Mutations in the receptor-binding domain of human SARS CoV-2 spike protein increases its affinity to bind human ACE-2 receptor.

The severe acute respiratory syndrome virus-2 (SARS CoV-2) infection has resulted in the current global pandemic. The binding of SARS CoV-2 spike protein receptor-binding domain (RBD) to the human angiotensin converting enzyme-2 (ACE-2) receptor causes the host infection. The spike protein has undergone several mutations with reference to the initial strain isolated during December 2019 from Wuhan, China. A number of these mutant strains have been reported as variants of concern and as variants being monitored. Some of these mutants are known to be responsible for increased transmissibility of the virus. The reason for the increased transmissibility caused by the point mutations can be understood by studying the structural implications and inter-molecular interactions in the binding of viral spike protein RBD and human ACE-2. Here, we use the crystal structure of the RBD in complex with ACE-2 available in the public domain and analyse the 250 ns molecular dynamics (MD) simulations of wild-type and mutants; K417N, K417T, N440K, N501Y, L452R, T478K, E484K and S494P. The ionic, hydrophobic and hydrogen bond interactions, amino acid residue flexibility, binding energies and structural variations are characterized. The MD simulations provide clues to the molecular mechanisms of ACE-2 receptor binding in wild-type and mutant complexes. The mutant spike proteins RBD were associated with greater binding affinity with ACE-2 receptor. Communicated by Ramaswamy H. Sarma.

A case of reinfection with a different variant of SARS-CoV-2: case report.

Background: Coronavirus disease 2019 (COVID-19) was previously thought to have a low reinfection rate, but there are concerns that the reinfection rate will increase with the emergence and spread of mutant variants. This report describes the case of a 36-year-old, non-immunosuppressed man who was infected twice by two different variants of COVID-19 within a relatively short period. Case presentation: A 36-year-old Japanese man with no comorbidities was infected with the E484K variant (R.1 lineage) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Symptoms were mild and improved with symptomatic treatment alone. About four months later he presented to another outpatient department with high fever and headache. We diagnosed him as infected with the Alpha variant (B.1.1.7) of SARS-CoV-2 based on SARS-CoV-2 real-time reverse transcription polymerase chain reaction testing (RT-PCR). The patient was hospitalized with high fever. The patient received treatment in the form of anti-inflammatory therapy with corticosteroid and antibacterial chemotherapy. The patient improved without developing severe disease. Conclusion: Concerns have been raised that the reinfection rate of COVID-19 will increase with the emergence of mutant variants. Particularly in mild cases, adequate amounts of neutralizing antibodies may not be produced, and reinfection may thus occur. Continued attention to sufficient infection control is thus essential.

Impact of SARS-CoV-2 RBD Mutations on the Production of a Recombinant RBD Fusion Protein in Mammalian Cells.

SARS-CoV-2 receptor-binding domain (RBD) is a major target for the development of diagnostics, vaccines and therapeutics directed against COVID-19. Important efforts have been dedicated to the rapid and efficient production of recombinant RBD proteins for clinical and diagnostic applications. One of the main challenges is the ongoing emergence of SARS-CoV-2 variants that carry mutations within the RBD, resulting in the constant need to design and optimise the production of new recombinant protein variants. We describe here the impact of naturally occurring RBD mutations on the secretion of a recombinant Fc-tagged RBD protein expressed in HEK 293 cells. We show that mutation E484K of the B.1.351 variant interferes with the proper disulphide bond formation and folding of the recombinant protein, resulting in its retention into the endoplasmic reticulum (ER) and reduced protein secretion. Accumulation of the recombinant B.1.351 RBD-Fc fusion protein in the ER correlated with the upregulation of endogenous ER chaperones, suggestive of the unfolded protein response (UPR). Overexpression of the chaperone and protein disulphide isomerase PDIA2 further impaired protein secretion by altering disulphide bond formation and increasing ER retention. This work contributes to a better understanding of the challenges faced in producing mutant RBD proteins and can assist in the design of optimisation protocols.

DEVELOPMENT OF PCR TEST FOR DETECTION OF THE SARS-COV-2 GENETIC VARIANTS ALPHA, BETA, GAMMA, DELTA

The emergence of novel SARS-CoV-2 genetic variants with increased transmissivity and reduced antibody neutralization efficiency is a threat to global public health. Reverse transcription polymerase chain reaction (RT-PCR) with the use of fluorescent probes, which make it possible to detect the single nucleotide substitutions, is a technique suitable for screening the SARS-CoV-2 RNA-containing samples for the already known functionally significant mutations in the S-gene, identification of which allows to define and differentiate the most epidemiologically significant genetic variants. The study was aimed to develop an assay for the large-scale monitoring of the spread of the SARS-CoV-2 top-priority variants. Based on the whole-genome alignment of the SARS-CoV-2 sequences, deposited in the GISAID database, primers and LNA-modified probes were selected to detect mutations in the S gene, typical for the Alpha, Beta/Gamma and Delta variants of concern (VOC). The developed reagent kit for detection of the key mutations in the SARS-CoV-2 S gene by the real time RT-PCR has good analytical and diagnostic characteristics and was authorized as a medical device (reagent) for in vitro use. The results of detecting the VOC and the key mutations with the use of the developed reagent kit were consistent with the data of the whole genome sequencing of 1,500 SARS-CoV-2 RNA samples. The developed reagent kit and the subsequent SARS-CoV-2 RNA sequencing assay used to perform the epidemiological monitoring of SARS-CoV-2 variants made it possible to promptly report the emergence of the Delta genetic variant in Russia, and to trace the dynamic changes in the prevalence of Delta in Moscow Region in April-September 2021. © 2022 Obstetrics, Gynecology and Reproduction. All rights reserved.

The E484K Substitution in a SARS-CoV-2 Spike Protein Subunit Vaccine Resulted in Limited Cross-Reactive Neutralizing Antibody Responses in Mice.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), especially emerging variants, poses an increased threat to global public health. The significant reduction in neutralization activity against the variants such as B.1.351 in the serum of convalescent patients and vaccinated people calls for the design of new potent vaccines targeting the emerging variant. However, since most vaccines approved and in clinical trials are based on the sequence of the original SARS-CoV-2 strain, the immunogenicity and protective efficacy of vaccines based on the B.1.351 variant remain largely unknown. In this study, we evaluated the immunogenicity, induced neutralization activity, and protective efficacy of wild-type spike protein nanoparticle (S-2P) and mutant spike protein nanoparticle (S-4M-2P) carrying characteristic mutations of B.1.351 variant in mice. Although there was no significant difference in the induction of spike-specific IgG responses in S-2P- and S-4M-2P-immunized mice, neutralizing antibodies elicited by S-4M-2P exhibited noteworthy, narrower breadth of reactivity with SARS-CoV-2 variants compared with neutralizing antibodies elicited by S-2P. Furthermore, the decrease of induced neutralizing antibody breadth at least partly resulted from the amino acid substitution at position 484. Moreover, S-4M-2P vaccination conferred insufficient protection against live SARS-CoV-2 virus infection, while S-2P vaccination gave definite protection against SARS-CoV-2 challenge in mice. Together, our study provides direct evidence that the E484K substitution in a SARS-CoV-2 subunit protein vaccine limited the cross-reactive neutralizing antibody breadth in mice and, more importantly, draws attention to the unfavorable impact of this mutation in spike protein of SARS-CoV-2 variants on the induction of potent neutralizing antibody responses.

The effect of the E484K mutation of SARS-CoV-2 on the neutralizing activity of antibodies from BNT162b2 vaccinated individuals.

The reduced vaccine efficacy against the SARS-CoV-2 variant lineage B. 1.351 (beta variant) containing the E484K and N501Y mutations is well known. The E484K mutation in SARS-CoV-2 is thought to be responsible for weakened humoral immunity. Vaccine efficacy against the R.1 lineage, which contains the E484K mutation but not the N501Y mutation, is uncertain. Serum samples were collected from 100 healthy Japanese participants three weeks after receiving the second dose of the BNT162b2 vaccine, and serum neutralization antibody titers were measured against five SARS-CoV-2 variants. The geometric mean neutralization titers measured for the original and R.1 lineages were equivalent (91.90 ± 2.40 and 102.67 ± 2.28, respectively), whereas a low titer was measured for the beta variant (18.03 ± 1.92). Although further investigations with other variant strains and serum samples are essential, our results imply that the weakened humoral response is not caused solely by the E484K mutation. (UMIN000043340).

A screening strategy for identifying the dominant variant of SARS-COV-2 in the fifth peak of Kurdistan- Iran population using HRM and Probe-based RT-PCR assay.

By the emergence of SARS CoV-2 variants, many studies were developed to deal with it. The high transmissibility and mortality rate of some variants, in particular developing countries have caused the operation of simple diagnostic tests for genomic surveillance. In this study, we developed two assays of High Resolution Melting (HRM) and Probe-based RT-PCR as simple and inexpensive methods to identify the variants. We screened the mutations of del69-70, E484K, E484Q, D614G, L452R, and T478K in 100 cases from SARS-COV-2 positive patients in Kurdistan- Iran population. In general, the result of the two methods overlapped each other, nevertheless, we suggested HRM results be confirmed with a standard assay (Whole-Genome Sequencing). This work indicated that HRM as the rapid and inexpensive method could identify and categorize the variants of SARS CoV-2 and reduce the costs for carrying out sequencing.

Emergency SARS-CoV-2 Variants of Concern: Novel Multiplex Real-Time RT-PCR Assay for Rapid Detection and Surveillance.

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread worldwide. Many variants of SARS-CoV-2 have been reported, some of which have increased transmissibility and/or reduced susceptibility to vaccines. There is an urgent need for variant phenotyping for epidemiological surveillance of circulating lineages. Whole-genome sequencing is the gold standard for identifying SARS-CoV-2 variants, which constitutes a major bottleneck in developing countries. Methodological simplification could increase epidemiological surveillance feasibility and efficiency. We designed a novel multiplex real-time reverse transcriptase PCR (RT-PCR) to detect SARS-CoV-2 variants with S gene mutations. This multiplex PCR typing method was established to detect 9 mutations with specific primers and probes (ΔHV 69/70, K417T, K417N, L452R, E484K, E484Q, N501Y, P681H, and P681R) against the receptor-binding domain of the spike protein of SARS-CoV-2 variants. In silico analyses showed high specificity of the assays. Variants of concern (VOC) typing results were found to be highly specific for our intended targets, with no cross-reactivity observed with other upper respiratory viruses. The PCR-based typing methods were further validated using whole-genome sequencing and a commercial kit that was applied to clinical samples of 250 COVID-19 patients from Taiwan. The screening of these samples allowed the identification of epidemic trends by time intervals, including B.1.617.2 in the third Taiwan wave outbreak. This PCR typing strategy allowed the detection of five major variants of concern and also provided an open-source PCR assay which could rapidly be deployed in laboratories around the world to enhance surveillance for the local emergence and spread of B.1.1.7, B.1.351, P.1, and B.1.617.2 variants and of four Omicron mutations on the spike protein (ΔHV 69/70, K417N, N501Y, P681H). IMPORTANCE COVID-19 has spread globally. SARS-CoV-2 variants of concern (VOCs) are leading the next waves of the COVID-19 pandemic. Previous studies have pointed out that these VOCs may have increased infectivity, have reduced vaccine susceptibility, change treatment regimens, and increase the difficulty of epidemic prevention policy. Understanding SARS-CoV-2 variants remains an issue of concern for all local government authorities and is critical for establishing and implementing effective public health measures. A novel SARS-CoV-2 variant identification method based on a multiplex real-time RT-PCR was developed in this study. Five SARS-CoV-2 variants (Alpha, Beta, Gamma, Delta, and Omicron) were identified simultaneously using this method. PCR typing can provide rapid testing results with lower cost and higher feasibility, which is well within the capacity for any diagnostic laboratory. Characterizing these variants and their mutations is important for tracking SAR-CoV-2 evolution and is conducive to public infection control and policy formulation strategies.

Association of E484K Spike Protein Mutation With Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infection in Vaccinated Persons: Maryland, January-May 2021.

Among 9048 people infected with SARS-CoV-2 between January and May 2021 in Maryland, in regression-adjusted analysis, SARS-CoV-2 viruses carrying the spike protein mutation E484K were disproportionately prevalent among persons infected after full vaccination against COVID-19 compared with infected persons who were not fully vaccinated (aOR, 1.96; 95% CI: 1.36-2.83).

Emergence of the E484K Mutation in Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Lineage B.1.1.345 in Upstate New York.

A severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) B.1.1.345 variant carrying the E484K mutation was detected in 4 patients with no apparent epidemiological association from a hospital network in upstate New York. Subsequent analysis identified an additional 11 B.1.1.345 variants from this region between December 2020 and February 2021.

SARS-CoV-2 E484K Mutation Narrative Review: Epidemiology, Immune Escape, Clinical Implications, and Future Considerations.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spread rapidly over the world and claimed million lives. The virus evolves constantly, and a swarm of mutants is a now major concern globally. Distinct variants could have independently converged on same mutation, despite being detected in different geographic regions, which suggested it could confer an evolutionary advantage. E484K has rapidly emerged and has frequently been detected in several SARS-CoV-2 variants of concern. In this study, we review the epidemiology and impact of E484K, its effects on neutralizing effect of several monoclonal antibodies, convalescent plasma, and post-vaccine sera.

Key Substitutions in the Spike Protein of SARS-CoV-2 Variants Can Predict Resistance to Monoclonal Antibodies, but Other Substitutions Can Modify the Effects.

Mutations in the spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants can compromise the effectiveness of therapeutic antibodies. Most clinical-stage therapeutic antibodies target the spike receptor binding domain (RBD), but variants often have multiple mutations in several spike regions. To help predict antibody potency against emerging variants, we evaluated 25 clinical-stage therapeutic antibodies for neutralization activity against 60 pseudoviruses bearing spikes with single or multiple substitutions in several spike domains, including the full set of substitutions in B.1.1.7 (alpha), B.1.351 (beta), P.1 (gamma), B.1.429 (epsilon), B.1.526 (iota), A.23.1, and R.1 variants. We found that 14 of 15 single antibodies were vulnerable to at least one RBD substitution, but most combination and polyclonal therapeutic antibodies remained potent. Key substitutions in variants with multiple spike substitutions predicted resistance, but the degree of resistance could be modified in unpredictable ways by other spike substitutions that may reside outside the RBD. These findings highlight the importance of assessing antibody potency in the context of all substitutions in a variant and show that epistatic interactions in spike can modify virus susceptibility to therapeutic antibodies. IMPORTANCE Therapeutic antibodies are effective in preventing severe disease from SARS-CoV-2 infection (COVID-19), but their effectiveness may be reduced by virus variants with mutations affecting the spike protein. To help predict resistance to therapeutic antibodies in emerging variants, we profiled resistance patterns of 25 antibody products in late stages of clinical development against a large panel of variants that include single and multiple substitutions found in the spike protein. We found that the presence of a key substitution in variants with multiple spike substitutions can predict resistance against a variant but that other substitutions can affect the degree of resistance in unpredictable ways. These findings highlight complex interactions among substitutions in the spike protein affecting virus neutralization and, potentially, virus entry into cells.

Reduced levels of convalescent neutralizing antibodies against SARS-CoV-2 B.1+L249S+E484K lineage.

The E484K mutation at the SARS-CoV-2 Spike protein emerged independently in different variants around the world and has been widely associated with immune escape from neutralizing antibodies generated during previous infection or vaccination. In this work, the B.1 + L249S+E484K lineage was isolated along with A.1, B.1.420, and B.1.111 SARS-CoV-2 lineages without the E484K mutation and the neutralizing titer of convalescent sera was compared using microneutralization assays. While no significant differences in the neutralizing antibody titers were found between A.1 and B.lineages without the E484K mutation, the neutralizing titers against B.1 + L249S+E484K were 1.5, 1.9, 2.1, and 1.3-fold lower than against A.1, B.1.420, B.1.111-I, and B.1.111-II, respectively. However, molecular epidemiological data indicate that there is no increase in the transmissibility rate associated with this new lineage. This study supports the capability of new variants with the E484K mutation to be resistant to neutralization by humoral immunity, and therefore the need to intensify surveillance programs to determine if these lineages represent a risk for public health.

Neutralisation of the SARS-CoV-2 Delta variant sub-lineages AY.4.2 and B.1.617.2 with the mutation E484K by Comirnaty (BNT162b2 mRNA) vaccine-elicited sera, Denmark, 1 to 26 November 2021.

Several factors may account for the recent increased spread of the SARS-CoV-2 Delta sub-lineage AY.4.2 in the United Kingdom, Romania, Poland, and Denmark. We evaluated the sensitivity of AY.4.2 to neutralisation by sera from 30 Comirnaty (BNT162b2 mRNA) vaccine recipients in Denmark in November 2021. AY.4.2 neutralisation was comparable to other circulating Delta lineages or sub-lineages. Conversely, the less prevalent B.1.617.2 with E484K showed a significant more than 4-fold reduction in neutralisation that warrants surveillance of strains with the acquired E484K mutation.

Emergence of SARS-CoV-2 Variant B.1.575.2, Containing the E484K Mutation in the Spike Protein, in Pamplona, Spain, May to June 2021.

With the emergence of new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants and the acquisition of novel mutations in existing lineages, the need to implement methods capable of monitoring viral dynamics arises. We report the emergence and spread of a new SARS-CoV-2 variant within the B.1.575 lineage, containing the E484K mutation in the spike protein (named B.1.575.2), in a region in northern Spain in May and June 2021. SARS-CoV-2-positive samples with cycle threshold values of ≤30 were selected to screen for presumptive variants using the TaqPath coronavirus disease 2019 (COVID-19) reverse transcription (RT)-PCR kit and the TaqMan SARS-CoV-2 mutation panel. Confirmation of variants was performed by whole-genome sequencing. Of the 200 samples belonging to the B.1.575 lineage, 194 (97%) corresponded to the B.1.575.2 sublineage, which was related to the presence of the E484K mutation. Of 197 cases registered in the Global Initiative on Sharing Avian Influenza Data (GISAID) EpiCoV database as lineage B.1.575.2, 194 (99.5%) were identified in Pamplona, Spain. This report emphasizes the importance of complementing surveillance of SARS-CoV-2 with sequencing for the rapid control of emerging viral variants.

Functional Effects of Receptor-Binding Domain Mutations of SARS-CoV-2 B.1.351 and P.1 Variants.

The recent identification and rise to dominance of the P.1 and B.1.351 SARS-CoV-2 variants have brought international concern because they may confer fitness advantages. The same three positions in the receptor-binding domain (RBD) are affected in both variants, but where the 417 substitution differs, the E484K/N501Y have co-evolved by convergent evolution. Here we characterize the functional and immune evasive consequences of the P.1 and B.1.351 RBD mutations. E484K and N501Y result in gain-of-function with two different outcomes: The N501Y confers a ten-fold affinity increase towards ACE-2, but a modest antibody evasion potential of plasma from convalescent or vaccinated individuals, whereas the E484K displays a significant antibody evasion capacity without a major impact on affinity. On the other hand, the two different 417 substitutions severely impair the RBD/ACE-2 affinity, but in the combined P.1 and B.1.351 RBD variants, this effect is partly counterbalanced by the effect of the E484K and N501Y. Our results suggest that the combination of these three mutations is a two-step forward and one step back in terms of viral fitness.

Sensitivity of two SARS-CoV-2 variants with spike protein mutations to neutralising antibodies.

SARS-CoV-2 infections elicit a humoral immune response capable of neutralising the virus. However, multiple variants have emerged with mutations in the spike protein amongst others, the key target of neutralising antibodies. We evaluated the neutralising efficacy of 89 serum samples from patients, infected with SARS-CoV-2 in the beginning of 2020, against two virus variants isolated from acutely infected patients and harbouring spike protein mutations. One isolate was assigned to lineage B.1.351 (MUC-IMB-B.1.351) whilst the other (MUC-484) was isolated from an immunocompromised patient, sharing some but not all mutations with B.1.351 and representing a transitional variant. Both variants showed a significant reduction in neutralisation sensitivity compared to wild-type SARS-CoV-2 with MUC-IMB-B.1.351 being almost completely resistant to neutralisation. The observed reduction in neutralising activity of wild-type-specific antibodies against both variants suggests that individual mutations in the spike protein are sufficient to confer a potent escape from the humoral immune response. In addition, the effect of escape mutations seems to accumulate, so that more heavily mutated variants show a greater loss of sensitivity to neutralisation up to complete insensitivity as observed for MUC-IMB-B.1.351. From a clinical point of view, this might affect the efficacy of (monoclonal) antibody treatment of patients with prolonged infections as well as patients infected with variants other than the donor. At the same, this could also negatively influence the efficacy of current vaccines (as they are based on wild-type spike protein) emphasising the need to thoroughly surveil the emergence and distribution of variants and adapt vaccines and therapeutics accordingly.

Exploring the immune evasion of SARS-CoV-2 variant harboring E484K by molecular dynamics simulations.

Although the current coronavirus disease 2019 (COVID-19) vaccines have been used worldwide to halt spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the emergence of new SARS-CoV-2 variants with E484K mutation shows significant resistance to the neutralization of vaccine sera. To better understand the resistant mechanism, we calculated the binding affinities of 26 antibodies to wild-type (WT) spike protein and to the protein harboring E484K mutation, respectively. The results showed that most antibodies (~85%) have weaker binding affinities to the E484K mutated spike protein than to the WT, indicating the high risk of immune evasion of the mutated virus from most of current antibodies. Binding free energy decomposition revealed that the residue E484 forms attraction with most antibodies, while the K484 has repulsion from most antibodies, which should be the main reason of the weaker binding affinities of E484K mutant to most antibodies. Impressively, a monoclonal antibody (mAb) combination was found to have much stronger binding affinity with E484K mutant than WT, which may work well against the mutated virus. Based on binding free energy decomposition, we predicted that the mutation of four more residues on receptor-binding domain (RBD) of spike protein, viz., F490, V483, G485 and S494, may have high risk of immune evasion, which we should pay close attention on during the development of new mAb therapeutics.

A Simple Reverse Transcriptase PCR Melting-Temperature Assay To Rapidly Screen for Widely Circulating SARS-CoV-2 Variants.

The increased transmission of SARS-CoV-2 variants of concern (VOC), which originated in the United Kingdom (B.1.1.7/alpha), South Africa (B1.351/beta), Brazil (P.1/gamma), the United States (B.1.427/429 or epsilon), and India (B.1.617.2/delta), requires a vigorous public health response, including real-time strain surveillance on a global scale. Although genome sequencing is the gold standard for identifying these VOCs, it is time-consuming and expensive. Here, we describe a simple, rapid, and high-throughput reverse transcriptase PCR (RT-PCR) melting-temperature (Tm) screening assay that identifies the first three major VOCs. RT-PCR primers and four sloppy molecular beacon (SMB) probes were designed to amplify and detect the SARS-CoV-2 N501Y (A23063T) and E484K (G23012A) mutations and their corresponding wild-type sequences. After RT-PCR, the VOCs were identified by a characteristic Tm of each SMB. Assay optimization and testing was performed with RNA from SARS-CoV-2 USA WA1/2020 (wild type [WT]), B.1.1.7, and B.1.351 variant strains. The assay was then validated using clinical samples. The limit of detection for both the WT and variants was 4 and 10 genomic copies/reaction for the 501- and 484-codon assays, respectively. The assay was 100% sensitive and 100% specific for identifying the N501Y and E484K mutations in cultured virus and in clinical samples, as confirmed by Sanger sequencing. We have developed an RT-PCR melt screening test for the major VOCs that can be used to rapidly screen large numbers of patient samples, providing an early warning for the emergence of these variants and a simple way to track their spread.

E484K mutation in SARS-CoV-2 RBD enhances binding affinity with hACE2 but reduces interactions with neutralizing antibodies and nanobodies: Binding free energy calculation studies.

The pandemic of the COVID-19 disease caused by SARS-CoV-2 has led to more than 200 million infections and over 4 million deaths worldwide. The progress in the developments of effective vaccines and neutralizing antibody therapeutics brings hopes to eliminate the threat of COVID-19. However, SARS-CoV-2 continues to mutate, and several new variants have been emerged. Among the various naturally-occurring mutations, the E484K mutation shared by many variants attracted serious concerns, which may potentially enhance the receptor binding affinity and reduce the immune response. In the present study, the molecular mechanism behind the impacts of E484K mutation on the binding affinity of the receptor-binding domain (RBD) with the receptor human angiotensin-converting enzyme 2 (hACE2) was investigated by using the molecular dynamics (MD) simulations combined with the molecular mechanics-generalized Born surface area (MMGBSA) method. Our results indicate that the E484K mutation results in more favorable electrostatic interactions compensating the burial of the charged and polar groups upon the binding of RBD with hACE2, which significantly improves the RBD-hACE2 binding affinity. Besides that, the E484K mutation also causes the conformational rearrangements of the loop region containing the mutant residue, which leads to tighter binding interface of RBD with hACE2 and formation of some new hydrogen bonds. The tighter binding interface and the new hydrogen bonds formation also contribute to the improved binding affinity of RBD to the receptor hACE2. In addition, six neutralizing antibodies and nanobodies complexed with RBD were selected to explore the effects of E484K mutation on the recognition of these antibodies to RBD. The simulation results show that the E484K mutation significantly reduces the binding affinities to RBD for most of the studied neutralizing antibodies/nanobodies, and the decrease in the binding affinities is mainly owing to the unfavorable electrostatic interactions caused by the mutation. Our studies revealed that the E484K mutation may improve the binding affinity between RBD and the receptor hACE2, implying more transmissibility of the E484K-containing variants, and weaken the binding affinities between RBD and the studied neutralizing antibodies/nanobodies, indicating reduced effectiveness of these antibodies/nanobodies. Our results provide valuable information for the effective vaccine development and antibody/nanobody drug design.