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热休克蛋白70(hsp 70)多基因家族是已知的最保守基因。78kDa葡萄糖调节蛋白(Grp78)即免疫球蛋白重链结合蛋白(Bip)为hsp70蛋白家族的一成员。但哺乳动物的Grp78的合成不受热的影响,属组成型合成。刺激Grp78表达的因素包括能抑制蛋白质糖基化的衣霉素、葡萄糖缺乏以及钙离子载体。Grp78不同于其它hsp70蛋白质的主要特征包括一段疏水信号序列,利用Grp78跨膜进入内质网(ER)腔,羧基端的ER保留信号(KDEL),使蛋白质固定在ER腔内。
The multi-gene family of heat shock protein 70 (hsp 70) is the most conserved gene known. The 78 kDa glucose regulatory protein (Grp78), an immunoglobulin heavy chain binding protein (Bip), is a member of the hsp70 protein family. However, the synthesis of mammalian Grp78 is not affected by heat and is a constitutive synthesis. Factors that stimulate Grp78 expression include tunicamycin, glucose deficiency, and calcium ionophores that inhibit protein glycosylation. The key features of Grp78, which is different from other hsp70 proteins, include a hydrophobic signal sequence that uses Grp78 transmembrane access to the ER lumen and a carboxyterminal ER retention signal (KDEL) to immobilize the protein in the ER lumen.