Mediating effect of work stress in the relationship between fear of COVID-19 and nurses’ organizational and professional turnover intentions (preprint)

Nursing is one of the most stressful and high-risk professions. It is important to identify the psychological problems experienced by nurses during the COVID-19 pandemic and examine the relationship between these problems to devise measures that can properly address them. This study examined mediating effect of work stress in the relationship between fear of COVID-19 and nurses’ organizational and professional turnover intentions. Using a cross-sectional research design, this study was conducted on 486 nurses working in seven hospitals in Turkey. The mean age of the participants was 35.24±6.81 and 59.9% of them were women. The Fear of COVID-19 Scale, the General Work Stress Scale, and the Turnover Intention Scale were used to collect data. A mediation model showed that fear of COVID-19 was positively associated with work stress and organizational and professional turnover intentions. The model also revealed that work stress was positively associated with organizational and professional turnover intentions. Furthermore, the results demonstrated that fear of COVID-19 did not only have a direct effect on organizational and professional turnover intentions but also had an indirect effect on it via increased work stress. Findings improve our understanding of the role of work stress in the relationship between fear of COVID-19 and organizational and professional turnover intentions. The findings are fruitful for tailoring and implementing intervention programs to reduce the adverse psychological impacts of COVID-19 on nurses.

The Omicron Variant Increases the Interactions of SARS-CoV-2 Spike Glycoprotein with ACE2 (preprint)

Recently detected Omicron variant of SARS-CoV-2 (B.1.1.529) is heavily mutated on the receptor-binding domain (RBDOmicron) of its spike glycoprotein (S). RBD plays a critical role in viral infection by binding to the peptidase domain (PD) of angiotensin-converting enzyme 2 (ACE2) receptors in host cells. To investigate how Omicron mutations affect RBD-PD interactions, we performed all-atom molecular dynamics simulations of the RBDOmicron-PD in the presence of explicit water and ions. Simulations revealed that RBDOmicron exhibits a more dispersed interaction network on both sides of the RBD-PD interaction surface. Mutations resulted in an increased number of salt bridges and hydrophobic interactions between RBDOmicron and PD compared to wild-type RBD (RBDWT). Using the conformations sampled in each trajectory, the Molecular Mechanics Poisson-Boltzmann Surface Area (MMPBSA) method estimated ~44% stronger binding free energy for RBDOmicron compared to RBDWT, which may result in higher binding efficiency of the SARS-CoV-2 virus to infect host cells.

Binding mechanism of neutralizing Nanobodies targeting SARS-CoV-2 Spike Glycoprotein (preprint)

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) enters human cells upon binding of its spike (S) glycoproteins to ACE2 receptors. Several nanobodies neutralize SARS-CoV-2 infection by binding to the receptor-binding domain (RBD) of S protein, but the underlying mechanism is not well understood. Here, we identified an extended network of pairwise interactions between RBD and nanobodies H11-H4, H11-D4, and Ty1 by performing all-atom molecular dynamics (MD) simulations. Simulations of the nanobody-RBD-ACE2 complex revealed that H11-H4 more strongly binds to RBD without overlapping with ACE2 and triggers dissociation of ACE2 due to electrostatic repulsion. In comparison, Ty1 binding results in dissociation of ACE2 from RBD due to an overlap with the ACE2 binding site, whereas H11-D4 binding does not trigger ACE2 dissociation. Mutations in SARS-CoV-2 501Y.V1 and 501.V2 variants resulted in a negligible effect on RBD-ACE2 binding. However, the 501.V2 variant weakened H11-H4 and H11-D4 binding while strengthening Ty1 binding to RBD. Our simulations indicate that all three nanobodies can neutralize 501Y.V1 while Ty1 is more effective against the 501.V2 variant.

Critical Interactions Between the SARS-CoV-2 Spike Glycoprotein and the Human ACE2 Receptor (preprint)

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infects human cells upon binding of its spike (S) glycoproteins to ACE2 receptors and causes the coronavirus disease 2019 (COVID-19). Therapeutic approaches to prevent SARS-CoV-2 infection are mostly focused on blocking S-ACE2 binding, but critical residues that stabilize this interaction are not well understood. By performing all-atom molecular dynamics (MD) simulations, we identified an extended network of salt bridges, hydrophobic and electrostatic interactions, and hydrogen bonding between the receptor-binding domain (RBD) of the S protein and ACE2. Mutagenesis of these residues on the RBD was not sufficient to destabilize binding but reduced the average work to unbind the S protein from ACE2. In particular, the hydrophobic end of RBD serves as the main anchor site and unbinds last from ACE2 under force. We propose that blocking the hydrophobic surface of RBD via neutralizing antibodies could prove an effective strategy to inhibit S-ACE2 interactions.

Single-cell RNA Expression of SARS-CoV-2 Cell Entry Factors in Human Endometrium during Preconception (preprint)

We investigated potential SARS-CoV-2 tropism in human endometrium by single-cell RNA-sequencing of viral entry-associated genes in healthy women. Percentages of endometrial cells expressing ACE2, TMPRSS2, CTSB, or CTSL were <2%, 12%, 80%, and 80%, respectively, with 0.7% of cells expressing all four genes. Our findings imply low efficiency of SARS-CoV-2 infection in the endometrium before embryo implantation, providing information to assess preconception risk in asymptomatic carriers.

Ambroxol Hydrochloride Inhibits the Interaction between Severe Acute Respiratory Syndrome Coronavirus 2 Spike Protein's Receptor Binding Domain and Recombinant Human ACE2. (preprint)

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), enters the host cells through two main pathways, both involving key interactions between viral envelope-anchored spike glycoprotein of the novel coronavirus and the host receptor, angiotensin-converting enzyme 2 (ACE2). To date, SARS-CoV-2 has infected up to 26 million people worldwide; yet, there is no clinically approved drug or vaccine available. Therefore, a rapid and coordinated effort to re-purpose clinically approved drugs that prevent or disrupt these critical entry pathways of SARS-CoV-2 spike glycoprotein interaction with human ACE2, could potentially accelerate the identification and clinical advancement of prophylactic and/or treatment options against COVID-19, thus providing possible countermeasures against viral entry, pathogenesis and survival. Herein, we discovered that Ambroxol hydrochloride (AMB), and its progenitor, Bromhexine hydrochloride (BHH), both clinically approved drugs are potent effective modulators of the key interaction between the receptor binding domain (RBD) of SARS-CoV-2 spike protein and human ACE2. We also found that both compounds inhibited SARS-CoV-2 infection-induced cytopathic effect at micromolar concentrations. Therefore, in addition to the known TMPRSS2 activity of BHH; we report for the first time that the BHH and AMB pharmacophore has the capacity to target and modulate yet another key protein-protein interaction essential for the two known SARS-CoV-2 entry pathways into host cells. Altogether, the potent efficacy, excellent safety and pharmacologic profile of both drugs along with their affordability and availability, makes them promising candidates for drug repurposing as possible prophylactic and/or treatment options against SARS-CoV-2 infection.

Non-permissive SARS-CoV-2 infection of neural cells in the developing human brain and neurospheres (preprint)

Coronavirus disease 2019 (COVID-19) was initially described as a viral infection of the respiratory tract. It is now known, however, that many other biological systems are affected, including the central nervous system (CNS). Neurological manifestations such as stroke, encephalitis, and psychiatric conditions have been reported in COVID-19 patients, but its neurotropic potential is still debated. Here, we investigate the presence of SARS-CoV-2 in the brain from an infant patient deceased from COVID-19. The susceptibility to virus infection was compatible with the expression levels of viral receptor ACE2, which is increased in the ChP in comparison to other brain areas. To better comprehend the dynamics of the viral infection in neural cells, we exposed human neurospheres to SARS-CoV-2. Similarly to the human tissue, we found viral RNA in neurospheres, although viral particles in the culture supernatant were not infective. Based on our observations in vivo and in vitro, we hypothesize that SARS-CoV-2 does not generate productive infection in developing neural cells and that infection of ChP weakens the blood-cerebrospinal fluid barrier allowing viruses, immune cells, and cytokines to access the CNS, causing neural damage in the young brain.

SARS CoV-2 nucleocapsid protein forms condensates with viral genomic RNA (preprint)

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection causes COVID-19, a pandemic that seriously threatens global health. SARS CoV-2 propagates by packaging its RNA genome into membrane enclosures in host cells. The packaging of the viral genome into the nascent virion is mediated by the nucleocapsid (N) protein, but the underlying mechanism remains unclear. Here, we show that the N protein forms biomolecular condensates with viral RNA both in vitro and in mammalian cells. While the N protein forms spherical assemblies with unstructured RNA, it forms mesh like-structures with viral RNA strands that contain secondary structure elements. Cross-linking mass spectrometry identified an intrinsically-disordered region that forms interactions between N proteins in condensates, and truncation of this region disrupts phase separation. By screening 1,200 FDA approved drugs in vitro, we identified a kinase inhibitor nilotinib, which affects the morphology of N condensates in vitro and disrupts phase separation of the N protein in vivo. These results indicate that the N protein compartmentalizes viral RNA in infected cells through liquid-liquid phase separation, and this process can be disrupted by a possible drug candidate.