Sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) pumps Ca2+ from the cytosol into the ER and maintains the cellular calcium homeostasis. Herein, we present cryo–electron microscopy (cryo-EM) structures of human SERCA2b in E1∙2Ca2+–adenylyl methylenediphosphonate (AMPPCP) and E2-BeF3− states at 2.9- and 2.8-Å resolutions, respectively. The structures revealed that the luminal extension tail (LE) characteristic of SERCA2b runs parallel to the lipid-water boundary near the luminal ends of transmembrane (TM) helices TM10 and TM7 and approaches the luminal loop flanked by TM7 and TM8. While the LE served to stabilize the cytosolic and TM domain arrangement of SERCA2b, deletion of the LE rendered the overall conformation resemble that of SERCA1a and SERCA2a and allowed multiple conformations. Thus, the LE appears to play a critical role in conformational regulation in SERCA2b, which likely explains the different kinetic properties of SERCA2b from those of other isoforms lacking the LE.

Sarco/endoplasmic reticulum Ca 2+ -ATPase (SERCA) 2b is a ubiquitous SERCA family member that conducts Ca 2+ uptake from the cytosol to the ER. Herein, we present a 3.3 A resolution cryoelectron microscopy (cryo-EM) structure of human SERCA2b in the E1Á2Ca 2+ state, revealing a new conformation for Ca 2+ -bound SERCA2b with a much closer arrangement of cytosolic domains than in the previously reported crystal structure of Ca 2+ -bound SERCA1a. Multiple conformations generated by 3D classification of cryo-EM maps reflect the intrinsically dynamic nature of the cytosolic domains in this state. Notably, ATP binding residues of SERCA2b in the E1Á2Ca 2+ state are located at similar positions to those in the E1Á2Ca 2+ -ATP state; hence, the cryo-EM structure likely represents a preformed state immediately prior to ATP binding. Consistently, a SERCA2b mutant with an interdomain disulfide bridge that locks the closed cytosolic domain arrangement displayed significant autophosphorylation activity in the presence of Ca 2+ . We propose a novel mechanism of ATP binding to SERCA2b.

Echovirus 3 (E3), a serotype of human enterovirus B (HEV-B), causes severe diseases in infants. Here, we determined the structures of E3 with a monoclonal antibody (MAb) 6D10 by cryo-EM to comprehensively understand the specificities and the immunological characteristic of this serotype. The solved cryo-EM structures of the F-, A-, and E-particles of E3 bound with 6D10 revealed the structural features of the virus–antibody interface. Importantly, the structures of E-particles bound with 6D10 revealed for the first time the nature of the C-terminus of VP1 for HEV-Bs at the structural level. The highly immunogenic nature of this region in the E-particles provides new strategies for vaccine development for HEV-Bs.

SARS-CoV-2 S protein-mediated fusion is thought to involve the interaction of the membrane-distal, or N-terminal heptad repeat (NHR) (termed HR1) of the cleaved S2 segment of the protein, and the membrane-proximal, or C-terminal heptad repeat (CHR) (termed HR2) regions of the protein. Following the observations of Xia et al (Xia S, Liu M, Wang C, Xu W, Lan Q, Feng S, Qi F, Bao L, Du L, Liu S, Qin C, Sun F, Shi Z, Zhu Y, Jiang S, Lu L. Cell Res. 2020b Apr;30(4):343-355), we examined the fusion inhibitory activity of a PEGylated HR2-derived peptide and its palmitoylated derivative, using a pseudovirus infection assay. The latter peptide caused a 76% reduction in fusion activity at 10 μM. Our results suggest that small variations in peptide derivatization and differences in the membrane composition of pseudovirus preparations may affect the inhibitory potency of HR2-derived peptides.