RESUMEN
OBJECTIVE To explore the protective mechanism of amifostine on acute radiation injury mice. METHODS Thirty C57BL/6J mice were randomly divided into normal control group， model group and amifostine group （150 mg/kg）， with 10 mice in each group. Thirty minutes before irradiation， the mice in the amifostine group were intraperitoneally injected with amifostine； normal control group and model group were given constant volume of normal saline intraperitoneally； then acute radiation injury was induced by 4 Gy X-ray radiation in both model group and amifostine group. The white blood cell count （WBC）， platelet count and red blood cell （RBC） count in mice were detected 2 hours before irradiation and on days 1， 4， 7， 10 and 14 after irradiation； the changes in the proportion of WBC （neutrophils， lymphocytes and monocytes） on the 7th day after irradiation were analyzed. The 16S rRNA high-throughput sequencing was used to analyze the structure of gut microbiota in mice feces on the 7th day after irradiation， then its correlation with WBC was analyzed. RESULTS The counts of WBC on the 1st， 4th， 7th and 10th day after irradiation， platelet count on the 10th day after irradiation and RBC count on the 1st day after irradiation in the amifostine group were significantly higher than those in model group （P＜0.05）. Compared with normal control group，β diversity of gut microbiome showed significant change， relative abundance of Firmicutes increased and that of Bacteroidetes decreased in model group. Amifostine could reverse the change in β diversity of gut microbiome， and the relative abundance of Bacteroidetes and Firmicutes. The model group consisted of four distinct species， namely Allobaculum， Erysipelotrichia， Erysipelotrichales and Erysipelotrichaceae， which were significantly negatively correlated with the proportion of peripheral blood lymphocytes （P＜0.01）； amifostine group consisted of two distinct species， namely Lactobacillus murinus and L. crispatus， which were significantly negatively correlated with the proportion of neutrophils （P＜0.05）. CONCLUSIONS Amifostine significantly improves irradiation-induced injury by regulating dysbiosis of LY201816） gut microbiota.
RESUMEN
The spike (S) protein of SARS-CoV-2 has been observed in three distinct pre-fusion conformations: locked, closed and open. Of these, the function of the locked conformation remains poorly understood. Here we engineered a SARS-CoV-2 S protein construct "S-R/x3" to arrest SARS-CoV-2 spikes in the locked conformation by a disulfide bond. Using this construct we determined high-resolution structures confirming that the x3 disulfide bond has the ability to stabilize the otherwise transient locked conformations. Structural analyses reveal that wild-type SARS-CoV-2 spike can adopt two distinct locked-1 and locked-2 conformations. For the D614G spike, based on which all variants of concern were evolved, only the locked-2 conformation was observed. Analysis of the structures suggests that rigidified domain D in the locked conformations interacts with the hinge to domain C and thereby restrains RBD movement. Structural change in domain D correlates with spike conformational change. We propose that the locked-1 and locked-2 conformations of S are present in the acidic high-lipid cellular compartments during virus assembly and egress. In this model, release of the virion into the neutral pH extracellular space would favour transition to the closed or open conformations. The dynamics of this transition can be altered by mutations that modulate domain D structure, as is the case for the D614G mutation, leading to changes in viral fitness. The S-R/x3 construct provides a tool for the further structural and functional characterization of the locked conformations of S, as well as how sequence changes might alter S assembly and regulation of receptor binding domain dynamics.
