Rouault Morgane, Bollinger James G, Lazdunski Michel, Gelb Michael H, Lambeau Gérard
Institut de Pharmacologie Moléculaire et Cellulaire, CNRS-UMR 6097, 660 route des Lucioles, Sophia Antipolis, 06560 Valbonne, France.
Biochemistry. 2003 Oct 7;42(39):11494-503. doi: 10.1021/bi0349930.
An increasing number of mammalian secreted phospholipases A(2) (sPLA(2)s) has been identified over the past few years. Here, we report the identification and recombinant expression of a novel sPLA(2)-like protein in mouse and human species that has been called group XIIB (GXIIB). The mature protein has a molecular mass of 19.7 kDa and structural features similar to those of the previously identified GXII sPLA(2), now called GXIIA. Strikingly, the GXIIB sPLA(2) has a mutation in the active site, replacing the canonical histidine by a leucine, suggesting that this sPLA(2) is catalytically inactive. Recombinant expression of human (hGXIIB) and mouse (mGXIIB) sPLA(2)s in Escherichia coli indicates that GXIIB sPLA(2)s display no measurable lipolytic activity on various types of phospholipid substrates. Furthermore, these sPLA(2)-like proteins display relatively weak affinity to phospholipid vesicles. Binding experiments indicate that these proteins are also unable to bind to the well-known M-type sPLA(2) receptor. The RNA tissue distribution of GXIIB sPLA(2)s is distinct from that of other sPLA(2)s including the homologous GXIIA. Strong expression was observed in liver, small intestine, and kidney in both human and mouse species. Interestingly, the expression of the novel sPLA(2) is dramatically decreased in human tumors from the same tissues. The absence of enzymatic activity suggests that the GXIIB sPLA(2)-like proteins probably exert their biological roles by acting as ligands for as yet unidentified receptors.
在过去几年中，已鉴定出越来越多的哺乳动物分泌型磷脂酶A2（sPLA2）。在此，我们报告在小鼠和人类中鉴定并重组表达了一种新型的类sPLA2蛋白，它被称为XIIB组（GXIIB）。成熟蛋白的分子量为19.7 kDa，其结构特征与先前鉴定的GXII sPLA2（现称为GXIIA）相似。引人注目的是，GXIIB sPLA2在活性位点发生了突变，将典型的组氨酸替换为亮氨酸，这表明该sPLA2无催化活性。人（hGXIIB）和小鼠（mGXIIB）sPLA2在大肠杆菌中的重组表达表明，GXIIB sPLA2对各种类型的磷脂底物均无明显的脂解活性。此外，这些类sPLA2蛋白对磷脂囊泡的亲和力相对较弱。结合实验表明，这些蛋白也无法与著名的M型sPLA2受体结合。GXIIB sPLA2的RNA组织分布与包括同源GXIIA在内的其他sPLA2不同。在人类和小鼠的肝脏、小肠和肾脏中均观察到强表达。有趣的是，在来自相同组织的人类肿瘤中，这种新型sPLA2的表达显著降低。酶活性的缺失表明，GXIIB类sPLA2蛋白可能通过作为尚未鉴定的受体的配体来发挥其生物学作用。
