Blocki F A, Ellis L B, Wackett L P
Department of Biochemistry, College of Biological Sciences, University of Minnesota, St. Paul 55108.
Protein Sci. 1993 Dec;2(12):2095-102. doi: 10.1002/pro.5560021210.
MIF proteins are mammalian polypeptides of approximately 13,000 molecular weight. This class includes human macrophage migration inhibitory factor (MIF), a rat liver protein that has glutathione S-transferase (GST) activity (TRANSMIF), and the mouse delayed early response gene 6 (DER6) protein. MIF proteins were previously linked to GSTs by demonstrating transferase activity and observing N-terminal sequence homology with a mu-class GST (Blocki, F.A., Schlievert, P.M., & Wackett, L.P., 1992, Nature 360, 269-270). In this study, MIF proteins are shown to be structurally related to the theta class of GSTs. This is established in three ways. First, unique primary sequence patterns are developed for each of the GST gene classes. The patterns identify the three MIF proteins as theta-like transferase homologs. Second, pattern analysis indicates that GST members of the theta class contain a serine residue in place of the N-terminal tyrosine that is implicated in glutathione deprotonation and activation in GSTs of known structure (Liu, S., et al., 1992, J. Biol. Chem. 267, 4296-4299). The MIF proteins contain a threonine at this position. Third, polyclonal antibodies raised against recombinant human MIF cross-react on Western blots with rat theta GST but not with alpha and mu GSTs. That MIF proteins have glutathione-binding ability may provide a common structural key toward understanding the varied functions of this widely distributed emerging gene family. Because theta is thought to be the most ancient evolutionary GST class, MIF proteins may have diverged early in evolution but retained a glutathione-binding domain.
巨噬细胞移动抑制因子（MIF）蛋白是分子量约为13,000的哺乳动物多肽。这一类包括人类巨噬细胞移动抑制因子（MIF）、一种具有谷胱甘肽S-转移酶（GST）活性的大鼠肝脏蛋白（TRANSMIF）以及小鼠延迟早期反应基因6（DER6）蛋白。先前通过证明转移酶活性并观察与μ类GST的N端序列同源性，将MIF蛋白与GST联系起来（Blocki, F.A., Schlievert, P.M., & Wackett, L.P., 1992, 《自然》360, 269 - 270）。在本研究中，MIF蛋白被证明在结构上与θ类GST相关。这通过三种方式得以确立。首先，为每个GST基因类开发了独特的一级序列模式。这些模式将三种MIF蛋白鉴定为类θ转移酶同源物。其次，模式分析表明，θ类的GST成员在已知结构的GST中与谷胱甘肽去质子化和激活有关的N端酪氨酸位置含有一个丝氨酸残基（Liu, S., 等人, 1992, 《生物化学杂志》267, 4296 - 4299）。MIF蛋白在该位置含有一个苏氨酸。第三，针对重组人MIF产生的多克隆抗体在蛋白质印迹上与大鼠θGST发生交叉反应，但不与α和μGST发生交叉反应。MIF蛋白具有谷胱甘肽结合能力这一点可能为理解这个广泛分布的新兴基因家族的多种功能提供一个共同的结构关键。由于θ被认为是最古老的进化GST类，MIF蛋白可能在进化早期就发生了分化，但保留了一个谷胱甘肽结合结构域。
