Uusinta tietoa uudesta koronaviruksesta(3) Orf3b ja jokin aivan uusi proteiini

 

 

Articles

Genomic characterization of the 2019 novel human-pathogenic coronavirus isolated from a patient with atypical pneumonia after visiting Wuhan

Jasper Fuk-Woo Chan, Kin-Hang Kok, Zheng Zhu, Hin Chu, Kelvin Kai-Wang To, Shuofeng Yuan & show all

Pages 221-236 | Received 16 Jan 2020, Accepted 17 Jan 2020, Published online: 28 Jan 2020

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• https://doi.org/10.1080/22221751.2020.1719902

Orf3b

A novel short putative protein with 4 helices and no homology to existing SARS-CoV or SARS-r-CoV protein was found within Orf3b (Figure 4).
 It is notable that SARS-CoV deletion mutants lacking orf3b replicate to levels similar to those of wild-type virus in several cell types [19], suggesting that orf3b is dispensable for viral replication in vitro.
But orf3b may have a role in viral pathogenicity as Vero E6 but not 293T cells transfected with a construct expressing Orf3b underwent necrosis as early as 6 h after transfection and underwent simultaneous necrosis and apoptosis at later time points [20].

Orf3b was also shown to inhibit expression of IFN-β at synthesis and signalling [21].
 Subsequently, orf3b homologues identified from three bat SARS-related-CoV strains were C-terminally truncated and lacked the C-terminal nucleus localization signal (NLS) of SARS-CoV [22].
 IFN antagonist activity analysis demonstrated that one SARS-related-CoV orf3b still possessed IFN antagonist and IRF3-modulating activities.
These results indicated that different orf3b proteins display different IFN antagonist activities and this function is independent of the protein's nuclear localization, suggesting a potential link between bat SARS-related-CoV orf3b function and pathogenesis.
 The importance of this new protein in 2019-nCoV will require further validation and study.

Figure 4. Analysis of orf3b. A. Multiple alignment of orf3b protein sequence between 2019-nCoV (HKU-SZ-005b), SARS-CoV and SARS-related CoV. B. A novel putative short protein found in orf3b.

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Orf8

orf8 is an accessory protein found in the Betacoronavirus lineage B coronaviruses. Human SARS-CoVs isolated from early-phase patients, all civet SARS-CoVs, and other bat SARS-related CoVs contain full-length orf8 [23]. However, a 29-nucleotide deletion, which causes the split of full length of orf8 into putative orf8a and orf8b, has been found in all SARS-CoV isolated from mid- and late- phase human patients [24]. In addition, we have previously identified two bat SARS-related-CoV (Bat-CoV YNLF_31C and YNLF_34C) and proposed that the original SARS-CoV full-length orf8 is acquired from these two bat SARS-related-CoV [25]. Since the SARS-CoV is the closest human pathogenic virus to the 2019-nCoV, we performed phylogenetic analysis and multiple alignments to investigate the orf8 amino acid sequences. The orf8 protein sequences used in the analysis derived from early phase SARS-CoV that includes full-length orf8 (human SARS-CoV GZ02), the mid- and late-phase SARS-CoV that includes the split orf8b (human SARS-CoV Tor2), civet SARS-CoV (paguma SARS-CoV), two bat SARS-related-CoV containing full-length orf8 (bat-CoV YNLF_31C and YNLF_34C), 2019-nCoV, the other two closest bat SARS-related-CoV to 2019-nCoV SL-CoV ZXC21 and ZC45), and bat SARS-related-CoV HKU3-1 (Figure 5(A)). As expected, orf8 derived from 2019-nCoV belongs to the group that includes the closest genome sequences of bat SARS-related-CoV ZXC21 and ZC45. Interestingly, the new 2019-nCoV orf8 is distant from the conserved orf8 or orf8b derived from human SARS-CoV or its related viruses derived from civet (paguma SARS-CoV) and bat (bat-CoV YNLF_31C and YNLF_34C). This new orf8 of 2019-nCoV does not contain known functional domain or motif. An aggregation motif VLVVL (amino acid 75–79) has been found in SARS-CoV orf8b (Figure 5(B)) which was shown to trigger intracellular stress pathways and activates NLRP3 inflammasomes [26], but this is absent in this novel orf8 of 2019-nCoV. Based on a secondary structure prediction, this novel orf8 has a high possibility to form a protein with an alpha-helix, following with a beta-sheet(s) containing six strands (Figure 5(C)).

Figure 5. Analysis of orf8 to show novel putative protein. (A) Phylogenetic analysis of orf8 amino acid sequences of 2019-nCoV HKU-SZ-005b (accession number MN975262), bat SARS-like coronavirus isolates bat-SL-CoVZXC21 and bat-SL-CoVZXC45 (accession number MG772934.1 and MG772933.1, respectively) and human SARS coronavirus (accession number AY274119) was performed using the neighbour-joining method with bootstrap 1000. The evolutionary distances were calculated using the JTT matrix-based method. (B) Multiple alignment was performed and displayed using CLUSTAL 2.1 and BOXSHADE 3.21, respectively. The black background represents the identity while the grey background represents the similarity of the amino acid sequences. (C) Structural analysis of Orf8 was performed using PSI-blast-based secondary structure PREDiction (PSIPRED). Predicted helix structure (h) and strand (s) were boxed with red and yellow respectively.

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Phylogenetic relationship among 2019-nCoV and other βCoVs

The genome of 2019-nCoV has overall 89% nucleotide identity with bat SARS-related-CoV SL-CoVZXC21 (MG772934.1), and 82% with human SARS-CoV BJ01 2003 (AY278488) and human SARS-CoV Tor2 (AY274119). The phylogenetic trees constructed using the amino acid sequences of orf1a/b and the 4 structural genes (S, E, M, and N) were shown (Figure 6(A–E)). For all these 5 genes, the 2019-nCoV was clustered with lineage B βCoVs. It was most closely related to the bat SARS-related CoVs ZXC21 and ZC45 found in Chinese horseshoe bats (Rhinolopus sinicus) collected from Zhoushan city, Zhejiang province, China between 2015 and 2017. Thus this novel coronavirus should belong to the genus Betacoronavirus, subgenus Sabecovirus (previously lineage 2b of Group 2 coronavirus). SARS-related coronaviruses have been found continuously especially in horseshoe bat species in the last 13 years. Between 2003 and 2018, 339 complete SARS-related coronavirus genomes have been sequenced, including 274 human SARS-CoV, 18 civet SARS coronavirus, and 47 bat SARS-related coronaviruses mainly from Rhinolophus bat species. Together, they formed a distinct subclade among other lineage B βCoVs. These results suggested that the 2019-nCoV might have also originated from bats. But we cannot ascertain whether another intermediate or amplification animal host infected by 2019-nCoV could be found in the epidemiological market, just as in the case of Paguma civets for SARS-CoV.

Figure 6. Phylogenetic tree construction by the neighbour joining method was performed using MEGA X software, with bootstrap values being calculated from 1000 trees using amino acid sequences of (A) orf1ab polypeptide; (B) Spike glycoprotein; (C) Envelope protein; (D) Membrane protein; (E) Nucleoprotein.

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RNA secondary structures

As shown in Figure 7(A–C), the SARS-CoV 5′-UTR contains SL1, SL2, SL3, SL4, S5, SL5A, SL5B, SL5C, SL6, SL7, and SL8. The SL3 contains trans–cis motif [27]. The SL1, SL2, SL3, SL4, S5, SL5A, SL5B, and SL5C structures were similar among the 2019-nCoV, human SARS-CoV and the bat SARS-related ZC45. In the 2019-nCoV, part of the S5 found was inside the orf1a/b (marked in red), which was similar to SARS-CoV. In bat SARS-related CoV ZC45, the S5 was not found inside orf1a/b. The 2019-nCoV had the same SL6, SL7, and SL8 as SARS-CoV, and an additional stem loop. Bat SARS-related CoV ZC45 did not have the SARS-COV SL6-like stem loop. Instead, it possessed two other stem loops in this region. All three strains had similar SL7 and SL8. The bat SARS-like CoV ZC45 also had an additional stem loop between SL7 and SL8. Overall, the 5′-UTR of 2019-nCoV was more similar to that of SARS-CoV than the bat SARS-related CoV ZC 45. The biological relevance and effects of virulence of the 5′-UTR structures should be investigated further. The 2019-nCoV had various 3′-UTR structures, including BSL, S1, S2, S3, S4, L1, L2, L3, and HVR (Figure 7(D–F)). The 3′-UTR was conserved among 2019-nCoV, human SARS-CoV and SARS-related CoVs [27].

Figure 7. Secondary structure prediction and comparison in the 5′-untranslated region (UTR) and 3′-UTR using the RNAfold WebServer (with minimum free energy and partition function in Fold algorithms and basic options. The SARS 5′- and 3′- UTR was used as a reference to adjust the prediction results.(A) SARS-CoV 5'-UTR; (B) 2019-nCoV (HKU-SZ-005b) 5'-UTR; (C) ZC45 5'-UTR; (D) SARS-CoV 3'-UTR; (E) 2019-nCoV (HKU-SZ-005b) 3'-UTR; (F) ZC45 3'-UTR.

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In summary, 2019-nCoV is a novel lineage B Betacoronavirus closely related to bat SARS-related coronaviruses. It also has unique genomic features which deserves further investigation to ascertain their roles in viral replication cycle and pathogenesis. More animal sampling to determine its natural animal reservoir and intermediate animal host in the market is important. This will shed light on the evolutionary history of this emerging coronavirus which has jumped into human after the other two zoonotic Betacoroanviruses, SARS-CoV and MERS-CoV.

Acknowledgements

The funding sources had no role in the study design, data collection, analysis, interpretation, or writing of the report.

Disclosure statement

No potential conflict of interest was reported by the author(s).

ORCID

Jasper Fuk-Woo Chan http://orcid.org/0000-0001-6336-6657
Kin-Hang Kok http://orcid.org/0000-0003-3426-332X

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Additional information

Funding

This study was partly supported by the donations of Michael Seak-Kan Tong, Respiratory Viral Research Foundation Limited, Hui Ming, Hui Hoy and Chow Sin Lan Charity Fund Limited, Chan Yin Chuen Memorial Charitable Foundation, Marina Man-Wai Lee, and the Hong Kong Hainan Commercial Association South China Microbiology Research Fund; and funding from the Consultancy Service for Enhancing Laboratory Surveillance of Emerging Infectious Diseases and Research Capability on Antimicrobial Resistance for Department of Health of the Hong Kong Special Administrative Region Government; the Theme-Based Research Scheme (T11/707/15) of the Research Grants Council, Hong Kong Special Administrative Region; Sanming Project of Medicine in Shenzhen, China (No. SZSM201911014); and the High Level-Hospital Program, Health Commission of Guangdong Province, China.