Angiotensin-converting enzyme 2 (ACE2) is the cellular receptor for SARS coronavirus (SARS-CoV) and the new coronavirus (SARS-CoV-2) that is causing the serious epidemic COVID-19. Here we present cryo-EM structures of full-length human ACE2, in the presence of a neutral amino acid transporter B 0 AT1, with or without the receptor binding domain (RBD) of the surface spike glycoprotein (S protein) of SARS-CoV-2, both at an overall resolution of 2.9 Å, with a local resolution of 3.5 Å at the ACE2-RBD interface. The ACE2-B 0 AT1 complex is assembled as a dimer of heterodimers, with the Collectrin-like domain (CLD) of ACE2 mediating homo-dimerization. The RBD is recognized by the extracellular peptidase domain (PD) of ACE2 mainly through polar residues. These findings provide important insights to the molecular basis for coronavirus recognition and infection.

Developing therapeutics against SARS-CoV-2 could be guided by the distribution of epitopes, not only on the receptor binding domain (RBD) of the Spike (S) protein, but also across the full Spike (S) protein. We isolated and characterized monoclonal antibodies (mAbs) from ten convalescent COVID-19 patients. Three mAbs showed neutralizing activities against authentic SARS-CoV-2. An mAb, named 4A8, exhibits high neutralization potency against both authentic and pseudotyped SARS-CoV-2, but does not bind the RBD. We defined the epitope of 4A8 as the N terminal domain (NTD) of the S protein by determining its cryo-EM structure in complex with the S protein to an overall resolution of 3.1 Angstrom and local resolution of 3.3 Angstrom for the 4A8-NTD interface. This points to the NTD as a promising target for therapeutic mAbs against COVID-19.

† These authors contribute equally to this work.Exosomes play important roles in many physiological and pathological processes. However, the exosome-cell interaction mode and the intracellular trafficking pathway of exosomes in their recipient cells remain unclear. Here, we report that exosomes derived from K562 or MT4 cells are internalized more efficiently by phagocytes than by non-phagocytic cells. Most exosomes were observed attached to the plasma membrane of non-phagocytic cells, while in phagocytic cells these exosomes were found to enter via phagocytosis. Specifically, they moved to phagosomes together with phagocytic polystyrene carboxylate-modified latex beads (biospheres) and were further sorted into phagolysosomes. Moreover, exosome internalization was dependent on the actin cytoskeleton and phosphatidylinositol 3-kinase, and could be inhibited by the knockdown of dynamin2 or overexpression of a dominant-negative form of dynamin2. Further, antibody pretreatment assays demonstrated that tim4 but not tim1 was involved in exosomes uptake. We also found that exosomes did not enter the internalization pathway involving caveolae, macropinocytosis and clathrin-coated vesicles. Our observation that the cellular uptake of exosomes occurs through phagocytosis has important implications for exosome-cell interactions and the exosome intracellular trafficking pathway.

The voltage-gated calcium (Ca) channels convert membrane electrical signals to intracellular Ca-mediated events. Among the ten subtypes of Ca channel in mammals, Ca1.1 is specified for the excitation-contraction coupling of skeletal muscles. Here we present the cryo-electron microscopy structure of the rabbit Ca1.1 complex at a nominal resolution of 3.6 Å. The inner gate of the ion-conducting α1-subunit is closed and all four voltage-sensing domains adopt an 'up' conformation, suggesting a potentially inactivated state. The extended extracellular loops of the pore domain, which are stabilized by multiple disulfide bonds, form a windowed dome above the selectivity filter. One side of the dome provides the docking site for the α2δ-1-subunit, while the other side may attract cations through its negative surface potential. The intracellular I-II and III-IV linker helices interact with the β-subunit and the carboxy-terminal domain of α1, respectively. Classification of the particles yielded two additional reconstructions that reveal pronounced displacement of β and adjacent elements in α1. The atomic model of the Ca1.1 complex establishes a foundation for mechanistic understanding of excitation-contraction coupling and provides a three-dimensional template for molecular interpretations of the functions and disease mechanisms of Ca and Na channels.

Voltage-gated sodium (Na) channels, which are responsible for action potential generation, are implicated in many human diseases. Despite decades of rigorous characterization, the lack of a structure of any human Na channel has hampered mechanistic understanding. Here, we report the cryo-electron microscopy structure of the human Na1.4-β1 complex at 3.2-Å resolution. Accurate model building was made for the pore domain, the voltage-sensing domains, and the β1 subunit, providing insight into the molecular basis for Na permeation and kinetic asymmetry of the four repeats. Structural analysis of reported functional residues and disease mutations corroborates an allosteric blocking mechanism for fast inactivation of Na channels. The structure provides a path toward mechanistic investigation of Na channels and drug discovery for Na channelopathies.