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首页> 外文期刊>American Journal of Physiology >Cytosolic COOH terminus of the peptide transporter PEPT2 is involved in apical membrane localization of the protein.
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Cytosolic COOH terminus of the peptide transporter PEPT2 is involved in apical membrane localization of the protein.

机译：肽转运蛋白PEPT2的胞质COOH末端参与蛋白质的顶膜定位。

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摘要

The peptide transporter PEPT2 is a polytopic transmembrane protein that mediates the cellular uptake of di- and tripeptides and a variety of peptidomimetics. It is widely expressed in mammalian tissues, including kidney, lung, mammary gland, choroid plexus, and glia cells. In renal tubular cells, PEPT2 is exclusively found at the apical membrane. The molecular mechanisms underlying this polarized expression and targeting to the brush-border membrane are not known. We have explored the role of the 36 COOH-terminal amino acid residues in PEPT2 trafficking and apical expression. EGFP-tagged PEPT2 wild-type transporter and various truncated and mutant proteins were expressed in the polarized proximal tubule cell lines SKPT and OK, and the cellular distribution of the fusion proteins was assessed using confocal microscopy. Whereas deletion of the last seven amino acids (delC7) did not alter PEPT2 surface expression, deletion of the next residue (delC8) or up to 30 terminal amino acids resulted in impaired apical expression and distinct accumulation of mutant proteins in endosomal and lysosomal vesicles. Truncation of more amino acids (delC36) containing tyrosine-based motifs led to a rather diffuse intracellular distribution pattern. Mutations introduced at isoleucine-720 (I720A) and leucine-722 (I722A) also caused an impaired surface appearance. Internalization assays revealed a higher endocytotic rate of the PEPT2 mutants I720A, L722A, and delC36. Our data suggest that a three-amino acid stretch (INL) and tyrosine-based motifs within the COOH tail of PEPT2 are involved in PEPT2's apical membrane localization and membrane steady-state level.
机译：肽转运蛋白PEPT2是一种多态性跨膜蛋白，可介导二肽和三肽以及多种拟肽的细胞摄取。它在哺乳动物组织中广泛表达，包括肾，肺，乳腺，脉络丛和神经胶质细胞。在肾小管细胞中，仅在顶端膜上发现了PEPT2。这种极化表达和靶向刷膜的分子机制尚不清楚。我们已经探索了36个COOH末端氨基酸残基在PEPT2转运和顶端表达中的作用。 EGFP标记的PEPT2野生型转运蛋白和各种截短和突变的蛋白在极化的近端肾小管细胞系SKPT和OK中表达，并使用共聚焦显微镜评估融合蛋白的细胞分布。删除最后七个氨基酸（delC7）不会改变PEPT2表面表达，而删除下一个残基（delC8）或最多30个末端氨基酸会导致内胚层和溶酶体囊泡中的顶基表达受损和突变蛋白的明显积累。截短更多基于酪氨酸基团的氨基酸（delC36）导致相当分散的细胞内分布模式。在异亮氨酸720（I720A）和亮氨酸722（I722A）处引入的突变也导致表面外观受损。内化分析表明，PEPT2突变体I720A，L722A和delC36具有更高的内吞率。我们的数据表明，PEPT2的COOH尾部内的三氨基酸拉伸（INL）和基于酪氨酸的基序与PEPT2的根尖膜定位和膜稳态水平有关。

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