Department of Immunobiology, Yale School of Medicine, PO Box 208011, New Haven, CT 06520-8011, USA.
Department of Genetics, Yale School of Medicine, PO Box 208005, New Haven, CT 06520-8005, USA.
J Mol Biol. 2019 Sep 6;431(19):3753-3770. doi: 10.1016/j.jmb.2019.07.009. Epub 2019 Jul 10.
Specific interactions between the helical membrane-spanning domains of transmembrane proteins play central roles in the proper folding and oligomerization of these proteins. However, the relationship between the hydrophobic amino acid sequences of transmembrane domains and their functional interactions is in most cases unknown. Here, we use ultra-simple artificial proteins to systematically study the sequence basis for transmembrane domain interactions. We show that most short homopolymeric polyleucine transmembrane proteins containing single amino acid substitutions can activate the platelet-derived growth factor β receptor or the erythropoietin receptor in cultured mouse cells, resulting in cell transformation or proliferation. These proteins displayed complex patterns of activity that were markedly affected by seemingly minor sequence differences in the ultra-simple protein itself or in the transmembrane domain of the target receptor, and the effects of these sequence differences are not additive. In addition, specific leucine residues along the length of these proteins are required for activity, and the positions of these required leucines differ based on the identity and position of the central substituted amino acid. Our results suggest that these ultra-simple proteins use a variety of molecular mechanisms to activate the same target and that diversification of transmembrane domain sequences over the course of evolution minimized off-target interactions.
跨膜蛋白的螺旋膜贯穿结构域之间的特定相互作用在这些蛋白质的正确折叠和寡聚化中起着核心作用。然而，在大多数情况下，跨膜结构域的疏水性氨基酸序列与其功能相互作用之间的关系尚不清楚。在这里，我们使用超简单的人工蛋白系统地研究了跨膜结构域相互作用的序列基础。我们表明，大多数含有单个氨基酸取代的短同聚多亮氨酸跨膜蛋白可以在培养的小鼠细胞中激活血小板衍生生长因子 β 受体或促红细胞生成素受体，导致细胞转化或增殖。这些蛋白表现出复杂的活性模式，这些活性模式明显受到超简单蛋白本身或靶受体跨膜结构域中看似微小的序列差异的影响，并且这些序列差异的影响不是加性的。此外，这些蛋白的长度上的特定亮氨酸残基对于活性是必需的，并且这些必需亮氨酸的位置根据中心取代氨基酸的身份和位置而不同。我们的结果表明，这些超简单的蛋白使用多种分子机制来激活相同的靶标，并且跨膜结构域序列在进化过程中的多样化最小化了非靶标相互作用。
