School of Life Sciences, Oxford Brookes University, Oxford OX3 0BP, United Kingdom.
J Biol Chem. 2011 Jan 28;286(4):2455-60. doi: 10.1074/jbc.M110.172403. Epub 2010 Nov 19.
The SLC36 family of transporters consists of four genes, two of which, SLC36A1 and SLC36A2, have been demonstrated to code for human proton-coupled amino acid transporters or hPATs. Here we report the characterization of the fourth member of the family, SLC36A4 or hPAT4, which when expressed in Xenopus laevis oocytes also encodes a plasma membrane amino acid transporter, but one that is not proton-coupled and has a very high substrate affinity for the amino acids proline and tryptophan. hPAT4 in Xenopus oocytes mediated sodium-independent, electroneutral uptake of [(3)H]proline, with the highest rate of uptake when the uptake medium pH was 7.4 and an affinity of 3.13 μM. Tryptophan was also an excellently transported substrate with a similarly high affinity (1.72 μM). Other amino acids that inhibited [(3)H]proline were isoleucine (K(i) 0.23 mM), glutamine (0.43 mM), methionine (0.44 mM), and alanine (1.48 mM), and with lower affinity, glycine, threonine, and cysteine (K(i) >5 mM for all). Of the amino acids directly tested for transport, only proline, tryptophan, and alanine showed significant uptake, whereas glycine and cysteine did not. Of the non-proteogenic amino acids and drugs tested, only sarcosine produced inhibition (K(i) 1.09 mM), whereas γ-aminobutyric acid (GABA), β-alanine, L-Dopa, D-serine, and δ-aminolevulinic acid were without effect on [(3)H]proline uptake. This characterization of hPAT4 as a very high affinity/low capacity non-proton-coupled amino acid transporter raises questions about its physiological role, especially as the transport characteristics of hPAT4 are very similar to the Drosophila orthologue PATH, an amino acid "transceptor" that plays a role in nutrient sensing.
SLC36 家族转运蛋白由四个基因组成，其中两个基因，SLC36A1 和 SLC36A2，已被证明编码人类质子偶联氨基酸转运体或 hPAT。在这里，我们报告了家族的第四个成员 SLC36A4 或 hPAT4 的特征，当在非洲爪蟾卵母细胞中表达时，它也编码一种质膜氨基酸转运体，但不是质子偶联的，并且对脯氨酸和色氨酸具有非常高的底物亲和力。在非洲爪蟾卵母细胞中，hPAT4 介导 [(3)H]脯氨酸的钠非依赖性、电中性摄取，当摄取介质 pH 为 7.4 时摄取速率最高，亲和力为 3.13 μM。色氨酸也是一种极好的转运底物，具有相似的高亲和力（1.72 μM）。其他抑制 [(3)H]脯氨酸摄取的氨基酸是异亮氨酸（K(i) 0.23 mM）、谷氨酰胺（0.43 mM）、蛋氨酸（0.44 mM）和丙氨酸（1.48 mM），以及亲和力较低的甘氨酸、苏氨酸和半胱氨酸（所有 K(i)>5 mM）。在直接测试的氨基酸中，只有脯氨酸、色氨酸和丙氨酸显示出明显的摄取，而甘氨酸和半胱氨酸则没有。在测试的非蛋白质氨基酸和药物中，只有肌氨酸产生抑制作用（K(i) 1.09 mM），而 γ-氨基丁酸（GABA）、β-丙氨酸、L-多巴、D-丝氨酸和 δ-氨基酮戊酸对 [(3)H]脯氨酸摄取没有影响。hPAT4 作为一种高亲和力/低容量非质子偶联氨基酸转运体的特性提出了关于其生理作用的问题，特别是因为 hPAT4 的转运特性与果蝇同源物 PATH 非常相似，PATH 是一种氨基酸“转受体”，在营养感应中发挥作用。
