Matter K, Yamamoto E M, Mellman I
Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06520-8002.
J Cell Biol. 1994 Aug;126(4):991-1004. doi: 10.1083/jcb.126.4.991.
In MDCK cells, basolateral sorting of most membrane proteins has been shown to depend on distinct cytoplasmic domain determinants. These signals can be divided into those which are related to signals for localization at clathrin-coated pits and those which are unrelated. The LDL receptor bears two tyrosine-containing signals, one of each class, that can independently target receptors from the Golgi complex and from endosomes to the basolateral plasma membrane. We have now investigated the other structural features required for the activity of both determinants. We find that both depend, at least in part, on clusters of 1-3 acidic amino acids located on the COOH-terminal side of each tyrosine. While single residues adjacent to each tyrosine were also found to be critical, the two signals differed in that only the coated pit-unrelated signal could tolerate a phenylalanine in place of its tyrosine residue. We also found that the structural requirements for basolateral targeting of the "coated pit-related" signal were distinct from those required for rapid endocytosis. Apart from sharing a common tyrosine residue, no feature of the NPXY motif for coated pit localization was required for basolateral targeting. We also investigated basolateral targeting of the mouse macrophage Fc receptor (FcRII-B2) which contains a tyrosine-independent coated pit localization signal. Basolateral transport and endocytosis were found to depend on a common dileucine-type motif. Thus, basolateral targeting determinants, like coated pit domains, can contain either tyrosine- or di-leucine-containing signals. The amino acids in the vicinity of these motifs determine whether they function as determinants for endocytosis, basolateral targeting, or both.
在MDCK细胞中，大多数膜蛋白的基底外侧分选已被证明依赖于不同的细胞质结构域决定因素。这些信号可分为与网格蛋白包被小窝定位信号相关的信号和与之无关的信号。低密度脂蛋白受体带有两类各一个含酪氨酸的信号，它们可独立地将来自高尔基体复合体和内体的受体靶向基底外侧质膜。我们现在研究了这两种决定因素发挥活性所需的其他结构特征。我们发现，两者至少部分依赖于位于每个酪氨酸COOH末端一侧的1 - 3个酸性氨基酸簇。虽然还发现每个酪氨酸相邻的单个残基也很关键，但这两个信号的不同之处在于，只有与包被小窝无关的信号能够容忍苯丙氨酸取代其酪氨酸残基。我们还发现，“与包被小窝相关”信号的基底外侧靶向的结构要求与快速内吞作用所需的结构要求不同。除了共享一个共同的酪氨酸残基外，基底外侧靶向不需要用于包被小窝定位的NPXY基序的任何特征。我们还研究了含有酪氨酸非依赖性包被小窝定位信号的小鼠巨噬细胞Fc受体（FcRII - B2）的基底外侧靶向。发现基底外侧运输和内吞作用依赖于一个共同的双亮氨酸型基序。因此，基底外侧靶向决定因素，就像包被小窝结构域一样，可以包含含酪氨酸或含双亮氨酸的信号。这些基序附近的氨基酸决定了它们是作为内吞作用、基底外侧靶向的决定因素，还是两者兼有的决定因素发挥作用。
