Dorow D S, Devereux L, Tu G F, Price G, Nicholl J K, Sutherland G R, Simpson R J
Research Division, Peter MacCallum Cancer Institute, Melbourne, Victoria, Australia.
Eur J Biochem. 1995 Dec 1;234(2):492-500. doi: 10.1111/j.1432-1033.1995.492_b.x.
Protein kinases play pivotal roles in the control of many cellular processes. In a search for protein kinases expressed in human epithelial tumour cells, we discovered two members of a novel protein kinase family [Dorow, D. S., Devereux, L., Dietzsch, E. & de Kretser, T. A. (1993) Eur. J. Biochem. 213, 701-710]. Due to the unique mixture of structural domains within their amino acid sequences, we named the family mixed-lineage kinases (MLK). We initially isolated clones encoding partial cDNAs of MLK1 and 2 from a human colonic cDNA library. The MLK2 cDNA was subsequently used to screen a human brain cDNA library and we have now cloned and sequenced a 3454-bp cDNA encoding the full-length MLK2 protein. The predicted MLK2 polypeptide has 954 amino acids and contains a src homology 3 (SH3) domain, a kinase catalytic domain, a double leucine zipper and basic domain, and a large C-terminal domain. The 22-amino-acid N-terminal region has four glutamic acid residues immediately following the initiator methionine. Beginning at amino acid 23, the 55-amino-acid SH3 domain contains a 5-amino-acid insert in a position corresponding to inserts of 6 and 15 residues in the SH3 domains of n-src and the phosphatidylinositol 3'-kinase. Adjacent to the SH3 domain is a kinase catalytic domain with conserved motifs associated with both serine/threonine and tyrosine specificity. Beginning nine residues C-terminal to the catalytic domain, there are two leucine/isoleucine zippers separated by a 13-amino-acid spacer sequence and followed by a stretch of basic residues. The polybasic sequence contains a motif that is similar to nuclear localisation signals from several proteins. The C-terminal domain is composed of 491 amino acids of which 17% are serine or threonine and 16% are proline. This domain also has a biased ratio of basic to acidic amino acids with a calculated pI of 9.38. When used as a probe to examine mRNA expression in human tissues, a MLK2 cDNA hybridised to a species of 3.8 kb that was expressed at highest levels in RNA from brain and skeletal muscle. The 3454-bp cDNA was also used for fluorescence in situ hybridisation to localise the MLK2 gene to human chromosome 19 q13.2.
蛋白激酶在许多细胞过程的调控中发挥着关键作用。在对人类上皮肿瘤细胞中表达的蛋白激酶进行研究时，我们发现了一个新型蛋白激酶家族的两个成员[多罗，D.S.，德弗勒克斯，L.，迪茨施，E.和德克雷泽，T.A.（1993年）《欧洲生物化学杂志》213卷，701 - 710页]。由于其氨基酸序列中结构域的独特组合，我们将该家族命名为混合谱系激酶（MLK）。我们最初从人结肠cDNA文库中分离出编码MLK1和2部分cDNA的克隆。随后，MLK2 cDNA被用于筛选人脑cDNA文库，现在我们已经克隆并测序了一个3454 bp的cDNA，它编码全长MLK2蛋白。预测的MLK2多肽有954个氨基酸，包含一个src同源3（SH3）结构域、一个激酶催化结构域、一个双亮氨酸拉链和碱性结构域，以及一个大的C末端结构域。22个氨基酸的N末端区域在起始甲硫氨酸之后紧接着有四个谷氨酸残基。从第23个氨基酸开始，55个氨基酸的SH3结构域在对应于n-src和磷脂酰肌醇3'-激酶的SH3结构域中6个和15个残基插入的位置有一个5个氨基酸的插入。与SH3结构域相邻的是一个激酶催化结构域，具有与丝氨酸/苏氨酸和酪氨酸特异性相关的保守基序。在催化结构域的C末端九个残基处开始，有两个亮氨酸/异亮氨酸拉链，由一个13个氨基酸的间隔序列隔开，后面跟着一段碱性残基。多碱性序列包含一个与几种蛋白质的核定位信号相似的基序。C末端结构域由491个氨基酸组成，其中17%是丝氨酸或苏氨酸，16%是脯氨酸。该结构域的碱性氨基酸与酸性氨基酸的比例也有偏差，计算得到的pI为9.38。当用作探针检测人类组织中的mRNA表达时，MLK2 cDNA与一种3.8 kb的物种杂交，该物种在脑和骨骼肌的RNA中表达水平最高。这个3454 bp的cDNA也被用于荧光原位杂交，将MLK2基因定位到人类染色体19 q13.2上。
