Charbonneau H, Tonks N K, Walsh K A, Fischer E H
Department of Biochemistry, University of Washington, Seattle 98195.
Proc Natl Acad Sci U S A. 1988 Oct;85(19):7182-6. doi: 10.1073/pnas.85.19.7182.
A major protein tyrosine phosphatase (PTPase 1B) has been isolated in essentially homogeneous form from the soluble and particulate fractions of human placenta. Unexpectedly, partial amino acid sequences displayed no homology with the primary structures of the protein Ser/Thr phosphatases deduced from cDNA clones. However, the sequence is strikingly similar to the tandem C-terminal homologous domains of the leukocyte common antigen (CD45). A 157-residue segment of PTPase 1B displayed 40% and 33% sequence identity with corresponding regions from cytoplasmic domains I and II of human CD45. Similar degrees of identity have been observed among the catalytic domains of families of regulatory proteins such as protein kinases and cyclic nucleotide phosphodiesterases. On this basis, it is proposed that the CD45 family has protein tyrosine phosphatase activity and may represent a set of cell-surface receptors involved in signal transduction. This suggests that the repertoire of signal transduction mechanisms may include the direct control of an intracellular protein tyrosine phosphatase, offering the possibility of a regulatory balance with those protein tyrosine kinases that act at the internal surface of the membrane.
一种主要的蛋白质酪氨酸磷酸酶（PTPase 1B）已从人胎盘的可溶性和颗粒性组分中以基本纯的形式分离出来。出乎意料的是，部分氨基酸序列与从cDNA克隆推导的蛋白质丝氨酸/苏氨酸磷酸酶的一级结构没有同源性。然而，该序列与白细胞共同抗原（CD45）的串联C端同源结构域惊人地相似。PTPase 1B的一个157个残基的片段与人类CD45胞质结构域I和II的相应区域显示出40%和33%的序列同一性。在诸如蛋白激酶和环核苷酸磷酸二酯酶等调节蛋白家族的催化结构域之间也观察到了相似程度的同一性。在此基础上，有人提出CD45家族具有蛋白质酪氨酸磷酸酶活性，可能代表一组参与信号转导的细胞表面受体。这表明信号转导机制可能包括对细胞内蛋白质酪氨酸磷酸酶的直接控制，从而有可能与作用于膜内表面的那些蛋白质酪氨酸激酶实现调节平衡。
