QTQTN motif upstream of the furin-cleavage site plays a key role in SARS-CoV-2 infection and pathogenesis

The furin cleavage site (FCS), an unusual feature in the SARS-CoV-2 spike protein, has been spotlighted as a factor key to facilitating infection and pathogenesis by increasing spike processing. Similarly, the QTQTN motif directly upstream of the FCS is also an unusual feature for group 2B coronaviruses (CoVs). The QTQTN deletion has consistently been observed in in vitro cultured virus stocks and some clinical isolates. To determine whether the QTQTN motif is critical to SARS-CoV-2 replication and pathogenesis, we generated a mutant deleting the QTQTN motif (ΔQTQTN). Here, we report that the QTQTN deletion attenuates viral replication in respiratory cells in vitro and attenuates disease in vivo. The deletion results in a shortened, more rigid peptide loop that contains the FCS and is less accessible to host proteases, such as TMPRSS2. Thus, the deletion reduced the efficiency of spike processing and attenuates SARS-CoV-2 infection. Importantly, the QTQTN motif also contains residues that are glycosylated, and disruption of its glycosylation also attenuates virus replication in a TMPRSS2-dependent manner. Together, our results reveal that three aspects of the S1/S2 cleavage site—the FCS, loop length, and glycosylation—are required for efficient SARS-CoV-2 replication and pathogenesis.

SARS-CoV-2 emerged in late 2019 and has caused the largest pandemic since the 1918 influenza outbreak (1). An unusual feature of SARS-CoV-2 is the presence of a furin cleavage site (FCS) in its spike protein (2). The CoV spike is a trimer of spike proteins composed of the S1 and S2 subunits, responsible for receptor binding and membrane fusion, respectively (1). After receptor binding, the spike protein is proteolytically cleaved at the S1/S2 and S2′ sites to activate the fusion machinery. For SARS-CoV-2, the spike protein contains a novel cleavage motif recognized by the host cell furin protease (PRRAR) directly upstream of the S1/S2 cleavage site that facilitates cleavage prior to virion release from the producer cell. This FCS, not found in other group 2B CoVs, plays a key role in spike processing, infectivity, and pathogenesis as shown by our group and others (3, 4).Importantly, another novel amino acid motif, QTQTN, is found directly upstream of the FCS. This QTQTN motif, also absent in other group 2B CoVs, is often deleted and has been pervasive in cultured virus stocks of the alpha, beta, and delta variants (5–8). In addition, the QTQTN deletion has been observed in a small subset of patient samples as well (9–11). Because this deletion has been frequently identified, we set out to characterize it and determine whether it has consequences for viral replication and virulence. Using our infectious clone (12, 13), we demonstrated that the loss of this motif attenuates SARS-CoV-2 replication in respiratory cells in vitro and pathogenesis in hamsters. The QTQTN deletion results in reduced spike cleavage and diminished capacity to use serine proteases on the cell surface for entry. Importantly, mutations of glycosylation-enabling residues in the QTQTN motif results in similar replication attenuation despite intact spike processing. Together, our results highlight elements in the SARS-CoV-2 spike in addition to the FCS that contribute to increased replication and pathogenesis.     

Visible-light-induced one-pot synthesis of sulfonic esters via multicomponent reaction of arylazo sulfones and alcohols

Sulfonic ester is a chemical structure common to many organic molecules, including biologically active compounds. Herein, a visible-light-induced synthetic method to prepare aryl sulfonic ester from arylazo sulfones was developed. In the present study, a one-pot reaction was carried out using arylazo sulfones, DABSO (DABCO·(SO₂)₂), and alcohols in the presence of CuI as a coupling catalyst and HCl as an additive to yield sulfonic esters via multicomponent reaction. This synthetic method afforded a wide range of sulfonic esters with high yields under mild conditions.

Facile and efficient one-pot synthesis of sulfonic esters has been achieved via visible-light-induced multicomponent reaction of arylazo sulfones, and alcohols in the presence of DABSO, CuI, and HCI.     

Characterisation of the RNA Virome of Nine Ochlerotatus Species in Finland

RNA viromes of nine commonly encountered Ochlerotatus mosquito species collected around Finland in 2015 and 2017 were studied using next-generation sequencing. Mosquito homogenates were sequenced from 91 pools comprising 16–60 morphologically identified adult females of Oc. cantans, Oc. caspius, Oc. communis, Oc. diantaeus, Oc. excrucians, Oc. hexodontus, Oc. intrudens, Oc. pullatus and Oc. punctor/punctodes. In total 514 viral Reverse dependent RNA polymerase (RdRp) sequences of 159 virus species were recovered, belonging to 25 families or equivalent rank, as follows: Aliusviridae, Aspiviridae, Botybirnavirus, Chrysoviridae, Chuviridae, Endornaviridae, Flaviviridae, Iflaviridae, Negevirus, Partitiviridae, Permutotetraviridae, Phasmaviridae, Phenuiviridae, Picornaviridae, Qinviridae, Quenyavirus, Rhabdoviridae, Sedoreoviridae, Solemoviridae, Spinareoviridae, Togaviridae, Totiviridae, Virgaviridae, Xinmoviridae and Yueviridae. Of these, 147 are tentatively novel viruses. One sequence of Sindbis virus, which causes Pogosta disease in humans, was detected from Oc. communis from Pohjois-Karjala. This study greatly increases the number of mosquito-associated viruses known from Finland and presents the northern-most mosquito-associated viruses in Europe to date.     

Correction: Synthesis and characterizations of YZ-BDC:Eu3+,Tb3+ nanothermometers for luminescence-based temperature sensing

Correction for ‘Synthesis and characterizations of YZ-BDC:Eu³⁺,Tb³⁺ nanothermometers for luminescence-based temperature sensing’ by Lam Thi Kieu Giang et al., RSC Adv., 2022, 12, 13065–13073, https://doi.org/10.1039/D2RA01759H.

The authors regret the omission of a funding acknowledgement in the original article. This acknowledgement is given below.Karolina Trejgis is supported by the Foundation for Polish Science (FNP).The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Hemangiomas of the external auditory canal:a literature review and two new case reports

Aim  

The aim of this paper is to present two case reports of patients with hemangiomas of the external auditory canal, and to overview all cases published in English language literature so far.     

Endemic Norovirus Infections in Children,Ho Chi Minh City,Vietnam, 2009–2010

We performed a case–control investigation to identify risk factors for norovirus infections among children in Vietnam. Of samples from 1,419 children who had diarrhea and 609 who were asymptomatic, 20.6% and 2.8%, respectively, were norovirus positive. Risk factors included residential crowding and symptomatic contacts, indicating person-to-person transmission of norovirus.     

Further evidence of construct validity of standardized patient‐based performance examinations

The purpose of this study was to gather additional evidence pertinent to the construct validity of standardized patient‐based clinical performance examinations. Specifically, the study determined whether students who indicated they had previously read about, seen, or worked up a case on the examination performed differently on that case from those students who had not. Overall, it was found that students with previous reading or direct experiences with cases on the test tended to have higher case mean scores on those cases than those who had not. These results demonstrated that scores on standardized patient‐based performance examinations are sensitive to the examinees’ various learning experiences.     

Transplant of rhesus-positive bone marrow in a rhesus-negative woman having anti-rhesus D alloantibodies

A woman affected by acute myeloblastic leukemia was grafted with HLA A, B and D compatible rhesus-positive bone marrow from her brother. Before grafting, she had anti-D alloantibodies (1/512 IAT, 2.9 micrograms/ml). To prevent the destruction of donor red blood cells, four plasma exchanges and a conditioning regimen (total-body irradiation 800 rad, cyclophosphamide, methotrexate) were carried out to decrease anti-D from 2.9 to less than 0.02 micrograms/ml on day 0. The anti-D level was 0.8 micrograms/ml on day 12 and was decreased to 0.2 micrograms/ml by eight plasma exchanges until day 35. Anti-D antibodies were undetectable with Lalezari's technique on day 45. Engraftment was obtained on day 25 (3,000 leukocytes/mm3 and 50% erythroblasts in bone marrow). The patient died from aspergillosis and graft-versus-host disease on day 54. This observation shows that an engraftment of rhesus-positive bone marrow in a recipient with anti-D antibody is possible.