy . Neuropediatrics . 16 . 1 . 6–12 . February 1985 . 3974805 . 10.1055/s-2008-1052536 . 260240244 .
• Wu X, Prasad PD, Leibach FH, Ganapathy V . 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 . May 1998 . 9618255 . 10.1006/bbrc.1998.8669 .
• Shoji Y, Koizumi A, Kayo T, Ohata T, Takahashi T, Harada K, Takada G . 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 . July 1998 . 9634512 . 1377235 . 10.1086/301911 .
• Tamai I, Ohashi R, Nezu J, Yabuuchi H, Oku A, Shimane M, Sai Y, Tsuji A . Molecular and functional identification of sodium ion-dependent, high affinity human carnitine transporter OCTN2 . The Journal of Biological Chemistry . 273 . 32 . 20378–82 . August 1998 . 9685390 . 10.1074/jbc.273.32.20378 . free .
• 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 . Primary systemic carnitine deficiency is caused by mutations in a gene encoding sodium ion-dependent carnitine transporter . Nature Genetics . 21 . 1 . 91–4 . January 1999 . 9916797 . 10.1038/5030 . 20723174 .
• Tang NL, Ganapathy V, Wu X, Hui J, Seth P, Yuen PM, Wanders RJ, Fok TF, Hjelm NM . Mutations of OCTN2, an organic cation/carnitine transporter, lead to deficient cellular carnitine uptake in primary carnitine deficiency . Human Molecular Genetics . 8 . 4 . 655–60 . April 1999 . 10072434 . 10.1093/hmg/8.4.655 . free .
• Burwinkel B, Kreuder J, Schweitzer S, Vorgerd M, Gempel K, Gerbitz KD, Kilimann MW . Carnitine transporter OCTN2 mutations in systemic primary carnitine deficiency: a novel Arg169Gln mutation and a recurrent Arg282ter mutation associated with an unconventional splicing abnormality . Biochemical and Biophysical Research Communications . 261 . 2 . 484–7 . August 1999 . 10425211 . 10.1006/bbrc.1999.1060 .
• Wu X, Huang W, Prasad PD, Seth P, Rajan DP, Leibach FH, Chen J, Conway SJ, Ganapathy V . Functional characteristics and tissue distribution pattern of organic cation transporter 2 (OCTN2), an organic cation/carnitine transporter . The Journal of Pharmacology and Experimental Therapeutics . 290 . 3 . 1482–92 . September 1999 . 10454528 .
• Vaz FM, Scholte HR, Ruiter J, Hussaarts-Odijk LM, Pereira RR, Schweitzer S, de Klerk JB, Waterham HR, Wanders RJ . Identification of two novel mutations in OCTN2 of three patients with systemic carnitine deficiency . Human Genetics . 105 . 1–2 . 157–61 . 1999 . 10480371 . 10.1007/s004390051079 .
• Koizumi A, Nozaki J, Ohura T, Kayo T, Wada Y, Nezu J, Ohashi R, Tamai I, Shoji Y, Takada G, Kibira S, Matsuishi T, Tsuji A . Genetic epidemiology of the carnitine transporter OCTN2 gene in a Japanese population and phenotypic characterization in Japanese pedigrees with primary systemic carnitine deficiency . Human Molecular Genetics . 8 . 12 . 2247–54 . November 1999 . 10545605 . 10.1093/hmg/8.12.2247 . free .
• Seth P, Wu X, Huang W, Leibach FH, Ganapathy V . Mutations in novel organic cation transporter (OCTN2), an organic cation/carnitine transporter, with differential effects on the organic cation transport function and the carnitine transport function . The Journal of Biological Chemistry . 274 . 47 . 33388–92 . November 1999 . 10559218 . 10.1074/jbc.274.47.33388 . free .
• Mayatepek E, Nezu J, Tamai I, Oku A, Katsura M, Shimane M, Tsuji A . Two novel missense mutations of the OCTN2 gene (W283R and V446F) in a patient with primary systemic carnitine deficiency . Human Mutation . 15 . 1 . 118 . January 2000 . 10612840 . 10.1002/(SICI)1098-1004(200001)15:1<118::AID-HUMU28>3.0.CO;2-8 . free .
• Wang Y, Kelly MA, Cowan TM, Longo N . A missense mutation in the OCTN2 gene associated with residual carnitine transport activity . Human Mutation . 15 . 3 . 238–45 . 2000 . 10679939 . 10.1002/(SICI)1098-1004(200003)15:3<238::AID-HUMU4>3.0.CO;2-3 . 34117262 . free .
• Ohashi R, Tamai I, Inano A, Katsura M, Sai Y, Nezu J, Tsuji A . Studies on functional sites of organic cation/carnitine transporter OCTN2 (SLC22A5) using a Ser467Cys mutant protein . The Journal of Pharmacology and Experimental Therapeutics . 302 . 3 . 1286–94 . September 2002 . 12183691 . 10.1124/jpet.102.036004 . 1944987 .
• Rahbeeni Z, Vaz FM, Al-Hussein K, Bucknall MP, Ruiter J, Wanders RJ, Rashed MS . Identification of two novel mutations in OCTN2 from two Saudi patients with systemic carnitine deficiency . Journal of Inherited Metabolic Disease . 25 . 5 . 363–9 . September 2002 . 12408185 . 10.1023/A:1020143632011 . 25824831 .
• Elimrani I, Lahjouji K, Seidman E, Roy MJ, Mitchell GA, Qureshi I . Expression and localization of organic cation/carnitine transporter OCTN2 in Caco-2 cells . American Journal of Physiology. Gastrointestinal and Liver Physiology . 284 . 5 . G863–71 . May 2003 . 12684216 . 10.1152/ajpgi.00220.2002 .
• Karlic H, Lohninger A, Laschan C, Lapin A, Böhmer F, Huemer M, Guthann E, Rappold E, Pfeilstöcker M . Downregulation of carnitine acyltransferases and organic cation transporter OCTN2 in mononuclear cells in healthy elderly and patients with myelodysplastic syndromes . Journal of Molecular Medicine . 81 . 7 . 435–42 . July 2003 . 12802501 . 10.1007/s00109-003-0447-6 . 10992930 .
• Amat di San Filippo C, Wang Y, Longo N . Functional domains in the carnitine transporter OCTN2, defective in primary carnitine deficiency . The Journal of Biological Chemistry . 278 . 48 . 47776–84 . November 2003 . 14506273 . 10.1074/jbc.M307911200 . free .

External links

• • Primary Carnitine Deficiency (OCTN2 database)

Notes and References

1. Online Mendelian Inheritance in Man, OMIM®. Johns Hopkins University, Baltimore, MD. MIM Number: : : . World Wide Web URL: https://omim.org/
2. Zong NC, Li H, Li H, Lam MP, Jimenez RC, Kim CS, Deng N, Kim AK, Choi JH, Zelaya I, Liem D, Meyer D, Odeberg J, Fang C, Lu HJ, Xu T, Weiss J, Duan H, Uhlen M, Yates JR, Apweiler R, Ge J, Hermjakob H, Ping P . Integration of cardiac proteome biology and medicine by a specialized knowledgebase . Circulation Research . 113 . 9 . 1043–53 . October 2013 . 23965338 . 4076475 . 10.1161/CIRCRESAHA.113.301151 .
3. Web site: SLC22A5 - Solute carrier family 22 member 5 . Cardiac Organellar Protein Atlas Knowledgebase (COPaKB) . 2018-07-25 . 2018-07-26 . https://web.archive.org/web/20180726040930/https://amino.heartproteome.org/web/protein/O76082 . dead .
4. Wu X, Prasad PD, Leibach FH, Ganapathy V . 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 . May 1998 . 9618255 . 10.1006/bbrc.1998.8669 .
5. Web site: Entrez Gene: SLC22A5 solute carrier family 22 (organic cation transporter), member 5. 2018-07-25.
6. Web site: SLC22A5 - Solute carrier family 22 member 5 - Homo sapiens (Human) - SLC22A5 gene & protein. www.uniprot.org. en. 2018-07-25.
7. Lahrouchi N, Lodder EM, Mansouri M, Tadros R, Zniber L, Adadi N, Clur SB, van Spaendonck-Zwarts KY, Postma AV, Sefiani A, Ratbi I, Bezzina CR . Exome sequencing identifies primary carnitine deficiency in a family with cardiomyopathy and sudden death . European Journal of Human Genetics . 25 . 6 . 783–787 . June 2017 . 28295041 . 5477358 . 10.1038/ejhg.2017.22 .
8. Yilmaz TF, Atay M, Toprak H, Guler S, Aralasmak A, Alkan A . MRI findings in encephalopathy with primary carnitine deficiency: a case report . Journal of Neuroimaging . 25 . 2 . 325–328 . 2014-03-10 . 24612242 . 10.1111/jon.12102 . 35640542 .
9. Mazzini M, Tadros T, Siwik D, Joseph L, Bristow M, Qin F, Cohen R, Monahan K, Klein M, Colucci W . Primary carnitine deficiency and sudden death: in vivo evidence of myocardial lipid peroxidation and sulfonylation of sarcoendoplasmic reticulum calcium ATPase 2 . en . Cardiology . 120 . 1 . 52–8 . 2011 . 22116472 . 10.1159/000333127 . 207687571 .
10. Yoon YA, Lee DH, Ki CS, Lee SY, Kim JW, Lee YW, Park HD . SLC22A5 mutations in a patient with systemic primary carnitine deficiency: the first Korean case confirmed by biochemical and molecular investigation . Annals of Clinical and Laboratory Science . 42 . 4 . 424–8 . 2012 . 23090741 .
11. Agnetti A, Bitton L, Tchana B, Raymond A, Carano N . Primary carnitine deficiency dilated cardiomyopathy: 28 years follow-up . International Journal of Cardiology . 162 . 2 . e34–5 . January 2013 . 22658351 . 10.1016/j.ijcard.2012.05.038 .
12. Koizumi A, Nozaki J, Ohura T, Kayo T, Wada Y, Nezu J, Ohashi R, Tamai I, Shoji Y, Takada G, Kibira S, Matsuishi T, Tsuji A . Genetic epidemiology of the carnitine transporter OCTN2 gene in a Japanese population and phenotypic characterization in Japanese pedigrees with primary systemic carnitine deficiency . Human Molecular Genetics . 8 . 12 . 2247–54 . November 1999 . 10545605 . 10.1093/hmg/8.12.2247 . free .