Darby N J, Kemmink J, Creighton T E
European Molecular Biology Laboratory, Heidelberg, Germany.
Biochemistry. 1996 Aug 13;35(32):10517-28. doi: 10.1021/bi960763s.
Protein disulfide isomerase (PDI) appears on the basis of its primary structure to be a multidomain protein, but the number and nature of the domains has been uncertain. Two of the domains, a and a', which are homologous to thioredoxin and active in catalysis of disulfide bond formation, have been identified and characterized previously. Sections of the N-terminal half of the PDI sequence have been expressed and the limits of their folded structures delineated by limited proteolysis. In addition to the a-domain, the boundaries of a domain with no activity on thiol/disulfide groups, designated b, have been identified. This domain has been produced independently; its cooperative unfolding transition and its CD and NMR spectra confirm that it is an autonomously folded structure in isolation and when part of PDI. Fusion of the b-domain to the a-domain, as occurs naturally in the first half of PDI, did not alter substantially the catalytic activity of the a-domain. It still catalyzes only a subset of the thiol/disulfide exchange reactions of intact PDI and has a reduced ability to catalyze protein disulfide rearrangements. The a- and b-domains account structurally for virtually all of the first half of the PDI polypeptide chain, and it is very unlikely that there exists a proposed third domain homologous to the estrogen receptor. The b-domain exhibits some sequence homology to calsequestrin, a calcium binding protein from the sarcoplasmic reticulum of muscle.
蛋白质二硫键异构酶（PDI）基于其一级结构似乎是一种多结构域蛋白，但结构域的数量和性质一直不确定。其中两个结构域，即与硫氧还蛋白同源且在二硫键形成催化中具有活性的a和a'结构域，此前已被鉴定和表征。PDI序列N端一半的片段已被表达，其折叠结构的边界通过有限蛋白酶解来划定。除了a结构域外，还鉴定出了一个对硫醇/二硫键无活性的结构域的边界，称为b结构域。该结构域已被独立产生；其协同解折叠转变以及其圆二色光谱和核磁共振光谱证实，它在单独存在时以及作为PDI的一部分时都是自主折叠的结构。b结构域与a结构域的融合，就像在PDI前半部分自然发生的那样，并没有实质性改变a结构域的催化活性。它仍然只催化完整PDI的硫醇/二硫键交换反应的一个子集，并且催化蛋白质二硫键重排的能力降低。a和b结构域在结构上几乎占了PDI多肽链前半部分的全部，并且极不可能存在一个与雌激素受体同源的、推测的第三个结构域。b结构域与肌浆网钙结合蛋白钙网蛋白表现出一些序列同源性。
