ER membrane complex (EMC): Structure, functions, and roles in diseases

The endoplasmic reticulum (ER) is the largest membrane system in eukaryotic cells and is the primary site for the biosynthesis of lipids and carbohydrates, as well as for the folding, assembly, modification, and transport of secreted and integrated membrane proteins. The ER membrane complex (EMC) on the ER membrane is an ER multiprotein complex that affects the quality control of membrane proteins, which is abundant and widely preserved. Its disruption has been found to affect a wide range of processes, including protein and lipid synthesis, organelle communication, endoplasmic reticulum stress, and viral maturation, and may lead to neurodevelopmental disorders and cancer. Therefore, EMC has attracted the attention of many scholars and become a hot field. In this paper, we summarized the main contributions of the research of EMC in the past nearly 15 years, and reviewed the structure and function of EMC as well as its related diseases. We hope this review will promote further progress of research on EMC.

2.8-Å crystal structure of Escherichia coli YidC revealing all core regions, including flexible C2 loop

YidC/Alb3/Oxa1 family proteins are involved in the insertion and assembly of membrane proteins. The core five transmembrane regions of YidC, which are conserved in the protein family, form a positively charged cavity open to the cytoplasmic side. The cavity plays an important role in membrane protein insertion. In all reported structural studies of YidC, the second cytoplasmic loop (C2 loop) was disordered, limiting the understanding of its role. Here, we determined the crystal structure of YidC including the C2 loop at 2.8 Å resolution with R/R_free = 21.8/27.5. This structure and subsequent molecular dynamics simulation indicated that the intrinsic flexible C2 loop covered the positively charged cavity. This crystal structure provides the coordinates of the complete core region including the C2 loop, which is valuable for further analyses of YidC.