Feline infectious peritonitis virus (FIPV) is an alphacoronavirus that causes a nearly 100% mortality rate without effective treatment. Here we report a 3.3-Å cryoelectron microscopy (cryo-EM) structure of the serotype I FIPV spike (S) protein, which is responsible for host recognition and viral entry. Mass spectrometry provided site-specific compositions of densely distributed high-mannose and complex-type N-glycans that account for 1/4 of the total molecular mass; most of the N-glycans could be visualized by cryo-EM. Specifically, the N-glycans that wedge between 2 galectin-like domains within the S1 subunit of FIPV S protein result in a unique propeller-like conformation, underscoring the importance of glycosylation in maintaining protein structures. The cleavage site within the S2 subunit responsible for activation also showed distinct structural features and glycosylation. These structural insights provide a blueprint for a better molecular understanding of the pathogenesis of FIP.cryoelectron microscopy | mass spectrometry | protein glycosylation | alphacoronavirus | feline infectious peritonitis virus C oronaviruses (CoVs) are enveloped viruses with single-

Thermally induced shape memory is an attractive feature of certain functional materials. Among the shape memory polymers, shape memory elastomers (SMEs) especially those with biodegradability have great potential in the biomedical field. In this study, we prepared waterborne biodegradable polyurethane SME based on poly(ε-caprolactone) (PCL) oligodiol and poly(l-lactic acid) (PLLA) oligodiol as the mixed soft segments. The ratio of the soft segments in polyurethanes was optimized for shape memory behavior. The thermally induced shape memory mechanism of the series of polyurethanes was clarified using differential scanning calorimeter (DSC), X-ray diffraction (XRD), and small-angle X-ray scattering (SAXS). In particular, the in situ SAXS measurements combined with shape deformation processes were employed to examine the stretch-induced (oriented) crystalline structure of the polyurethanes and to elucidate the unique mechanism for shape memory properties. The polyurethane with optimized PLLA crystalline segments showed a diamond-shape two-dimensional SAXS pattern after being stretched, which gave rise to better shape fixing and shape recovery. The shape memory behavior was further tested in 37 °C water. The biodegradable polyurethane comprising 38 wt % PCL segments and 25 wt % PLLA segments and synthesized at a relatively lower temperature by the waterborne procedure showed ∼100% shape recovery in 37 °C water. The biodegradable polyurethane SME also demonstrated good endothelial cell viability as well as low platelet adhesion/activation. We conclude that the waterborne biodegradable polyurethane SME possesses a unique thermally induced shape memory mechanism and may have potential applications in making shape memory biodegradable stents or scaffolds.

The surge of COVID-19 infection cases is spurred by emerging SARS-CoV-2 variants such as B.1.617. Here we report 38 cryo-EM structures, corresponding to the spike protein of the Beta (B.1.351), Gamma (P.1), Delta (B.1.617.2) and Kappa (B.1.617.1) variants in different functional states with and without its receptor, ACE2. Mutations on the N-terminal domain not only alter the conformation of the highly antigenic supersite of the Delta variant, but also remodel the glycan shield by deleting or adding N-glycans of the Delta and Gamma variants, respectively. Substantially enhanced ACE2 binding was observed for all variants, whose mutations on the receptor binding domain modulate the electrostatics of the binding interfaces. Despite their abilities to escape host immunity, all variants can be potently neutralized by three unique antibodies.