Damjanovic, A. | bioRxiv Science

bioRxiv2024

Quantitating SARS-CoV-2 Neutralizing Antibodies from Human Dried Blood Spots

BackgroundIn the earliest days of COVID-19 pandemic, the collection of dried blood spots (DBS) enabled public health laboratories to undertake population-scale seroprevalence studies to estimate rates of SARS-CoV-2 exposure. With SARS-CoV-2 seropositivity levels now estimated to exceed 94% in the United States, attention has turned to using DBS to assess functional (neutralizing) antibodies within cohorts of interest. MethodsContrived DBS eluates from convalescent, fully vaccinated and pre-COVID-19 serum samples were evaluated in SARS-CoV-2 plaque reduction neutralization titer (PRNT) assays, a SARS-CoV-2 specific 8-plex microsphere immunoassay, a cell-based pseudovirus assay, and two different spike-ACE2 inhibition assays, an in-house Luminex-based RBD-ACE2 inhibition assay and a commercial real-time PCR-based inhibition assay (NAB-Sure). ResultsDBS eluates from convalescent individuals were compatible with the spike-ACE2 inhibition assays, but not cell-based pseudovirus assays or PRNT. However, the insensitivity of cell-based pseudovirus assays was overcome with DBS eluates from vaccinated individuals with high SARS-CoV-2 antibody titers. ConclusionSARS-CoV-2 neutralizing titers can be derived with confidence from DBS eluates, thereby opening the door to the use of these biospecimens for the analysis of vulnerable populations and normally hard to reach communities.

immunology↗

bioRxiv2022

Intrinsically disordered interaction network in an RNA chaperone revealed by native mass spectrometry

RNA-binding proteins contain intrinsically disordered regions whose functions in RNA recognition are poorly understood. The RNA chaperone Hfq is a homohexamer that contains six flexible C-terminal domains (CTDs). The effect of the CTDs on Hfqs integrity and RNA binding has been challenging to study because of their sequence identity and inherent disorder. We used native mass spectrometry (nMS) coupled with surface-induced dissociation (SID) and molecular dynamics (MD) simulations to disentangle the arrangement of the CTDs and their impact on the stability of E. coli Hfq with and without RNA. The results show that the CTDs stabilize the Hfq hexamer through multiple interactions with the core and between CTDs. RNA binding perturbs this network of CTD interactions, destabilizing the Hfq ring. This destabilization is partially compensated by binding of RNAs that contact multiple surfaces of Hfq. By contrast, binding of short RNAs that only contact one or two subunits results in net destabilization of the complex. Together, the results show that a network of intrinsically disordered interactions integrate RNA contacts with the six subunits of Hfq. We propose that this CTD network raises the selectivity of RNA binding. Significance StatementHfq is a protein hexamer necessary for gene regulation by non-coding RNA in bacteria, during infection or under stress. In the cell, Hfq must distinguish its RNA partners from many similar nucleic acids. Mass spectrometry dissociation patterns, together with molecular dynamics simulations, showed that flexible extensions of each Hfq subunit form a dense network that interconnects the entire hexamer. This network is disrupted by RNA binding, but the lost interactions are compensated by RNAs that contact multiple Hfq subunits. By measuring interactions that are too irregular to be counted by other methods, mass spectrometry shows how flexible protein extensions help chaperones like Hfq recognize their RNA partners in the messy interior of the cell.

biophysics↗