Sodium/potassium/calcium exchanger 5 (NCKX5), also known as solute carrier family 24 member 5 (SLC24A5), is a protein that in humans is encoded by the SLC24A5gene that has a major influence on natural skin colour variation.[1] The NCKX5 protein is a member of the potassium-dependent sodium/calcium exchanger family. Sequence variation in the SLC24A5 gene, particularly a non-synonymous SNP changing the amino acid at position 111 in NCKX5 from alanine to threonine, has been associated with differences in skin pigmentation.[2]
The SLC24A5 gene's derived threonine or Ala111Thr allele (rs1426654[3]) has been shown to be a major factor in the light skin tone of Europeans compared to Sub-SaharanAfricans, and is believed to represent as much as 25–40% of the average skin tone difference between Europeans and West Africans.[1][4] It has been the subject of recent selection in Europe, and is fixed in European populations.[5][6][7]
The SLC24A5 gene, in humans, is located on the long (q) arm of chromosome 15 on position 21.1, from base pair 46,200,461 to base pair 46,221,881.[1]
Protein
NCKX5 is 43 kDa protein that is partially localized to the trans-Golgi network in melanocytes. Removal of the NCKX5 protein disrupts melanogenesis in human and mouse melanocytes, causing a significant reduction in melanin pigment production. Site-directed mutagenesis corresponding to a non-synonymous single nucleotide polymorphism in SLC24A5 alters a residue in NCKX5 (A111T) that is important for NCKX5 sodium-calcium exchanger activity.[2]
SLC24A5 appears to have played a key role in the evolution of light skin in humans of European ancestry. The gene's function in pigmentation was discovered in zebrafish as a result of the positional cloning of the gene responsible for the "golden" variety of this common pet store fish. Evidence in the International HapMap Project database of genetic variation in human populations showed that Europeans, represented by the "CEU" population, had two primary alleles differing by only one nucleotide, changing the 111th amino acid from alanine to threonine, abbreviated "A111T".[1][8][9]
The derived threonine allele (Ala111Thr; also known as A111T or Thr111) represented 98.7 to 100% of the alleles in European samples, while the ancestral or alanine form was found in 93 to 100% of samples of Sub-Saharan Africans, East Asians and Indigenous Americans. The variation is a SNP polymorphism rs1426654, which had been previously shown to be second among 3011 tabulated SNPs ranked as ancestry-informative markers. This single change in SLC24A5 explains between 25 and 38% of the difference in skin melanin index between peoples of sub-Saharan African and European ancestry.[1]
The SNP rs2470102 independently affect skin pigmentation variation among the South Asian population.[10]
Furthermore, the European mutation is associated with the largest region of diminished genetic variation in the CEU HapMap population, suggesting the possibility that the A111T mutation may be the subject of the single largest degree of selection in human populations of European ancestry.[1] It is theorised that selection for the derived allele is based on the need for sunlight to produce the essential nutrient vitamin D. In northerly latitudes, where there is less sun, greater requirement for body coverage due to colder climate, and frequently, diets poor in vitamin D, making lighter skin more suitable for survival.[11] Tests for this variation have obvious application to forensic science.
The earliest known sample of the threonine allele is 13,000 years old from Satsurblia Cave in Georgia.[12] The allele was widespread from Anatolia to Iran at the beginning of the Neolithic, and was introduced to Europe with the arrival of the first farmers from this region about 8,000 years ago.[13][14]
↑ 1.01.11.21.31.41.5Lamason RL, Mohideen MA, Mest JR, Wong AC, Norton HL, Aros MC, Jurynec MJ, Mao X, Humphreville VR, Humbert JE, Sinha S, Moore JL, Jagadeeswaran P, Zhao W, Ning G, Makalowska I, McKeigue PM, O'donnell D, Kittles R, Parra EJ, Mangini NJ, Grunwald DJ, Shriver MD, Canfield VA, Cheng KC (December 2005). "SLC24A5, a putative cation exchanger, affects pigmentation in zebrafish and humans". Science. 310 (5755): 1782–6. doi:10.1126/science.1116238. PMID16357253.
↑ 2.02.1Ginger RS, Askew SE, Ogborne RM, Wilson S, Ferdinando D, Dadd T, Smith AM, Kazi S, Szerencsei RT, Winkfein RJ, Schnetkamp PP, Green MR (February 2008). "SLC24A5 encodes a trans-Golgi network protein with potassium-dependent sodium-calcium exchange activity that regulates human epidermal melanogenesis". The Journal of Biological Chemistry. 283 (9): 5486–95. doi:10.1074/jbc.M707521200. PMID18166528.
↑Norton HL, Kittles RA, Parra E, McKeigue P, Mao X, Cheng K, Canfield VA, Bradley DG, McEvoy B, Shriver MD (March 2007). "Genetic evidence for the convergent evolution of light skin in Europeans and East Asians". Molecular Biology and Evolution. 24 (3): 710–22. doi:10.1093/molbev/msl203. PMID17182896. Lay summary – Science Magazine.
↑Soejima M, Koda Y (January 2007). "Population differences of two coding SNPs in pigmentation-related genes SLC24A5 and SLC45A2". International Journal of Legal Medicine. 121 (1): 36–9. doi:10.1007/s00414-006-0112-z. PMID16847698.
↑Jones ER, Gonzalez-Fortes G, Connell S, Siska V, Eriksson A, Martiniano R, McLaughlin RL, Gallego Llorente M, Cassidy LM, Gamba C, Meshveliani T, Bar-Yosef O, Müller W, Belfer-Cohen A, Matskevich Z, Jakeli N, Higham TF, Currat M, Lordkipanidze D, Hofreiter M, Manica A, Pinhasi R, Bradley DG (November 2015). "Upper Palaeolithic genomes reveal deep roots of modern Eurasians". Nature Communications. 6: 8912. doi:10.1038/ncomms9912. PMC4660371. PMID26567969.
↑Broushaki F, Thomas MG, Link V, López S, van Dorp L, Kirsanow K, Hofmanová Z, Diekmann Y, Cassidy LM, Díez-del-Molino D, Kousathanas A, Sell C, Robson HK, Martiniano R, Blöcher J, Scheu A, Kreutzer S, Bollongino R, Bobo D, Davoudi H, Munoz O, Currat M, Abdi K, Biglari F, Craig OE, Bradley DG, Shennan S, Veeramah KR, Mashkour M, Wegmann D, Hellenthal G, Burger J (July 2016). "Early Neolithic genomes from the eastern Fertile Crescent". Science. 353 (6298): 499–503. doi:10.1126/science.aaf7943. PMC5113750. PMID27417496.
↑Mathieson, Iain; Lazaridis, Iosif; Rohland, Nadin; Mallick, Swapan; Patterson, Nick; Roodenberg, Songul Alpaslan; Harney, Eadaoin; Stewardson, Kristin; Fernandes, Daniel (2015-10-10). "Eight thousand years of natural selection in Europe". bioRxiv016477.
Further reading
Grønskov K, Ek J, Sand A, Scheller R, Bygum A, Brixen K, Brondum-Nielsen K, Rosenberg T (March 2009). "Birth prevalence and mutation spectrum in danish patients with autosomal recessive albinism". Investigative Ophthalmology & Visual Science. 50 (3): 1058–64. doi:10.1167/iovs.08-2639. PMID19060277.
Cook AL, Chen W, Thurber AE, Smit DJ, Smith AG, Bladen TG, Brown DL, Duffy DL, Pastorino L, Bianchi-Scarra G, Leonard JH, Stow JL, Sturm RA (February 2009). "Analysis of cultured human melanocytes based on polymorphisms within the SLC45A2/MATP, SLC24A5/NCKX5, and OCA2/P loci". The Journal of Investigative Dermatology. 129 (2): 392–405. doi:10.1038/jid.2008.211. PMID18650849.
Sulem P, Gudbjartsson DF, Stacey SN, Helgason A, Rafnar T, Magnusson KP, Manolescu A, Karason A, Palsson A, Thorleifsson G, Jakobsdottir M, Steinberg S, Pálsson S, Jonasson F, Sigurgeirsson B, Thorisdottir K, Ragnarsson R, Benediktsdottir KR, Aben KK, Kiemeney LA, Olafsson JH, Gulcher J, Kong A, Thorsteinsdottir U, Stefansson K (December 2007). "Genetic determinants of hair, eye and skin pigmentation in Europeans". Nature Genetics. 39 (12): 1443–52. doi:10.1038/ng.2007.13. PMID17952075.
Cai X, Lytton J (February 2004). "Molecular cloning of a sixth member of the K+-dependent Na+/Ca2+ exchanger gene family, NCKX6". The Journal of Biological Chemistry. 279 (7): 5867–76. doi:10.1074/jbc.M310908200. PMID14625281.
Chi A, Valencia JC, Hu ZZ, Watabe H, Yamaguchi H, Mangini NJ, Huang H, Canfield VA, Cheng KC, Yang F, Abe R, Yamagishi S, Shabanowitz J, Hearing VJ, Wu C, Appella E, Hunt DF (November 2006). "Proteomic and bioinformatic characterization of the biogenesis and function of melanosomes". Journal of Proteome Research. 5 (11): 3135–44. doi:10.1021/pr060363j. PMID17081065.
Soejima M, Koda Y (January 2007). "Population differences of two coding SNPs in pigmentation-related genes SLC24A5 and SLC45A2". International Journal of Legal Medicine. 121 (1): 36–9. doi:10.1007/s00414-006-0112-z. PMID16847698.
Dimisianos G, Stefanaki I, Nicolaou V, Sypsa V, Antoniou C, Poulou M, Papadopoulos O, Gogas H, Kanavakis E, Nicolaidou E, Katsambas AD, Stratigos AJ (February 2009). "A study of a single variant allele (rs1426654) of the pigmentation-related gene SLC24A5 in Greek subjects". Experimental Dermatology. 18 (2): 175–7. doi:10.1111/j.1600-0625.2008.00758.x. PMID18637132.
