How lethal coronaviruses engage hosts: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is closely related to the deadly coronaviruses SARS-CoV-1 and Middle East respiratory syndrome coronavirus (MERS-CoV). Considerable efforts are focused on developing treatments, and therapies that work across coronaviruses would be particularly valuable. Shedding light on the host factors hijacked by the viruses, Gordon et al. mapped the interactions between viral and human proteins for SARS-CoV-2, SARS-CoV-1, and MERS-CoV; analyzed the localization of viral proteins in human cells; and used genetic screening to identify host factors that either enhance or inhibit viral infection. For a subset of the interactions essential for the virus life cycle, the authors determined the cryo–electron microscopy structures and mined patient data to understand how targeting host factors may be relevant to clinical outcomes. Science , this issue p. eabe9403

Holding kinases at the ready: About 60% of kinases only reach their active state in the presence of the molecular chaperone Hsp90 and its co-chaperone Cdc37. It is unclear how the chaperones facilitate kinase function or why only some kinases are chaperone-dependent. Verba et al. determined a 3.9 Å cryo–electron microscopy structure of Hsp90:Cdc37 in complex with the kinase Cdk4. Together, Hsp90 and Cdc37 trap the kinase in an open, partially unfolded state. Taking on this state probably has direct functional benefits. Science , this issue p. 1542

Nanobodies that neutralize: Monoclonal antibodies that bind to the spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) show therapeutic promise but must be produced in mammalian cells and need to be delivered intravenously. By contrast, single-domain antibodies called nanobodies can be produced in bacteria or yeast, and their stability may enable aerosol delivery. Two papers now report nanobodies that bind tightly to spike and efficiently neutralize SARS-CoV-2 in cells. Schoof et al. screened a yeast surface display of synthetic nanobodies and Xiang et al. screened anti-spike nanobodies produced by a llama. Both groups identified highly potent nanobodies that lock the spike protein in an inactive conformation. Multivalent constructs of selected nanobodies achieved even more potent neutralization. Science , this issue p. 1473 , p. 1479

Experimental studies of protein folding are hampered by the fact that only low-resolution structural data can be obtained with sufficient temporal resolution. Molecular dynamics simulations offer a complementary approach, providing extremely high-resolution spatial and temporal data on folding processes. However, at present, such simulations are limited in several respects, including the inability of molecular dynamics force fields to completely reproduce the true potential energy surfaces of proteins, the need for simulations to extend to the millisecond timescale for the folding of many proteins and the difficulty inherent in obtaining sufficient sampling to properly characterize the extremely heterogeneous folding processes and then analysing those data efficiently. We review recent progress in the simulation of three common model systems for protein folding, and discuss how advances in technology and theory are allowing protein-folding simulations to address their present shortcomings.

The mechanosensitive channel of large conductance, which serves as a model system for mechanosensitive channels, has previously been crystallized in the closed form, but not in the open form. Ensemble measurements and electrophysiological sieving experiments show that the open-diameter of the channel pore is >25 Å, but the exact size and whether the conformational change follows a helix-tilt or barrel-stave model are unclear. Here we report measurements of the distance changes on liposome-reconstituted MscL transmembrane α-helices, using a ‘virtual sorting’ single-molecule fluorescence energy transfer. We observed directly that the channel opens via the helix-tilt model and the open pore reaches 2.8 nm in diameter. In addition, based on the measurements, we developed a molecular dynamics model of the channel structure in the open state which confirms our direct observations.

Significance: Despite the increasing efforts in developing affinity grids to facilitate sample preparation for challenging systems and dynamic complexes, they are not widely used in cryo-electron microscopy (EM) owing to concerns of limiting resolution. We show that our affinity grids extract proteins through covalent bonding with 3.3-Å reconstruction. To our knowledge, no example of small proteins (<200 KDa) has been successfully tested with other affinity grids. With encouraging results further from a mixture sample, we believe that the strategy described here is highly applicable to a broad array of challenging macromolecules and thus is a method of broad interest to the cryo-EM community. The dramatic improvement in cryo-EM sample preparation outlined here paves the way to “purification on the grid.”