Potts M, Sun H, Mockaitis K, Kennelly P J, Reed D, Tonks N K
Department of Biochemistry and Nutrition, Virginia Polytechnic Institute and State University, Blacksburg 24061-0308.
J Biol Chem. 1993 Apr 15;268(11):7632-5.
Protein-tyrosine phosphorylation has long been regarded as an exclusively eukaryotic phenomenon. Although some non-eukaryotes, mainly viruses, possess genes encoding protein-tyrosine kinases or protein-tyrosine phosphatases, these were probably appropriated from the eukaryotic hosts that constitute the sites of action of these enzymes. Herein we identify a gene, iphP, from the chromosome of the cyanobacterium Nostoc commune UTEX 584 that contains the His-Cys-Xaa-Ala-Gly-Xaa-Xaa-Arg sequence characteristic of known protein-tyrosine phosphatases. The expressed gene product, IphP, displayed protein-tyrosine phosphatase activity toward phosphotyrosine residues on reduced, carboxyamidomethylated, and maleylated lysozyme with optimum activity at pH 5.0. In addition, IphP dephosphorylated the phosphoseryl groups on casein that had been phosphorylated by the cAMP-dependent protein kinase. Cell lysates of N. commune probed with antibodies to phosphotyrosine indicated the presence of a tyrosine-phosphorylated protein of M(r) approximately 85 kDa. This tyrosine-phosphorylated protein was detected in cells grown in the presence of combined nitrogen but not in nitrogen-deficient media that induces the formation of differentiated N2-fixing cells (heterocysts). Together, these data suggest a role for protein-tyrosine phosphorylation in regulating cellular functions in this cyanobacterium. IphP is the first protein-tyrosine phosphatase to be discovered that is encoded by the chromosomal DNA of any prokaryote. Given the free-living nature of N. commune and the phylogenetic antiquity of the cyanobacteria, these findings suggest for the first time the existence of a protein-tyrosine phosphatase of genuine, unambiguous prokaryotic ancestry, thus raising fundamental questions as to the origin and role of tyrosine phosphorylation.
蛋白质酪氨酸磷酸化长期以来一直被视为真核生物独有的现象。尽管一些非真核生物，主要是病毒，拥有编码蛋白质酪氨酸激酶或蛋白质酪氨酸磷酸酶的基因，但这些基因可能是从构成这些酶作用位点的真核宿主那里获得的。在此，我们从蓝细菌集胞藻Nostoc commune UTEX 584的染色体中鉴定出一个基因iphP，它含有已知蛋白质酪氨酸磷酸酶特有的His-Cys-Xaa-Ala-Gly-Xaa-Xaa-Arg序列。表达的基因产物IphP对还原型、羧酰胺甲基化型和马来酰化型溶菌酶上的磷酸酪氨酸残基表现出蛋白质酪氨酸磷酸酶活性，在pH 5.0时活性最佳。此外，IphP使被cAMP依赖性蛋白激酶磷酸化的酪蛋白上的磷酸丝氨酸基团去磷酸化。用抗磷酸酪氨酸抗体检测集胞藻的细胞裂解物，结果表明存在一种分子量约为85 kDa的酪氨酸磷酸化蛋白。在结合氮存在的情况下生长的细胞中检测到了这种酪氨酸磷酸化蛋白，但在诱导形成分化的固氮细胞（异形胞）的缺氮培养基中未检测到。这些数据共同表明蛋白质酪氨酸磷酸化在调节这种蓝细菌的细胞功能中发挥作用。IphP是第一个被发现由任何原核生物的染色体DNA编码的蛋白质酪氨酸磷酸酶。鉴于集胞藻的自由生活性质以及蓝细菌的系统发育古老性，这些发现首次表明存在一种真正的、明确源自原核生物的蛋白质酪氨酸磷酸酶，从而引发了关于酪氨酸磷酸化的起源和作用的基本问题。
