The Inhibitory Mechanism Of Human Prosaposin In SARS-CoV-2 Invasion

PurposeThe COVID-19 pandemic,caused by severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)infection,has had an unprecedented public health and economic impact on the world.In particular,a series of virus mutations in the process of virus transmission form a certain degree of immune escape for the body’s immune responses.S protein-related mutations affect the process of virus invasion into host cells,and then affect the pathogenicity of the virus.Since the outbreak of the virus,studies on the etiology and pathogenicity of the virus have been carried out.Antiviral strategies associated with COVID-19 treatment typically act at various points during the virus’s life cycle.Many researchers devote themselves to the study of antiviral strategies in the entry phase of the SARS-CoV-2,which mainly includes neutralizing antibodies and inhibitors in the virus fusion phase.The screening and discovery of receptors,host factors,or host restrictive factors related to the entry phase of SARSCoV-2 are also of concern.As the early stage of the whole life cycle of the virus,invasion is very important for the survival and reproduction of the virus in the later stage.Therefore,host genes that affect virus entry may be better targets in antiviral studies,which is of great significance for the antiviral treatment of SARS-CoV-2.MethodsResearch strategies are usually based on high-throughput screening.There are two main types of screening strategies based on gene manipulation:gain of function(GOF)and loss of function(LOF).The gain of function mainly includes cDNA library plasmid overexpression,CRISPR gene activation,and transposon gene activation.The loss of function mainly includes RNA interference(RNAi),and CRISPR-Cas9 gene knockout.At present,many studies screen related host factors based on gene knockout.Screening based on the cDNA overexpression library is restricted to the gene library which has similar biological function genes.Thus,wider coverage of the human genome has significant advantages.Here,we used a gain-offunction high-through screening method and obtained the candidate genes which may potentially affect the virus invasion.Further,we verified deeper molecular mechanisms with methods in immunology,cell biology,etc.ResultsOur screen results show that prosaposin(PSAP)may inhibit the invasion of SARS-CoV-2.Generally,PSAP protein plays a role in the regulation of lysosome function,and protects neuro and glial extracellularly.We showed that SARS-CoV-2 Spike protein binds specifically to PSAP through the RBD domain with a high affinity,and secreted PSAP can significantly inhibit the infection of SARS-CoV-2 pseudovirus and authentic virus.Then,we found that the PSAP protein promotes the release of the S1 subunit by interacting with the S protein,thus inhibiting the entry of the virus.Molecular docking simulation shows the spatial interaction between PSAP and S1 subunit.All interaction sites in the S1 subunit proteins are located outside the RBM region of the RBD domain.Therefore,we believe that the PSAP protein may have neutralizing antibody-like activity in the process of inhibiting the entry of SARSCoV-2.SignificantWe found that prosaposin can bind to the S protein of SARS-CoV-2 by exocytosis and inhibit the invasion of SARS-CoV-2 by promoting the S1 subunit release,elucidated the neutralizing antibody-like activity of nervous system-related host proteins firstly.Overall,PSAP can as a restriction factor of SARS-CoV-2 infection,offering new perspectives in the treatment of SARS-CoV-2 infection.