Tanikawa Yuya, Kanemura Shingo, Ito Dai, Lin Yuxi, Matsusaki Motonori, Kuroki Kimiko, Yamaguchi Hiroshi, Maenaka Katsumi, Lee Young-Ho, Inaba Kenji, Okumura Masaki
School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan.
Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, 6-3 Aramakiaza Aoba, Aoba-ku, Sendai 980-8578, Japan.
Molecules. 2021 May 11;26(10):2853. doi: 10.3390/molecules26102853.
ERp57, a member of the protein disulfide isomerase family, is a ubiquitous disulfide catalyst that functions in the oxidative folding of various clients in the mammalian endoplasmic reticulum (ER). In concert with ER lectin-like chaperones calnexin and calreticulin (CNX/CRT), ERp57 functions in virtually all folding stages from co-translation to post-translation, and thus plays a critical role in maintaining protein homeostasis, with direct implication for pathology. Here, we present mechanisms by which Ca regulates the formation of the ERp57-calnexin complex. Biochemical and isothermal titration calorimetry analyses revealed that ERp57 strongly interacts with CNX via a non-covalent bond in the absence of Ca. The ERp57-CNX complex not only promoted the oxidative folding of human leukocyte antigen heavy chains, but also inhibited client aggregation. These results suggest that this complex performs both enzymatic and chaperoning functions under abnormal physiological conditions, such as Ca depletion, to effectively guide proper oxidative protein folding. The findings shed light on the molecular mechanisms underpinning crosstalk between the chaperone network and Ca.
内质网蛋白57（ERp57）是蛋白质二硫键异构酶家族的一员，是一种普遍存在的二硫键催化剂，在哺乳动物内质网（ER）中参与多种底物的氧化折叠过程。与内质网凝集素样伴侣钙连蛋白和钙网蛋白（CNX/CRT）协同作用，ERp57几乎在从共翻译到翻译后修饰的所有折叠阶段都发挥作用，因此在维持蛋白质稳态中起关键作用，这对病理学有直接影响。在此，我们阐述了钙离子调节ERp57-钙连蛋白复合物形成的机制。生化分析和等温滴定量热法分析表明，在没有钙离子的情况下，ERp57通过非共价键与CNX强烈相互作用。ERp57-CNX复合物不仅促进了人类白细胞抗原重链的氧化折叠，还抑制了底物聚集。这些结果表明，在诸如钙离子耗竭等异常生理条件下，该复合物同时发挥酶促和伴侣功能，以有效地引导蛋白质进行正确的氧化折叠。这些发现揭示了伴侣网络与钙离子之间相互作用的分子机制。
