Aggensteiner M, Stricker R, Reiser G
Institut für Neurobiochemie der Otto-von Guericke-Universität Magdeburg, Medizinische Fakultät, Leipziger Str. 44, 39120 Magdeburg, Germany.
Biochim Biophys Acta. 1998 Sep 8;1387(1-2):117-28. doi: 10.1016/s0167-4838(98)00113-7.
Inositol(1,3,4,5)tetrakisphosphate (InsP4) and phosphatidylinositol(3,4,5)trisphosphate (PtdInsP3) are two potential second messengers with a still largely unknown mode of action. We recently cloned the 42 kDa protein p42IP4 previously purified from pig cerebellum, which binds InsP4 (Kd approximately 2 nM) and PtdInsP3 with comparable affinities (Stricker et al., FEBS Lett. 405 (1997) 229). The protein p42IP4 (pig) is highly homologous to centaurin-alpha, a larger protein of 46 kDa, derived from a rat brain cDNA library clone (Hammonds-Odie et al., J. Biol. Chem. 271 (1996) 18859). Here we investigated whether also p42IP4 is expressed in rat brain and how it might be related to centaurin-alpha. When we carried out RT-PCR using mRNA from brain of rats of different ages we obtained several clones corresponding to p42IP4, but not to centaurin-alpha. The existence of p42IP4 in rat brain is supported by the following findings: (1) biochemical analysis of the purified rat brain protein shows inositol phosphate ligand affinities identical to those of the protein from other species; (2) Western blot analysis of rat brain membrane fractions using a peptide-specific antiserum revealed only the 42 kDa protein (p42IP4), but did not give evidence for the occurrence of a larger 46 kDa centaurin-alpha-like protein in rat brain; and (3) the amino acid sequences deduced from p42IP4 cDNA are highly homologous in several species and are confirmed by protein fragment microsequences. Thus, p42IP4 from rat brain which has two pleckstrin homology domains is a protein largely conserved between different species and most likely has an important function in inositol phosphate or inositol lipid signal transduction.
肌醇（1,3,4,5）四磷酸（InsP4）和磷脂酰肌醇（3,4,5）三磷酸（PtdInsP3）是两种潜在的第二信使，其作用方式在很大程度上仍不清楚。我们最近克隆了先前从猪小脑纯化的42 kDa蛋白p42IP4，它以相当的亲和力结合InsP4（解离常数约为2 nM）和PtdInsP3（斯特里克等人，《欧洲生物化学学会联合会快报》405 (1997) 229）。蛋白p42IP4（猪）与centaurin-α高度同源，centaurin-α是一种更大的46 kDa蛋白，源自大鼠脑cDNA文库克隆（哈蒙兹-奥迪等人，《生物化学杂志》271 (1996) 18859）。在此我们研究了p42IP4是否也在大鼠脑中表达以及它与centaurin-α可能有怎样的关系。当我们使用来自不同年龄大鼠脑的mRNA进行逆转录聚合酶链反应（RT-PCR）时，我们获得了几个与p42IP4对应的克隆，但没有与centaurin-α对应的克隆。大鼠脑中存在p42IP4得到了以下发现的支持：（1）对纯化的大鼠脑蛋白进行生化分析显示，其肌醇磷酸配体亲和力与来自其他物种的蛋白相同；（2）使用肽特异性抗血清对大鼠脑膜部分进行蛋白质印迹分析仅显示了42 kDa蛋白（p42IP4），但没有证据表明大鼠脑中存在更大的46 kDa的centaurin-α样蛋白；（3）从p42IP4 cDNA推导的氨基酸序列在几个物种中高度同源，并通过蛋白质片段微序列得到证实。因此，来自大鼠脑的具有两个普列克底物蛋白同源结构域的p42IP4是一种在不同物种间高度保守的蛋白，很可能在肌醇磷酸或肌醇脂质信号转导中具有重要功能。
