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通过TAT1对芳香族氨基酸的再循环使得中性氨基酸能够通过LAT2-4F2hc交换体流出。

Recycling of aromatic amino acids via TAT1 allows efflux of neutral amino acids via LAT2-4F2hc exchanger.

作者信息

Ramadan Tamara, Camargo Simone M R, Herzog Brigitte, Bordin Mauro, Pos Klaas M, Verrey Francois

机构信息

Zurich Centre for Integrative Human Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.

出版信息

Pflugers Arch. 2007 Jun;454(3):507-16. doi: 10.1007/s00424-007-0209-3. Epub 2007 Feb 2.

Abstract

The rate of amino acid efflux from individual cells needs to be adapted to cellular demands and plays a central role for the control of extracellular amino acid homeostasis. A particular example of such an outward amino acid transport is the basolateral efflux from transporting epithelial cells located in the small intestine and kidney proximal tubule. Because LAT2-4F2hc (Slc7a8-Slc3a2), the best known basolateral neutral amino acid transporter of these epithelial cells, functions as an obligatory exchanger, we tested whether TAT1 (Slc16a10), the aromatic amino-acid facilitated diffusion transporter, might allow amino acid efflux via this exchanger by recycling its influx substrates. In this study, we show by immunofluorescence that TAT1 and LAT2 indeed colocalize in the early kidney proximal tubule. Using the Xenopus laevis oocytes expression system, we show that L-glutamine is released from oocytes into an amino-acid-free medium only when both transporters are coexpressed. High-performance liquid chromatography analysis reveals that several other neutral amino acids are released as well. The transport function of both TAT1 and LAT2-4F2hc is necessary for this efflux, as coexpression of functionally inactive but surface-expressed mutants is ineffective. Based on negative results of coimmunoprecipitation and crosslinking experiments, the physical interaction of these transporters does not appear to be required. Furthermore, replacement of TAT1 or LAT2-4F2hc by the facilitated diffusion transporter LAT4 or the obligatory exchanger LAT1, respectively, supports similar functional cooperation. Taken together, the results suggest that the aromatic amino acid diffusion pathway TAT1 can control neutral amino acid efflux via neighboring exchanger LAT2-4F2hc, by recycling its aromatic influx substrates.

摘要

单个细胞的氨基酸流出速率需要根据细胞需求进行调整,并且在控制细胞外氨基酸稳态中起着核心作用。这种向外的氨基酸转运的一个具体例子是位于小肠和近端肾小管的转运上皮细胞的基底外侧流出。由于这些上皮细胞中最著名的基底外侧中性氨基酸转运体LAT2 - 4F2hc(Slc7a8 - Slc3a2)作为一种强制性交换体发挥作用,我们测试了芳香族氨基酸易化扩散转运体TAT1(Slc16a10)是否可能通过循环其流入底物,经由这种交换体实现氨基酸流出。在本研究中,我们通过免疫荧光显示TAT1和LAT2确实在早期近端肾小管中共定位。使用非洲爪蟾卵母细胞表达系统,我们发现只有当这两种转运体共表达时,L - 谷氨酰胺才会从卵母细胞释放到无氨基酸培养基中。高效液相色谱分析表明,其他几种中性氨基酸也会被释放。TAT1和LAT2 - 4F2hc的转运功能对于这种流出是必需的,因为共表达功能失活但表面表达的突变体是无效的。基于免疫共沉淀和交联实验的阴性结果,这些转运体之间似乎不需要物理相互作用。此外,分别用易化扩散转运体LAT4或强制性交换体LAT1替代TAT1或LAT2 - 4F2hc,也支持类似的功能协作。综上所述,结果表明芳香族氨基酸扩散途径TAT1可以通过循环其芳香族流入底物,经由相邻的交换体LAT2 - 4F2hc控制中性氨基酸流出。

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