Bennett D, Szöor B, Alphey L
Department of Zoology, University of Oxford, U.K.
Biochemistry. 1999 Dec 7;38(49):16276-82. doi: 10.1021/bi9917028.
Phosphatase inhibitor-2 (I-2) is a mammalian phosphoprotein that binds to the catalytic subunit of type 1 serine/threonine phosphoprotein phosphatase (PP1c) and inhibits its activity in vitro. Recombinant PP1c differs from native PP1c in several biochemical criteria, including the requirement for Mn(2+), sensitivity to vanadate, and p-nitrophenyl phosphate (pNPP) phosphatase activity. I-2 can convert recombinant PP1c into a native-like activity in vitro. It has therefore been suggested that I-2 may act as a molecular chaperone for PP1 in vivo. We have identified a Drosophila homologue (I-2Dm) in a two-hybrid screen for PP1c-binding proteins. The sequence of I-2Dm is 35% identical with that of I-2, whereas the catalytic subunits themselves are >85% identical in flies and humans; however, we show that many biochemical properties of I-2 are conserved. Like I-2, I-2Dm can convert recombinant PP1c to a native-like activity. This strongly suggests that this ability is an essential, conserved role of I-2 and I-2Dm.
磷酸酶抑制剂-2（I-2）是一种哺乳动物磷蛋白，它能与1型丝氨酸/苏氨酸磷蛋白磷酸酶（PP1c）的催化亚基结合，并在体外抑制其活性。重组PP1c在几个生化标准上与天然PP1c不同，包括对Mn(2+)的需求、对钒酸盐的敏感性以及对磷酸对硝基苯酯（pNPP）的磷酸酶活性。I-2能在体外将重组PP1c转化为类似天然的活性。因此有人提出，I-2在体内可能作为PP1的分子伴侣发挥作用。我们在一个用于筛选与PP1c结合蛋白的双杂交实验中鉴定出了一种果蝇同源物（I-2Dm）。I-2Dm的序列与I-2的序列有35%的同一性，而催化亚基本身在果蝇和人类中则有>85%的同一性；然而，我们发现I-2的许多生化特性是保守的。与I-2一样，I-2Dm能将重组PP1c转化为类似天然的活性。这有力地表明，这种能力是I-2和I-2Dm的一个基本的、保守的作用。
