The side chain of Arginine can form an additional hydrogen bond interaction with RBD, which enhances the affinity of 20G6 with RBD and potentially contributes to the stronger competitive ability against ACE2. through a novel sheet interaction. It is found that the S375F mutation on Omicron RBD disrupts the structure of strand, thus impair the binding with 20G6. The study demonstrates that sharkderived vnarbodies offer a prophylactic and therapeutic option against most SARSCoV2 variants and provide insights into antibody evasion by the Omicron variant. Keywords:neutralization, receptor binding domain (RBD), SARSCoV2, variants of concerns (VOCs) Sharkderived vnarbodies 20G6 and 17F6 broadly neutralize SARSCoV2 Wuhan, Alpha, Beta, Kappa, Delta, Deltaplus, Lambda variants, and sarbecovirus coronaviruses, but are unexpectedly ineffective for Omicron. Intranasal administration of 20G6 confers effective preventive and therapeutic effects in mice infected with SARSCoV2 Wuhan and Beta variant. Structural analysis elucidates the neutralizing mechanism and revealed the S375F mutation on Omicron receptor binding domain renders the evasion of neutralization by 20G6like antibodies. == 1. Introduction == Since the outbreak of the COVID19 pandemic in December 2019,[1,2]about 5 billion people have been infected and more than 6 million deaths have been reported to World Health Organization as of April 9, 2022. Many SARSCoV2 variants appeared under selective pressure from host immunity with high infectivity and immune evasion, such as the Alpha (B.1.1.7),[3,4]Beta (B.1.351),[5]Delta (B.1.617.2),[6]Gamma (P.1)[7]and Omicron (B.1.1.529).[8]These variants brought considerable challenges to the prevention BCR-ABL-IN-1 and treatment of SARSCoV2 infections. Effective and affordable preventive and therapeutic strategies are urgently needed. Understanding mechanisms of virus neutralization and the escape will expedite our effort in virus prevention and therapy. In addition to the active immunity brought by vaccination, the passive immunity of neutralizing antibodies can play an important role in preventing and treating infectious diseases. The BCR-ABL-IN-1 vaccine’s protective effect is greatly reduced in people with weakened immune systems, such as elderly and people with immunecompromised conditions. In this case, the role of passive immunity is significant. The convalescent serum has been used to treat COVID19 patients with a considerable effect but is limited by the scarcity of sources and possible side effects.[9,10] Like other coronaviruses, SARSCoV2 entry into host cells is mediated by the homotrimeric spike (S) glycoprotein.[11]The spike is composed of two subunits, S1 and S2. S1 binds the host cell receptor angiotensinconverting enzyme 2 (ACE2) by the receptorbinding domain (RBD),[12,13]which serves as the primary target for neutralizing antibodies. S2 is responsible for fusing the virus with cellular membranes.[14]Many humanderived SARSCoV2 neutralizing antibodies targeting S protein have been identified and developed, some of which have entered clinical trials.[15]However, the high production costs, large doses needed, and lowtemperature requirements for transportation and storage make it challenging to apply on a large scale costeffectively. Singledomain antibodies or adjustable site from the weighty string of HACbs (VHH) from camelids, creating a smaller sized molecular BCR-ABL-IN-1 pounds (15 kD) than human being antibodies (150 kD), are termed nanobodies commonly.[16,17]Nanobodies show great potential in biomedical applications, including tumor, disease, autoimmune disease, swelling, and other illnesses.[18,19,20,21]The first nanobodybased medicine was approved to take care of acquired thrombotic thrombocytopenic purpura (aTTP) in 2018.[22]Another class of singledomain antibodies, namely adjustable fresh antigen receptor (VNAR), creating a smaller sized molecular weight of 13 kD, was within cartilaginous fish such as for example sharks, skates, and rays.[23]Singledomain antibodies possess advantages such as for example high affinity to focus on CEACAM8 proteins, better thermal stability, little molecular weight, and low production cost in nonmammalian expression systems. Among the benefits of singledomain antibodies can be they can bind to epitopes that aren’t reachable by traditional human being antibodies for their smaller sized size and framework. Several camelidderived nanobodies against the RBD area from the SARSCoV2 Spike (S) proteins have already been reported lately.[24,25,26,27]We took a different strategy by searching sharkderived solitary site antibodies, VNAR, which we termed it as vnarbodies to tell apart from camelderived nanobodies, for neutralizing SARSCoV2. Since shark bloodstream and body liquids contain high focus of urea (about 350 103m),[28]sharkderived vnarbodies might possess better physiochemical balance than humanderived antibodies. We immunized sharks with SARSCoV2 Spike proteins and constructed a phage bamboo.