Loijens J C, Anderson R A
Program in Cellular and Molecular Biology and Department of Pharmacology, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA.
J Biol Chem. 1996 Dec 20;271(51):32937-43. doi: 10.1074/jbc.271.51.32937.
Phosphatidylinositol-4-phosphate 5-kinases (PIP5K) synthesize phosphatidylinositol-4,5-bisphosphate, a key precursor in phosphoinositide signaling that also regulates some proteins and cellular processes directly. Two distinct PIP5Ks have been characterized in erythrocytes, the 68-kDa type I (PIP5KI) and 53-kDa type II (PIP5KII) isoforms. Using peptide sequences from the erythroid 68-kDa PIP5KI, we have isolated cDNAs encoding PIP5KIalpha from human brain. Partial cDNAs obtained for a second isoform, PIP5KIbeta, established that the human STM7 gene encoded a previously unrecognized PIP5KI. However, the peptide sequences demonstrated that erythroid PIP5KI corresponded to PIP5KIalpha. Recombinant, bacterially expressed PIP5KIalpha possessed PIP5K activity and was immunoreactive with erythroid PIP5KI antibodies. By Northern analysis, PIP5KIalpha and PIP5KIbeta had wide tissue distributions, but their expression levels differed greatly. PIP5KIs had homology to the kinase domains of PIP5KIIalpha, yeast Mss4p and Fab1p, and a new Caenorhabditis elegans Fab1-like protein identified in the data base. These new isoforms have refined the sequence requirements for PIP5K activity and, potentially, regulation of these enzymes. Furthermore, the limited homology between PIP5KIs and PIP5KIIalpha, which was almost exclusively within the kinase domain core, provided a molecular basis for distinction between type I and II PIP5Ks.
磷脂酰肌醇-4-磷酸5-激酶（PIP5K）可合成磷脂酰肌醇-4,5-二磷酸，这是磷酸肌醇信号传导中的一种关键前体物质，它还能直接调节某些蛋白质和细胞过程。在红细胞中已鉴定出两种不同的PIP5K，即68 kDa的I型（PIP5KI）和53 kDa的II型（PIP5KII）同工型。利用来自红细胞68 kDa PIP5KI的肽序列，我们从人脑中分离出了编码PIP5KIα的cDNA。为第二种同工型PIP5KIβ获得的部分cDNA证实，人类STM7基因编码一种先前未被识别的PIP5KI。然而，肽序列表明红细胞PIP5KI与PIP5KIα相对应。重组的、细菌表达的PIP5KIα具有PIP5K活性，并且与红细胞PIP5KI抗体发生免疫反应。通过Northern分析，PIP5KIα和PIP5KIβ具有广泛的组织分布，但它们的表达水平差异很大。PIP5KIs与PIP5KIIα、酵母Mss4p和Fab1p的激酶结构域以及数据库中鉴定出的一种新的秀丽隐杆线虫Fab1样蛋白具有同源性。这些新的同工型完善了PIP5K活性以及这些酶潜在调控的序列要求。此外，PIP5KIs与PIP5KIIα之间有限的同源性几乎完全存在于激酶结构域核心内，这为区分I型和II型PIP5K提供了分子基础。
