Sadowski I, Stone J C, Pawson T
Mol Cell Biol. 1986 Dec;6(12):4396-408. doi: 10.1128/mcb.6.12.4396-4408.1986.
Proteins encoded by oncogenes such as v-fps/fes, v-src, v-yes, v-abl, and v-fgr are cytoplasmic protein tyrosine kinases which, unlike transmembrane receptors, are localized to the inside of the cell. These proteins possess two contiguous regions of sequence identity: a C-terminal catalytic domain of 260 residues with homology to other tyrosine-specific and serine-threonine-specific protein kinases, and a unique domain of approximately 100 residues which is located N terminal to the kinase region and is absent from kinases that span the plasma membrane. In-frame linker insertion mutations in Fujinami avian sarcoma virus which introduced dipeptide insertions into the most stringently conserved segment of this N-terminal domain in P130gag-fps impaired the ability of Fujinami avian sarcoma virus to transform rat-2 cells. The P130gag-fps proteins encoded by these transformation-defective mutants were deficient in protein-tyrosine kinase activity in rat cells. However v-fps polypeptides derived from the mutant Fujinami avian sarcoma virus genomes and expressed in Escherichia coli as trpE-v-fps fusion proteins displayed essentially wild-type enzymatic activity, even though they contained the mutated sites. Deletion of the N-terminal domain from wild-type and mutant v-fps bacterial proteins had little effect on autophosphorylating activity. The conserved N-terminal domain of P130gag-fps is therefore not required for catalytic activity, but can profoundly influence the adjacent kinase region. The presence of this noncatalytic domain in all known cytoplasmic tyrosine kinases of higher and lower eucaryotes argues for an important biological function. The relative inactivity of the mutant proteins in rat-2 cells compared with bacteria suggests that the noncatalytic domain may direct specific interactions of the enzymatic region with cellular components that regulate or mediate tyrosine kinase function.
由致癌基因如v-fps/fes、v-src、v-yes、v-abl和v-fgr编码的蛋白质是细胞质蛋白酪氨酸激酶，与跨膜受体不同，它们定位于细胞内部。这些蛋白质具有两个连续的序列同源区域：一个由260个残基组成的C末端催化结构域，与其他酪氨酸特异性和丝氨酸-苏氨酸特异性蛋白激酶具有同源性；以及一个独特的结构域，约100个残基，位于激酶区域的N末端，而跨质膜的激酶中不存在该结构域。在 Fujinami 禽肉瘤病毒中发生的框内接头插入突变，将二肽插入到P130gag-fps中该N末端结构域最严格保守的片段，损害了 Fujinami 禽肉瘤病毒转化大鼠-2细胞的能力。这些转化缺陷型突变体编码的P130gag-fps蛋白在大鼠细胞中缺乏蛋白酪氨酸激酶活性。然而，源自突变的 Fujinami 禽肉瘤病毒基因组并在大肠杆菌中作为trpE-v-fps融合蛋白表达的v-fps多肽，即使它们含有突变位点，也表现出基本的野生型酶活性。从野生型和突变型v-fps细菌蛋白中缺失N末端结构域对自身磷酸化活性影响不大。因此，P130gag-fps保守的N末端结构域对于催化活性不是必需的，但可以深刻影响相邻的激酶区域。在所有已知的高等和低等真核生物的细胞质酪氨酸激酶中都存在这个非催化结构域，这表明它具有重要的生物学功能。与细菌相比，突变蛋白在大鼠-2细胞中的相对无活性表明，非催化结构域可能指导酶区域与调节或介导酪氨酸激酶功能的细胞成分的特异性相互作用。
