Labunskyy Vyacheslav M, Ferguson Andrew D, Fomenko Dmitri E, Chelliah Yogarany, Hatfield Dolph L, Gladyshev Vadim N
Department of Biochemistry, University of Nebraska, Lincoln, 68588, USA.
J Biol Chem. 2005 Nov 11;280(45):37839-45. doi: 10.1074/jbc.M508685200. Epub 2005 Aug 29.
Selenium is an essential trace element with potent cancer prevention activity in mammals. The 15-kDa selenoprotein (Sep15) has been implicated in the chemopreventive effect of dietary selenium. Although the precise function of Sep15 remains elusive, Sep15 co-purifies with UDP-glucose:glycoprotein glucosyltransferase (GT), an essential regulator of quality control mechanisms within the endoplasmic reticulum. Recent studies identified two GT and two Sep15 homologues in mammals. We characterize interactions between these protein families in this report. Sep15 and GT form a tight 1:1 complex, and these interactions are conserved between mammals and fruit flies. In mammalian cells, Sep15 co-immunoprecipitates with both GT isozymes. In contrast, a Sep15 homologue, designated selenoprotein M (SelM), does not form a complex with GT. Sequence analysis of members of the Sep15 family identified a novel N-terminal cysteine-rich domain in Sep15 that is absent in SelM. This domain contains six conserved cysteine residues that form two CxxC motifs that do not coordinate metal ions. If this domain is deleted or the cysteines are mutated, Sep15 no longer forms a complex with GT. Conversely, if the cysteine-rich domain of Sep15 is fused to the N-terminus of SelM, the resulting chimera is capable of binding GT. These data indicate that the cysteine-rich domain of Sep15 exclusively mediates protein-protein interactions with GT.
硒是一种必需的微量元素，在哺乳动物中具有强大的癌症预防活性。15 kDa的硒蛋白（Sep15）与膳食硒的化学预防作用有关。尽管Sep15的确切功能仍不清楚，但它与UDP-葡萄糖：糖蛋白葡糖基转移酶（GT）共同纯化，GT是内质网内质量控制机制的重要调节因子。最近的研究在哺乳动物中鉴定出两种GT和两种Sep15同源物。在本报告中，我们描述了这些蛋白质家族之间的相互作用。Sep15和GT形成紧密的1:1复合物，并且这些相互作用在哺乳动物和果蝇之间是保守的。在哺乳动物细胞中，Sep15与两种GT同工酶都能进行共免疫沉淀。相比之下，一种名为硒蛋白M（SelM）的Sep15同源物不与GT形成复合物。对Sep15家族成员的序列分析在Sep15中鉴定出一个新的富含半胱氨酸的N端结构域，而SelM中没有该结构域。该结构域包含六个保守的半胱氨酸残基，形成两个不与金属离子配位的CxxC基序。如果删除该结构域或使半胱氨酸发生突变，Sep15就不再与GT形成复合物。相反，如果将Sep15的富含半胱氨酸结构域融合到SelM的N端，得到的嵌合体能够结合GT。这些数据表明，Sep15的富含半胱氨酸结构域专门介导与GT的蛋白质-蛋白质相互作用。
