Serine protease inhibitors LmSPN2 and LmSPN3 co-regulate embryonic diapause in Locusta migratoria manilensis(Meyen)via the Toll pathway

Female adults of the migratory locust,Locusta migratoria manilensis(Meyen),can sense seasonal photoperiod changes,which induces embryonic diapause as a key strategy to overwinter.Serine protease inhibitor genes(SPNs)were thought to play key roles during diapause,while few SPNs were functionally characterized.LmSPN2 was one of those genes differentially expressed between diapause and non-diapause eggs;however,its biological function remained to be explored.So,we conducted RNAi knockdown of LmSPN2,resulting in a significant decrease of the egg diapause rate by 29.7%.Using yeast two-hybrid assays,co-immunoprecipitation,and pull-down methods,we found an interaction between LmSPN2 and LmSPN3,which was proved to be mediated by a glutamate(E331)binding site of LmSPN2.RNAi knockdown of LmSPN3 resulted in a significant increase in diapause rate by 14.6%,indicating an inverse function of LmSPN2 and LmSPN3 on diapause regulation.Double knockdown of two SPN genes resulted in a 26.4%reduction in diapause rate,indicating that LmSPN2 was the dominant regulatory signal.Moreover,we found four Toll pathway genes(easter,spätzle,pelle,and dorsal)upregulated significantly after the knockdown of LmSPN2 while downregulated after the knockdown of LmSPN3.Therefore,we speculate that two SPNs regulate diapause through the Toll pathway.Our results indicated that LmSPN2 positively regulates locust egg entry into diapause,while LmSPN3 is a negative regulator of embryonic commitment to diapause.Their interaction is mediated by the binding site of E331 and influences egg diapause through the Toll pathway.This mechanistic understanding of diapause regulation expands our understanding of insect developmental regulation and provides functional targets for developing locust management strategies.

Potato protease inhibitors,a functional food material with antioxidant and anticancer potential

Potato protease inhibitors(PPIs),as the main component of potato protein isolate,have good safety,nutrition and great market potential.The antioxidant and anticancer properties of PPIs were evaluated with cellbased biological assays.The results showed that when the concentration of PPIs was 5 mg/mL,the peroxyl radical scavenging value was(2119±204)mg VCE/100 g,and the cellular antioxidant activity values were(45.83±3.5)(no PBS wash)and(33.25±4.4)μmol QE/100 g(PBS wash).Cells pretreated with PPIs could significantly prevent the oxidative damage induced by H_(2)O_(2),inhibit the morphological changes of cells and maintain the integrity.Furthermore,PPIs had selective anti-proliferative effects on GIST882 cells(IC50=(10.53±3.87)mg/mL)and demonstrated potent inhibition of the growth,migration and invasion of cancer cells.These findings provide a scientific basis for PPIs as promising candidates for functional foods to aid in the prevention of oxidative damage and cancer.

Purification and Biochemical Characterization of a Protease Inhibitor Ⅱ Family from Jalapeno Pepper(Capsicum annuum L.)

Capsicum annuum L. was initially domesticated in Mexico and northern Central America, and represented an ancient Neotropical plant food complex. The purpose of this paper is to report the isolation and purification of a novo-member of a protease inhibitor from jalape&ntildeo pepper (Capsicum annuum L.) (PIJP). The molecular weight of PIJP inhibitor is 5.95 kDa with 56 amino acids and 6 Cys residues with high inhibitory activity to trypsin with a Ki value of 95 nM. This inhibitor according to the alignment with homologous from NCBI and Pfam databases is a member of proteinase inhibitors II. It is worthwhile to mention a major compositional difference between the proteinase inhibitor II families which have 8 Cys residues. PIJP is the first purified proteinase inhibitor, member of this family with only 6 Cys residues.

Comparative Study on the Protease Inhibitors from Fish Eggs

The protease inhibitor was purified from five different fish eggs. The molecular weights of Pacific herring, chum salmon, pond smelt, glassfish, and Alaska pollock egg protease inhibitors were 120, 89, 84.5, 17, and 16.8kDa, respectively. The specific inhibitory activity of glassfish egg protease inhibitor was the highest followed by those of Pacific herring and Alaska pollock in order. The specific inhibitory activity and purity of glassfish egg protease inhibitor were 19.70 U mg^- 1 protein and 164.70 folds of purification, respectively. Glassfish egg protease inhibitor was reasonably stable at 50 - 65℃ and pH 8, which was more stable at high temperature and pH than protease inhibitors from the other fish species. Glassfish egg protease inhibitor was noncompetitive with inhibitor constant （Ki） of 4.44 nmol L^-1

Association between calcium sensing receptor gene polymorphisms and chronic pancreatitis in a US population:Role of serine protease inhibitor Kazal 1type and alcohol

AIM： To test the hypothesis that calcium sensing receptor （CASR） polymorphisms are associated with chronic pancreatitis （CP）, and to determine whether serine protease inhibitor Kazal 1type （SPINK1） N34S or alcohol are necessary co-factors in its etiology. METHODS： Initially, 115 subjects with pancreatitis and 66 controls were evaluated, of whom 57 patients and 21 controls were predetermined to carry the high-risk SPINK1 N34S polymorphism. We sequenced CASR gene exons 2, 3, 4, 5 and 7, areas containing the majority of reported polymorphisms and novel mutations. Based on the initial results, we added 223 patients and 239 controls to analyze three common nonsynonymous single nucleotide polymorphisms （SNPs） in exon 7 （A986S, R990G, and Q1011E）. RESULTS： The CASR exon 7 R990G polyrnorphism was significantly associated with CP （OR, 2.01; 95% CI, 1.12-3.59; P = 0.015）. The association between CASR R990G and CP was stronger in subjects who reported moderate or heavy alcohol consumption （OR, 3.12; 95% CI, 1.14-9.13; P = 0.018）. There was no association between the various CASR genotypes and SPINK1 N34S in pancreatitis. None of the novel CASR polymorphisms reported from Germany and India was detected. CONCLUSION： Our United States-based study confirmed an association of CASR and CP and for the first time demonstrated that CASR R990G is a significant risk factor for CP. We also conclude that the risk of CP with CASR R990G is increased in subjects with moderate to heavy alcohol consumption.

NS3 protease inhibitors for treatment of chronic hepatitis C: Efficacy and safety

A new treatment paradigm for hepatitis C is that the treatment must include an existing direct-acting antiviral agent, namely, a protease inhibitor(PI) combined with PEGylated interferon-a and ribavirin. The currently mar-keted PIs and PIs in clinical trials have different mecha-nisms of action. The development of new PIs aims for an improved safety profile and higher effectiveness. This article reviews NS3/4A protease inhibitors, focusing on major criteria such as their effectiveness and safety. Specific attention is paid to dosing regimens and adverse event profiles of PIs administered in clinical settings.

Molecular mechanism of modulating the liquefaction epididymal protease inhibitor of human semen

Aim： To study the molecular mechanism of epididymal protease inhibitor （Eppin） modulating the process of prostate specific antigen （PSA） digesting semenogelin （Sg）. Methods： Human Sg cDNA （nucleotides 82-849） and Eppin cDNA （nucleotides 70-423） were generated by polymerase chain reaction （PCR） and cloned into pET-100D/TOPO. Recombinant Eppin and Sg （rEppin and rSg） were produced by BL21 （DE3）. The association of Eppin with Sg was studied by far-western immunoblot and radioautography. In vitro the digestion of rSg by PSA in the presence or absence of rEppin was studied. The effect of anti-Q20E （N-terminal） and C-terminal of Eppin on Eppin-Sg binding was monitored. Results： Eppin binds Sg on the surface of human spermatozoa with the C-terminal of Eppin （amino acids 75-133）. rSg was digested with PSA and many low molecular weight fragments were produced. When rEppin is bound to rSg, then digested by PSA, incomplete digestion and a 15-kDa fragment results. Antibody binding to the N-terminal of rEppin did not affect rSg digestion. Addition of antibodies to the C-terminal of rEppin inhibited the modulating effect of rEppin. Conclusion： Eppin protects a 15-kDa fragment of rSg from hydrolysis by PSA.

Molecular mechanism of epididymal protease inhibitor modulating the liquafication of human semen

To study the molecular mechanism of epididymal protease inhibitor （Eppin） modulating the liquafication of semen. Methods： Human semenogelin cDNA （nucleotides 82-849） and Eppin cDNA （nucleotides 70-423） were generated by PCR and cloned into pET-100D/TOPO.Recombinant Eppin and Sg were produced by BL21 （DE3）. The association of Eppin with Sg was studied by far-western and radioautography.In vitro the digestion of Sg by PSA in the presence or absence of recombinant Eppin was studied. The effect of anti-Q20E （N-terminal） and C-terminal of Eppin on Eppin-Sg binding was monitored. Results： Eppin binds Sg on the surface of human spermatozoa with C-terminal Eppin （aa75-133）.Recombinant Sg was digested with PSA ,many low molecular weight fragments were produced, when Eppin is bound to Sg ,then digested by PSA ,producing incomplete digestion and a 14.5-14.8 kDa fragmen. Antibody binding to the N-terminal of Eppin did not affect Sg digestion. Addition of antibodies to the C-terminal of Eppin inhibited the modulating effects of Eppin. Conclusion： Eppin modulates the digestion activity of PSA through binding Sg.The active site locates at C-terminal.

Effectiveness and safety of first-generation protease inhibitors in clinical practice:Hepatitis C virus patients with advanced fibrosis

AIM:To evaluates the effectiveness and safety of the first generation,NS3/4A protease inhibitors(PIs) in clinical practice against chronic C virus,especially in patients with advanced fibrosis. METHODS:Prospective study and non-experimental analysis of a multicentre cohort of 38 Spanish hospitals that includes patients with chronic hepatitis C genotype 1,treatment-na?ve(TN) or treatment-experienced(TE),who underwent triple therapy with the first generation NS3/4A protease inhibitors,boceprevir(BOC) and telaprevir(TVR),in combination with pegylated interferon and ribavirin. The patients were treatment in routine practice settings. Data on the study population and on adverse clinical and virologic effects were compiled during the treatment period and during follow up.RESULTS:One thousand and fifty seven patients were included,405(38%) were treated with BOC and 652(62%) with TVR. Of this total,30%(n = 319) were TN and the remaining were TE:28%(n = 298) relapsers,12%(n = 123) partial responders(PR),25%(n = 260) null-responders(NR) and for 5%(n = 57) with prior response unknown. The rate of sustained virologic response(SVR) by intention-to-treatment(ITT) was greater in those treated with TVR(65%) than in those treated with BOC(52%)(P < 0.0001),whereas by modified intention-to-treatment(m ITT) no were found significant differences. By degree of fibrosis,56% of patients were F4 and the highest SVR rates were recorded in the non-F4 patients,both TN and TE. In the analysis by groups,the TN patients treated with TVR by ITT showed a higher SVR(P = 0.005). However,by m ITT there were no significant differences between BOC and TVR. In the multivariate analysis by m ITT,the significant SVR factors were relapsers,IL28 B CC and non-F4; the type of treatment(BOC or TVR) was not significant. The lowest SVR values were presented by the F4-NR patients,treated with BOC(46%) or with TVR(45%). 28% of the patients interrupted the treatment,mainly by non-viral response(51%):this outcome was more frequent in the TE than in the TN patients(57% vs 40%,P = 0.01). With respect to severe haematological disorders,neutropaenia was more likely to affect the patients treated with BOC(33% vs 20%,P ≤ 0.0001),and thrombocytopaenia and anaemia,the F4 patients(P = 0.000,P = 0.025,respectively). CONCLUSION:In a real clinical practice setting with a high proportion of patients with advanced fibrosis,effectiveness of first-generation PIs was high except for NR patients,with similar SVR rates being achieved by BOC and TVR.

A Study on Heat Resistance and Initial Characterization of Protease Inhibitors in Porcine Colostrum

Porcine colostrum was separated into the acid soluble fraction (SF) and casein fraction (CF) by acidifying followed by centrifuge. SF was further separated by liquid chromatography and anisotropic membrane filtration. Capacities of the SF or CF of porcine colostrum, to inhibit trypsin and chymotrypsin activity and to inhibit the epidermal growth factor (EGF) degradation in pig small intestinal contents, were determined under different heat treatments. The study showed that trypsin inhibitors in porcine colostrum survived heat treatments of 100℃ water bath for up to 10 min, but exposure to boiling water bath for 30 min significantly decreased the inhibitory activity. Compared with the trypsin inhibitors, the chymotrypsin inhibitors were more heat sensitive. SF was more heat sensitive than CF. Separation of the SF of porcine colostrum by liquid chromatography and anisotropic membrane filtration revealed that the porcine colostrum protease inhibitors, those had the capacity to inhibit the trypsin chymotrypsin activity and enhanced the stability of EGF in the gastrointestinal(GI) lumen of weaned pigs, existed mainly in SF, milk derived, were a group of heat labile small proteins with molecular weight of 10 00050 000.

A Study on the Inhibitory Potency of Protease Inhibitorsin Porcine Colostrum

Porcine colostrum and milk were separated into the acid-soluble fraction(SF)and casein fraction(CF)by centrifuge. Trypsin and chymotrypsin inhibitory capacity in porcine colostrum, milk and their components were determined by incubating bovine trypsin or chymotrypsin in a medium. The inhibition of insulin-like growth factor I(IGF-I)and epidermal growth factor(EGF)degradation in pig small intestinal contents by porcine colostrum was measured by incubating iodinated IGF-I or EGF. Degradation of labeled IGF-I or EGF was determined by monitoring the generation of radioactivity soluble in 30% trichloroacetic acid(TCA). The results showed that porcine colostrum had high levels of trypsin and chymotrypsin inhibitory activity and increased the stability of IGF-I and EGF in pig intestinal contents. The SF was higher in inhibitory potency than CF. The present study revealed that the protease inhibitors in porcine colostrum, milk-derived and colostrum-specific, existed mainly in SF.

Lunasin protease inhibitor concentrate decreases pro-infl ammatory cytokines and improves histopathological markers in dextran sodium sulfate-induced ulcerative colitis

Lunasin protease inhibitor concentrate(LPIC)is a novel combination of soy bioactive peptide lunasin,Kunitz and Bowman-Birk protease inhibitors.The reported anti-inflammatory and anticancer properties of each one of them suggest LPIC as a promising candidate for the treatment of infl ammatory-related diseases.Our objective was to assess the in vivo anti-infl ammatory properties of LPIC.First,an in vitro test was performed in lipopolysaccharide(LPS)-activated RAW264.7 murine macrophages by measuring the production of nitric oxide(NO),interleukin-6(IL-6),and tumor necrosis factorα(TNF-α)as infl ammatory markers.For the in vivo model,ulcerative colitis(UC)was induced in mice via oral administration of dextran sodium sulfate(DSS).LPIC treatment was performed via daily intraperitoneal injection of 50 mg/kg body weight.Body weight,visible blood in stool and stool consistency were scored daily as macroscopic indicators of disease progression.Occult blood was evaluated by the presence of hemoglobin in stool every third day.Colon length,caecum weight,colonic myeloperoxidase activity(MPO),presence of pro-inflammatory cytokines in blood and colon,changes in the architecture,and expression of inducible nitric oxide synthase(i NOS)in colonic tissue were evaluated.In vitro,LPIC induced production of NO and maintained cytokine levels in comparison to activated untreated macrophages.In vivo,LPIC increased colonic bleeding and did not improve macroscopic markers of the disease,but reduced colonic IL-1βand IL-6,decreased systemic circulation of TNF-α,attenuated neutrophils infi ltration and i NOS expression in colonic tissue,and diminished the damage in colonic architecture.Our results suggest that combinations of peptides in LPIC may counteract the antiinfl ammatory properties in vitro;while in vivo,LPIC can signifi cantly reduce the histopathological damage,hence is a possible therapeutic strategy to attenuate UC.

Screening of Protease Inhibitory Activity in Aqueous Extracts of Marine Invertebrates from Cuban Coast

Protease inhibitors have been isolated from many variable sources;however, the need to identify and characterize new molecules has increased with the discovery of new therapeutic targets and the lack of specificity of already identified compounds with inhibitory activity. The goal of this work was to search for inhibitory activity against four proteolytic enzymes already recognized as therapeutic targets: human neutrophil elastase, dipeptidyl peptidase IV, subtilisin from Bacillus licheniformis and cathepsin K in selected marine invertebrates from the Caribbean Sea. A systematic screening was carried out with selected aqueous extracts belonging to 20 species from seven different phyla: Annelida, Bryozoa, Chordata, Cnidaria, Equinodermata, Mollusca and Porifera, all collected at the coast of Havana (Cuba). All extracts showing initial inhibitory activity were characterized in terms of IC50 values and specific inhibitory activity (SIA). Model enzymes were used in the case of human neutrophil elastase (porcine pancreatic elastase) and cathepsin K (papain) for the screening and all positive results were confirmed by testing toward the therapeutic targets. Ten extracts were identified showing inhibitory activity against human neutrophil elastase, for which the most promising values were obtained for Nerita peloronta. Only one extract, Bunodosoma granulifera, showed inhibitory activity against dipeptidyl peptidase IV with rather poor values of IC50 and SIA. Seven extracts showed inhibitory activity against B. licheniformis subtilisin with very good IC50 and SIA values for Lissodendorix isodyctialis, Cenchritis muricatus, and N. peloronta. Finally, eight extracts were positive for cathepsin K with almost similar parameters values among them. All these results confirmed the richness and potential of the marine invertebrate’s fauna and indicated new promising sources for the identification of natural compounds with potential application in therapeutics.

Protease inhibitors in Bombyx mori silk might participate in protecting the pupating larva from microbial infection

Pupae inside cocoons rarely suffer from disease. It is apparent that some factors in the cocoon exert antimicrobial effects whereby the pupae inside can be protected from microbial infection. In the present study, we investigated the expression of cocoon protease inhibitors using immunoblotting and activity staining. Enzymatic hydrolysis of cocoon proteins in vitro was performed to characterize their roles in protecting the cocoon from microbial proteases. We found that some protease inhibitors, particularly trypsin inhibitor-like （TIL）-type protease inhibitors, can be secreted into the cocoon layer during the spinning process, thereby providing effective protection to the cocoon and pupa by inhibiting the extracellular proteases that can be secreted by pathogens.

Protease inhibitors:recent advancement in its usage as a potential biocontrol agent for insect pest management

Plant derived protease inhibitors(PIs)are a promising defensin for crop im-provement and insect pest management.Although agronomist made significant efforts in utilizing PIs for managing insect pests.the potentials of PIs are still obscured.Insect ability to compensate nutrient starvation induced by dietary PI feeding using different strategies,that is,overexpression of PI-sensitive protease,expression of PI-insensitive proteases,degradation of PI,has made this innumerable collection of PIs worthless.A practical challenge for agronomist is to identify potent PI candidates,to limit insect compensatory responses and to elucidate insect compensatory and resistance mechanisms activated upon herbivory.This knowledge could be further efficiently utilized to identify potential targets for RNAi-mediated pest control.These vital genes of insects could be functionally anno-tated using the advanced gene-editing technique,CRISPR/Cas9.Contemporary research is exploiting different in silico and modern molecular biology techniques to utilize PIs in controlling insect pests efficiently.This review is structured to update recent advancements in this field,along with is chronological background.

Cryo-EM structures reveal the dynamic transformation of human alpha-2-macroglobulin working as a protease inhibitor

Human alpha-2-macroglobulin is a well-known inhibitor of a broad spectrum of proteases and plays important roles in immunity,inflammation,and infections.Here,we report the cryo-EM structures of human alpha-2-macroglobulin in its native state,induced state transformed by its authentic substrate,human trypsin,and serial intermediate states between the native and fully induced states.These structures exhibit distinct conformations,which reveal the dynamic transformation of alpha-2-macroglobulin that acts as a protease inhibitor.The results shed light on the molecular mechanism of alpha-2-macroglobulin in entrapping substrates.

Effects of inhibitors on the protease profiles and degradation of activated Cry toxins in larval midgut juices of Cnaphalocrocis medinalis (Lepidoptera:Pyralidae)

Midgut juice plays an important role in food digestion and detoxification in insects.In order to understand the potential of midgut juice of Cnaphalocrocis medinalis(Guenée)to degrade Bt proteins,the enzymatic activity of midgut juice and its degradation of Bt proteins(Cry2A,Cry1C,Cry1Aa,and Cry1Ac)were evaluated in this study through protease inhibitor treatments.The activities of total protease in midgut juices were significantly inhibited by phenylmethylsulfonyl fluoride(PMSF),tosyl-L-lysine chloromethyl ketone(TLCK),pepstatin A and leupeptin.The enzymatic activity of chymotrypsin was significantly inhibited by PMSF,and enzymatic activity of trypsin was significantly inhibited by ethylenediaminetetraacetic acid(EDTA),PMSF,tosyl phenylalanine chloromethyl ketone(TPCK),TLCK and trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane(E-64).EDTA could significantly inhibit the degradation of Cry2A by C.medinalis.EDTA,PMSF,TPCK,and TLCK could inhibit the degradation of Cry1C and Cry1Aa.EDTA,PMSF,TPCK,TLCK,and E-64 could inhibit the degradation of Cry1Ac.Our results indicated that some protease inhibitors hindered various enzymatic activities in the larval midgut of C.medinalis,which may reduce the insect’s ability to degrade Bt toxins.These findings may aid the application of protease inhibitors in the management of this insect pest in the future.

Protease inhibitor in scorpion (Mesobuthus eupeus) venom prolongs the biological activities of the crude venom

It is hypothesized that protease inhibitors play an essential role in survival of venomous animals through protecting peptide/protein toxins from degradation by proteases in their prey or predators. However, the biological function of protease inhibitors in scorpion venoms remains unknown. In the present study, a trypsin inhibitor was purified and characterized from the venom of scorpion Mesobuthus eupeus, which enhanced the biological activities of crude venom components in mice when injected in combination with crude venom. This protease inhibitor, named Me KTT-1, belonged to Kunitz-type toxins subfamily. Native Me KTT-1 selectively inhibited trypsin with a K_i value of 130 nmol×L^(–1). Furthermore, Me KTT-1 was shown to be a thermo-stable peptide. In animal behavioral tests, Me KTT-1 prolonged the pain behavior induced by scorpion crude venom, suggesting that protease inhibitors in scorpion venom inhibited proteases and protect the functionally important peptide/protein toxins from degradation, consequently keeping them active longer. In conclusion, this was the first experimental evidence about the natural existence of serine protease inhibitor in the venom of scorpion Mesobuthus eupeus, which preserved the activity of venom components, suggests that scorpions may use protease inhibitors for survival.

3,5-Bis(arylidene)-4-piperidones as potential dengue protease inhibitors

Dengue is a severe mosquito-borne viral infection causing half a million deaths annually. Dengue virus NS2B/NS3 protease is a validated target for anti-dengue drug design. A series of hitherto unreported 3,5-bis(arylidene)-4-piperidones analogues 4a4j were synthesized and screened in silico against DENV2 NS2B/NS3 protease to elucidate their binding mechanism and orientation around the active sites. Results were validated through an in vitro DENV2 NS2B/NS3 protease assay using a fluorogenic Boc-Gly-Arg-Arg-AMC substrate. Nitro derivatives of 3,5-bis(arylidene)-4-piperidones (4e and 4j) emerged as promising lead molecules for novel protease inhibitors with an IC50 of 15.22 and 16.23 µmol/L, respectively, compared to the standard, panduratin A, having IC50 of 57.28 µmol/L.

Comparative Antiviral Efficacy of Viral Protease Inhibitors against the Novel SARS-CoV-2 In Vitro

The recent outbreak of novel coronavirus pneumonia(COVID-19)caused by a new coronavirus has posed a great threat to public health.Identifying safe and effective antivirals is of urgent demand to cure the huge number of patients.Virusencoded proteases are considered potential drug targets.The human immunodeficiency virus protease inhibitors(lopinavir/ritonavir)has been recommended in the global Solidarity Trial in March launched by World Health Organization.However,there is currently no experimental evidence to support or against its clinical use.We evaluated the antiviral efficacy of lopinavir/ritonavir along with other two viral protease inhibitors in vitro,and discussed the possible inhibitory mechanism in silico.The in vitro to in vivo extrapolation was carried out to assess whether lopinavir/ritonavir could be effective in clinical.Among the four tested compounds,lopinavir showed the best inhibitory effect against the novel coronavirus infection.However,further in vitro to in vivo extrapolation of pharmacokinetics suggested that lopinavir/ritonavir could not reach effective concentration under standard dosing regimen[marketed as Kaletraò,contained lopinavir/ritonavir(200 mg/50 mg)tablets,recommended dosage is 400 mg/10 mg(2 tablets)twice daily].This research concluded that lopinavir/ritonavir should be stopped for clinical use due to the huge gap between in vitro IC50 and free plasma concentration.Nevertheless,the structure–activity relationship analysis of the four inhibitors provided further information for de novel design of future viral protease inhibitors of SARS-CoV-2.