Becker W, Kentrup H, Klumpp S, Schultz J E, Joost H G
Institut für Pharmakologie und Toxikologie, RWTH Aachen, Germany.
J Biol Chem. 1994 Sep 9;269(36):22586-92.
Two novel protein serine/threonine phosphatases were cloned from a rat fat cell library with probes generated by a polymerase chain reaction-based cloning approach. One of these cDNAs encoded a protein presumably representing the rat homologue of PPV from Drosophila (75% identity of amino acids). The other novel cDNA encoded a protein phosphatase of 499 amino acids and was designated PPT. Its catalytic domain contains motifs typical for protein phosphatases but is only distantly related with PP1, PP2A, and PP2B (38-42% identical amino acids). When expressed in Escherichia coli, the catalytic domain of PPT exhibited protein phosphatase activity (dephosphorylation of phosphorylase a) that was inhibitable by okadaic acid. As a unique feature among other members of this gene family, PPT has an amino-terminal extension of 200 amino acids harboring three tandemly arranged tetratricopeptide repeat (TPR) motifs. This domain has previously been found in other proteins involved in the regulation of RNA synthesis or mitosis. mRNA of PPT was predominantly found in brain and, in lower levels, in testis, but was nearly undetectable in spleen, lung, skeletal muscle, kidney, and liver. It is suggested that the TPR domain of PPT may be involved in the regulation of the function of this novel protein phosphatase.
利用基于聚合酶链反应的克隆方法产生的探针，从大鼠脂肪细胞文库中克隆出两种新型蛋白丝氨酸/苏氨酸磷酸酶。其中一个cDNA编码的蛋白质可能代表果蝇PPV的大鼠同源物（氨基酸序列一致性为75%）。另一个新的cDNA编码一种含有499个氨基酸的蛋白磷酸酶，命名为PPT。其催化结构域包含蛋白磷酸酶典型的基序，但与PP1、PP2A和PP2B的关系较远（氨基酸序列一致性为38 - 42%）。当在大肠杆菌中表达时，PPT的催化结构域表现出蛋白磷酸酶活性（糖原磷酸化酶a的去磷酸化），该活性可被冈田酸抑制。作为该基因家族其他成员中的独特特征，PPT有一个200个氨基酸的氨基末端延伸，其中包含三个串联排列的四肽重复（TPR）基序。该结构域先前已在其他参与RNA合成或有丝分裂调控的蛋白质中发现。PPT的mRNA主要存在于脑中，在睾丸中的水平较低，但在脾脏、肺、骨骼肌、肾脏和肝脏中几乎检测不到。提示PPT的TPR结构域可能参与这种新型蛋白磷酸酶功能的调控。
