ABSTRACT
The COVID-19 epidemic is raging around the world, including the emergence of viral mutant strains such as Delta and Omicron, posing severe challenges to people's health and quality of life. Full understanding life cycle of the virus in host cells helps to reveal inactivation mechanism of antibody and provide inspiration for the development of a new-generation vaccines. In this work, molecular recognitions and conformational changes of SARS-CoV-2 spike protein (SP) mutants (i.e., Delta, Mu and Omicron) and three essential partners (i.e., membrane receptor hACE2, protease TMPRSS2 and antibody C121) both were compared and analyzed using molecular simulations. Water basin and binding free energy calculations both show that the three mutants possess higher affinity for hACE2 than WT, exhibiting stronger virus transmission. The descending order of cleavage ability by TMPRSS2 is Mu, Delta, Omicron and WT, which is related to the new S1/S2 cutting site induced by transposition effect. The inefficient utilization of TMPRSS2 by Omicron is consistent with its primary entry into cells via the endosomal pathway. In addition, RBD-directed antibody C121 showed obvious resistance to Omicron, which may have originated from high fluctuation of approaching angles, high flexibility of I472-F490 loop and reduced binding ability. According to the overall characteristics of the three mutants, high infectivity, high immune escape and low virulence may be the future evolutionary selection of SARS-CoV-2. In a word, this work not only proposes the possible resistance mechanism of SARS-CoV-2 mutants, but also provides theoretical guidance for the subsequent drug design against COVID-19 based on SP structure.