Chen J, Peterson R T, Schreiber S L
Howard Hughes Medical Institute, Department of Chemistry & Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
Biochem Biophys Res Commun. 1998 Jun 29;247(3):827-32. doi: 10.1006/bbrc.1998.8792.
Protein phosphatases participate in the regulation of a variety of cellular processes. Control of their enzymatic activity and specificity is made possible largely by an array of regulatory subunits. Novel serine/threonine phosphatases--PP4 and PP6 in human cells--have been discovered recently, for which regulatory subunits are yet to be identified. We report here the identification of a potential regulatory subunit of these phosphatases. Using the yeast two-hybrid system, we have found that alpha 4, a previously identified phosphoprotein, associates constitutively with the catalytic subunits of PP4, PP6, and both isoforms of PP2A. These interactions have been confirmed by direct binding and do not require phosphorylation of alpha 4, although it is unclear whether alpha 4 phosphorylation has any effect on its association with the phosphatases. The binding activity appears to reside in the N-terminal 50 amino acids of the phosphatases, consistent with a previous observation that the first 55 residues of PPV, a Drosophila homolog of PP6, may harbor the element for regulation. alpha 4 shares 37% sequence homology with Tap42, an S. cerevisiae protein that has been reported to associate with PP2A and Sit4 (yeast homolog of PP6) and comprises a regulatory component in the rapamycin-sensitive Tor signalling pathway. By analogy, alpha 4 and its associated phosphatases may participate in the mammalian rapamycin-sensitive pathway mediated by FRAP.
蛋白质磷酸酶参与多种细胞过程的调控。它们的酶活性和特异性的控制很大程度上通过一系列调节亚基得以实现。最近发现了新型丝氨酸/苏氨酸磷酸酶——人类细胞中的PP4和PP6，但其调节亚基尚未确定。我们在此报告这些磷酸酶潜在调节亚基的鉴定。利用酵母双杂交系统，我们发现α4（一种先前鉴定的磷蛋白）持续与PP4、PP6以及PP2A的两种同工型的催化亚基结合。这些相互作用已通过直接结合得到证实，且不需要α4磷酸化，尽管尚不清楚α4磷酸化对其与磷酸酶的结合是否有任何影响。结合活性似乎存在于磷酸酶的N端50个氨基酸中，这与先前的观察结果一致，即PP6的果蝇同源物PPV的前55个残基可能含有调节元件。α4与Tap42具有37%的序列同源性，Tap42是一种酿酒酵母蛋白，据报道它与PP2A和Sit4（PP6的酵母同源物）结合，并在雷帕霉素敏感的Tor信号通路中构成一个调节成分。类推而言，α4及其相关的磷酸酶可能参与由FRAP介导的哺乳动物雷帕霉素敏感通路。
