Lei G, Arany I, Tyring S K, Brysk H, Brysk M M
Department of Dermatology, University of Texas Medical Branch, Galveston, Texas, 77555, USA.
Arch Biochem Biophys. 1998 Jul 15;355(2):160-4. doi: 10.1006/abbi.1998.0735.
Zinc-alpha 2-glycoprotein (Zn alpha 2gp) is widely distributed in body fluids and in various epithelia; its gene has been completely sequenced, but its function has long remained elusive. We have found that Zn alpha 2gp has RNase activity, comparable to onconase but two orders of magnitude less than RNase A. The RNase activity of Zn alpha 2gp is characterized by maxima in pH at 7.5, in ionic strength at 50 mM NaCl, and in temperature at 60 degreesC. It is strongly inhibited by ZnCl2, but unaffected by MgCl2. It is partially inactivated (down to 20%) by the placental RNase inhibitor. On synthetic polyribonucleotide substrates, the RNase activity of Zn alpha 2gp is specific for pyrimidine residues [poly(C) and poly(U) equally] and cleaves only single-stranded RNA. For onconase, it has been demonstrated that the RNase activity depends on pyroglutamic acid (pyr 1) as the N-terminus; Zn alpha 2gp also has pyr 1, while RNase A does not. Alignment of the amino acid sequences of Zn alpha 2gp and onconase or RNase A reveals only modest matches. Despite the more substantial overall structural homology of Zn alpha 2gp to class I major histocompatibility complex proteins, Zn alpha 2gp has not been proven to be associated with the immune response and, conversely, we could not detect RNase activity in six class I HLA heavy chains.
锌-α2-糖蛋白（Znα2gp）广泛分布于体液和各种上皮组织中；其基因已被完全测序，但其功能长期以来一直难以捉摸。我们发现Znα2gp具有核糖核酸酶活性，与癌胚核糖核酸酶相当，但比核糖核酸酶A低两个数量级。Znα2gp的核糖核酸酶活性的特点是在pH值为7.5、离子强度为50 mM NaCl、温度为60℃时活性最高。它受到ZnCl2的强烈抑制，但不受MgCl2的影响。它被胎盘核糖核酸酶抑制剂部分失活（降至20%）。在合成多聚核糖核苷酸底物上，Znα2gp的核糖核酸酶活性对嘧啶残基具有特异性（对聚（C）和聚（U）同等），并且仅切割单链RNA。对于癌胚核糖核酸酶，已证明其核糖核酸酶活性取决于焦谷氨酸（pyr 1）作为N端；Znα2gp也有pyr 1，而核糖核酸酶A没有。Znα2gp与癌胚核糖核酸酶或核糖核酸酶A的氨基酸序列比对仅显示适度匹配。尽管Znα2gp与I类主要组织相容性复合体蛋白在整体结构上有更显著的同源性，但尚未证明Znα2gp与免疫反应相关，相反，我们在六种I类HLA重链中未检测到核糖核酸酶活性。
