Reply to Yan et al.: Quercetin possesses a fluorescence quenching effect but is a weak inhibitor against SARS-CoV-2 main protease
Haiyu Xu, Yute Zhong, Jinyue Yang, Lifeng Fu, Yi Shi, Luqi Huang, George F Gao
Proceedings of the National Academy of Sciences, doi:10.1073/pnas.2309870120
Recently, we published an article (1) showing that several bioactive compounds were identified from Huashi Baidu decoction (Q-14) that showed both antiviral activity and antiinflammatory effects against COVID-19. The main protease (M pro ) of SARS-CoV-2 is an attractive target for the development of antiviral drugs. Our results showed that quercetin and echinatin from Q-14 displayed moderate inhibition activities against SARS-CoV-2 M pro at submicromolar levels by the fluorescence resonance energy transfer (FRET)-based protease activity assay. However, Yan et al. suggested that quercetin is a promiscuous M pro inhibitor because of its fluorescence quenching effect (2). We took this suspicion very seriously. Therefore, we repeated the FRET-based protease activity assay and tested the fluorescence quenching effects with the MCA-AVLQ-Lys (Dnp)-Lys-NH2 (MCA-AVLQ) fragment. The FRET assay results showed that both quercetin and echinatin have M pro inhibition activity (Fig. 1 A and E ), but both quercetin and echinatin displayed a fluorescence quenching effect on MCA-AVLQ fragment (Fig. 1 B and F ). The inhibition ratio and quenching ratio were further calculated (Fig. 1 C and G). We found that the inhibition ratio is significantly greater than the quenching rate, especially at low concentrations, which indicates that quercetin and echinatin should possess certain M pro inhibition activity. To further validate the M pro inhibition activity of
References
Xu, Bioactive compounds from Huashi Baidu decoction possess both antiviral and anti-inflammatory effects against COVID-19, Proc. Natl. Acad. Sci. U.S.A
Yan, Production of a versatile SARS-CoV-2 main protease biosensor based on a dimerization-dependent red fluorescent protein, J. Med. Virol
Yan, Zhang, Liu, Wang, Chen, Reframing quercetin as a promiscuous inhibitor against SARS-CoV-2 main protease, Proc. Natl. Acad. Sci. U.S.A
{ 'indexed': {'date-parts': [[2023, 9, 6]], 'date-time': '2023-09-06T05:09:07Z', 'timestamp': 1693976947450},
'reference-count': 0,
'publisher': 'Proceedings of the National Academy of Sciences',
'issue': '37',
'license': [ { 'start': { 'date-parts': [[2023, 9, 5]],
'date-time': '2023-09-05T00:00:00Z',
'timestamp': 1693872000000},
'content-version': 'vor',
'delay-in-days': 0,
'URL': 'https://creativecommons.org/licenses/by/4.0/'}],
'content-domain': {'domain': ['www.pnas.org'], 'crossmark-restriction': True},
'published-print': {'date-parts': [[2023, 9, 12]]},
'DOI': '10.1073/pnas.2309870120',
'type': 'journal-article',
'created': {'date-parts': [[2023, 9, 5]], 'date-time': '2023-09-05T17:52:22Z', 'timestamp': 1693936342000},
'update-policy': 'http://dx.doi.org/10.1073/pnas.cm10313',
'source': 'Crossref',
'is-referenced-by-count': 0,
'title': 'Reply to Yan et al.: Quercetin possesses a fluorescence quenching effect but is a weak inhibitor '
'against SARS-CoV-2 main protease',
'prefix': '10.1073',
'volume': '120',
'author': [ { 'given': 'Haiyu',
'family': 'Xu',
'sequence': 'first',
'affiliation': [ { 'name': 'Institute of Chinese Materia Medica, Academy of Chinese Medical '
'Sciences, Beijing 100700, China'}]},
{ 'given': 'Yute',
'family': 'Zhong',
'sequence': 'additional',
'affiliation': [ { 'name': 'Institute of Chinese Materia Medica, Academy of Chinese Medical '
'Sciences, Beijing 100700, China'}]},
{ 'given': 'Jinyue',
'family': 'Yang',
'sequence': 'additional',
'affiliation': [ { 'name': 'Chinese Academy of Sciences Key Laboratory of Pathogen '
'Microbiology and Immunology, Institute of Microbiology, Chinese '
'Academy of Sciences, Beijing 100101, China'}]},
{ 'given': 'Lifeng',
'family': 'Fu',
'sequence': 'additional',
'affiliation': [ { 'name': 'Chinese Academy of Sciences Key Laboratory of Pathogen '
'Microbiology and Immunology, Institute of Microbiology, Chinese '
'Academy of Sciences, Beijing 100101, China'}]},
{ 'given': 'Yi',
'family': 'Shi',
'sequence': 'additional',
'affiliation': [ { 'name': 'Chinese Academy of Sciences Key Laboratory of Pathogen '
'Microbiology and Immunology, Institute of Microbiology, Chinese '
'Academy of Sciences, Beijing 100101, China'}]},
{ 'given': 'Luqi',
'family': 'Huang',
'sequence': 'additional',
'affiliation': [ { 'name': 'State Key Laboratory of Dao-di Herbs, National Resource Center '
'for Chinese Materia Medica, China Academy of Chinese Medical '
'Sciences, Beijing 100700, China'}]},
{ 'ORCID': 'http://orcid.org/0000-0002-3869-615X',
'authenticated-orcid': False,
'given': 'George F.',
'family': 'Gao',
'sequence': 'additional',
'affiliation': [ { 'name': 'Chinese Academy of Sciences Key Laboratory of Pathogen '
'Microbiology and Immunology, Institute of Microbiology, Chinese '
'Academy of Sciences, Beijing 100101, China'}]}],
'member': '341',
'published-online': {'date-parts': [[2023, 9, 5]]},
'container-title': 'Proceedings of the National Academy of Sciences',
'original-title': [],
'language': 'en',
'link': [ { 'URL': 'https://pnas.org/doi/pdf/10.1073/pnas.2309870120',
'content-type': 'unspecified',
'content-version': 'vor',
'intended-application': 'similarity-checking'}],
'deposited': { 'date-parts': [[2023, 9, 5]],
'date-time': '2023-09-05T17:52:43Z',
'timestamp': 1693936363000},
'score': 1,
'resource': {'primary': {'URL': 'https://pnas.org/doi/10.1073/pnas.2309870120'}},
'subtitle': [],
'short-title': [],
'issued': {'date-parts': [[2023, 9, 5]]},
'references-count': 0,
'journal-issue': {'issue': '37', 'published-print': {'date-parts': [[2023, 9, 12]]}},
'alternative-id': ['10.1073/pnas.2309870120'],
'URL': 'http://dx.doi.org/10.1073/pnas.2309870120',
'relation': {},
'ISSN': ['0027-8424', '1091-6490'],
'subject': ['Multidisciplinary'],
'container-title-short': 'Proc. Natl. Acad. Sci. U.S.A.',
'published': {'date-parts': [[2023, 9, 5]]},
'assertion': [ { 'value': '2023-09-05',
'order': 2,
'name': 'published',
'label': 'Published',
'group': {'name': 'publication_history', 'label': 'Publication History'}}]}
