Altered hACE2 binding affinity and S1/S2 cleavage efficiency of SARS-CoV-2 spike protein mutants affect viral cell entry

SARS-CoV-2 variants are constantly emerging,hampering public health measures in controlling the number of infections.While it is well established that mutations in spike proteins observed for the different variants directly affect virus entry into host cells,there remains a need for further expansion of systematic and multifaceted comparisons.Here,we comprehensively studied the effect of spike protein mutations on spike expression and proteolytic activation,binding affinity,viral entry efficiency and host cell tropism of eight variants of concern(VOC)and variants of interest(VOI).We found that both the full-length spike and its receptor-binding domain(RBD)of Omicron bind to hACE2 with an affinity similar to that of the wild-type.In addition,Alpha,Beta,Delta and Lambda pseudoviruses gained significantly enhanced cell entry ability compared to the wild-type,while the Omicron pseudoviruses showed a slightly increased cell entry,suggesting the vastly increased rate of transmission observed for Omicron variant is not associated with its affinity to hACE2.We also found that the spikes of Omicron and Mu showed lower S1/S2 cleavage efficiency and inefficiently utilized TMPRSS2 to enter host cells than others,suggesting that they prefer the endocytosis pathway to enter host cells.Furthermore,all variants'pseudoviruses we tested gained the ability to enter the animal ACE2-expressing cells.Especially the infection potential of rats and mice showed significantly increased,strongly suggesting that rodents possibly become a reservoir for viral evolution.The insights gained from this study provide valuable guidance for a targeted approach to epidemic control,and contribute to a better understanding of SARS-CoV-2 evolution.

Cryo-EM snapshots of mycobacterial arabinosyltransferase complex EmbB2-AcpM2

Inhibition of Mycobacterium tuberculosis(Mtb)cell wall assembly is an established strategy for anti-TB chemotherapy.Arabinosyltransferase EmbB,which catalyzes the transfer of arabinose from the donor decaprenyl-phosphate-arabinose(DPA)to its arabinosyl acceptor is an essential enzyme for Mtb cell wall synthesis.Analysis of drug resistance mutations suggests that EmbB is the main target of the front-line anti-TB drug,ethambutol.Herein,we report the cryo-EM structures of Mycobacterium smegmatis EmbB in its"resting state"and DPA-bound"active state".EmbB is a fifteen-transmembrane-spanning protein,assembled as a dimer.Each protomer has an associated acyl-carrier-protein(AcpM)on their cytoplasmic surface.Confor-mational changes upon DPA binding indicate an asym-metric movement within the EmbB dimer during catalysis.Functional studies have identified critical residues in substrate recognition and catalysis,and demonstrated that ethambutol inhibits transferase activity of EmbB by competing with DPA.The structures represent the first step directed towards a rational approach for anti-TB drug discovery.