Hilton D J, Watowich S S, Katz L, Lodish H F
Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142, USA.
J Biol Chem. 1996 Mar 1;271(9):4699-708. doi: 10.1074/jbc.271.9.4699.
The WSXWS motif in the extracellular domain defines members of the cytokine receptor family, yet its role in receptor structure and function remains unresolved. To address this question we have generated a panel of 100 mutants within the WSXWS motif of the erythropoietin receptor, which represents all single amino acid substitutions of these five amino acids. All mutants were synthesized at the same level; however, their passage from the endoplasmic reticulum to the Golgi apparatus differed. Because of this, expression of mutant receptors at the cell surface varied more than 300-fold. The tolerance of the tryptophan and serine residues to substitution was quite narrow; as a result, most of these mutants were retained in the endoplasmic reticulum and showed no cell surface expression or reduced cell surface expression. Although many mutants with substitutions at the middle residue of the motif reached the cell surface, it was notable that one mutant, A234E, was processed more efficiently than the wild type receptor and was expressed in elevated numbers at the cell surface. Despite this variation, all mutant receptors that reached the cell surface appeared able to bind erythropoietin and transduce a proliferative signal normally. These results are discussed in terms of a general model for WSXWS function in which the motif contributes to efficient receptor folding.
胞外域中的WSXWS基序定义了细胞因子受体家族的成员，但其在受体结构和功能中的作用仍未明确。为了解决这个问题，我们在促红细胞生成素受体的WSXWS基序内构建了一组100个突变体，它们代表了这五个氨基酸的所有单氨基酸替换。所有突变体的合成水平相同；然而，它们从内质网到高尔基体的转运情况有所不同。因此，突变受体在细胞表面的表达差异超过300倍。色氨酸和丝氨酸残基对替换的耐受性相当狭窄；结果，这些突变体中的大多数被滞留在内质网中，没有细胞表面表达或细胞表面表达减少。尽管许多在基序中间残基处有替换的突变体到达了细胞表面，但值得注意的是，一个突变体A234E比野生型受体的加工效率更高，在细胞表面的表达量也有所增加。尽管存在这种差异，但所有到达细胞表面的突变受体似乎都能够正常结合促红细胞生成素并转导增殖信号。我们根据WSXWS功能的一般模型对这些结果进行了讨论，在该模型中，基序有助于受体的有效折叠。
