ERP27 (endoplasmic reticulum protein 27) is a non-catalytic member of the protein disulfide isomerase (PDI) family that plays a crucial role in protein folding quality control within the endoplasmic reticulum 1. The protein consists of two thioredoxin-fold domains homologous to the non-catalytic b and b' domains of PDI, with extensive interdomain flexibility allowing the domains to flex independently 2. ERP27 specifically binds unfolded protein substrates through a hydrophobic pocket in its C-terminal domain and undergoes significant conformational changes upon substrate binding 1. The protein interacts with other ER chaperones, including ERp57, suggesting it functions as part of a broader protein folding network 1. ERP27 demonstrates clinical significance as a biomarker across multiple cancers, including pancreatic ductal adenocarcinoma, colorectal cancer, and thyroid cancer, where its expression levels correlate with disease prognosis and progression 3456. Additionally, ERP27 expression is altered in response to cigarette smoking exposure, contributing to COPD progression discriminant models 7. These findings establish ERP27 as both a critical component of ER protein quality control mechanisms and a promising biomarker for various disease conditions.