Volle D J, Fulton J A, Chaika O V, McDermott K, Huang H, Steinke L A, Lewis R E
Eppley Institute for Research in Cancer and Allied Diseases, Department of Biochemistry and Molecular Biology, Omaha, Nebraska 68198-6805, USA.
Biochemistry. 1999 Apr 20;38(16):5130-7. doi: 10.1021/bi983050d.
The kinase suppressor of Ras (KSR) is a loss-of-function allele that suppresses the rough eye phenotype of activated Ras in Drosophila and the multivulval phenotype of activated Ras in Caenorhabditis elegans. The physiological role of mammalian KSR is not known. We examined the mechanisms regulating the phosphorylation of this putative kinase in mammalian cells. Wild-type mouse KSR and a mutated KSR protein predicted to create a kinase-dead protein are phosphorylated identically in intact cells and in the immune complex. Phosphopeptide sequencing identified 10 in vivo phosphorylation sites in KSR, all of which reside in the 539 noncatalytic amino terminal amino acids. Expression of the amino terminal portion of KSR alone demonstrated that it was phosphorylated in the intact cell and in an immune complex in a manner indistinguishable from that of intact KSR. These data demonstrate that the kinase domain of KSR is irrelevant to its phosphorylation state and suggest that the phosphorylation of KSR and its association with a distinct set of kinases may affect intracellular signaling.
Ras激酶抑制因子（KSR）是一种功能缺失等位基因，可抑制果蝇中激活型Ras的粗糙眼表型以及秀丽隐杆线虫中激活型Ras的多阴门表型。哺乳动物KSR的生理作用尚不清楚。我们研究了哺乳动物细胞中调节这种假定激酶磷酸化的机制。野生型小鼠KSR和预测会产生激酶失活蛋白的突变KSR蛋白在完整细胞和免疫复合物中的磷酸化情况相同。磷酸肽测序确定了KSR中有10个体内磷酸化位点，所有这些位点都位于539个非催化性氨基末端氨基酸中。单独表达KSR的氨基末端部分表明，它在完整细胞和免疫复合物中的磷酸化方式与完整KSR的磷酸化方式无法区分。这些数据表明，KSR的激酶结构域与其磷酸化状态无关，并表明KSR的磷酸化及其与一组不同激酶的关联可能会影响细胞内信号传导。
