Brewis N D, Street A J, Prescott A R, Cohen P T
Medical Research Council Protein Phosphorylation Unit, The University, Dundee, Scotland, UK.
EMBO J. 1993 Mar;12(3):987-96. doi: 10.1002/j.1460-2075.1993.tb05739.x.
The amino acid sequence of a novel mammalian protein phosphatase, termed PPX (and designated PPP4 in the human genome nomenclature), has been deduced from the cDNA and shown to be 65% identical to PP2A alpha and PP2A beta and 45% identical to PPI isoforms, the predicted molecular mass being 35 kDa. PPX was expressed in the baculovirus system. Its substrate specificity and sensitivity to the inhibitors, okadaic acid and microcystin, were similar (but not identical) to the catalytic subunit of PP2A. However, PPX did not bind the 65 kDa regulatory subunit of PP2A. The intracellular localization of PPX was investigated by immunofluorescence using two different antibodies raised against bacterially expressed PPX and a PPX-specific peptide. These showed that although PPX was distributed throughout the cytoplasm and the nucleus, intense staining occurred at centrosomes. The centrosomal staining was apparent in interphase and at all stages of mitosis, except telophase. In contrast, antibodies directed against bacterially expressed PP2A were not specifically localized to centrosomes. The human autoantibody #5051, which stains the pericentriolar material, colocalizes with PPX antibodies, suggesting that PPX may play a role in microtubule nucleation.
一种名为PPX（在人类基因组命名法中命名为PPP4）的新型哺乳动物蛋白磷酸酶的氨基酸序列已从cDNA推导得出，结果显示它与PP2Aα和PP2Aβ的序列一致性为65%，与PPI同工型的序列一致性为45%，预测分子量为35 kDa。PPX在杆状病毒系统中表达。其底物特异性以及对抑制剂冈田酸和微囊藻毒素的敏感性与PP2A的催化亚基相似（但不完全相同）。然而，PPX不与PP2A的65 kDa调节亚基结合。使用针对细菌表达的PPX和PPX特异性肽产生的两种不同抗体，通过免疫荧光法研究了PPX在细胞内的定位。结果表明，尽管PPX分布于整个细胞质和细胞核，但在中心体处有强烈染色。中心体染色在间期以及有丝分裂的各个阶段（除末期外）均很明显。相比之下，针对细菌表达的PP2A的抗体并未特异性定位于中心体。可对中心粒周围物质进行染色的人自身抗体#5051与PPX抗体共定位，这表明PPX可能在微管成核过程中发挥作用。
