Biology subjects

Blomqvist, E. K.

Publications and source records attributed to Blomqvist, E. K..

3 recordsLinked to original sources

bioRxiv2025

MERS-CoV antagonizes PKR activation by inhibiting its condensation at viral replication complexes

Middle East respiratory syndrome coronavirus (MERS-CoV) is a highly pathogenic virus that antagonizes innate immune responses, including the protein kinase R (PKR) pathway. Here, we examine the process of PKR activation in response to an immunostimulatory MERS-CoV mutant encoding an inactive endoribonuclease U and a deletion of accessory protein NS4a. We show that PKR condenses and activates on viral dsRNA proximal to viral double-membrane vesicles (DMVs). Condensates composed of activated PKR disassociate from dsRNA and dissolve, releasing activated PKR molecules into the cytosol where they phosphorylate eIF2 to initiate the integrated stress response. MERS-CoV NS4a protein prevents PKR activation by condensing on dsRNA and occluding PKR binding. Lastly, PKR condensation coincided with its activation in response to Zika virus. These findings establish a comprehensive model for PKR activation in response to positive-strand RNA viruses that replicate within membrane-associated complexes and elucidate how MERS-CoV antagonizes this crucial antiviral pathway. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/670656v1_ufig1.gif" ALT="Figure 1"> View larger version (53K): org.highwire.dtl.DTLVardef@130c4b1org.highwire.dtl.DTLVardef@c16a1borg.highwire.dtl.DTLVardef@1d4023org.highwire.dtl.DTLVardef@5dbaea_HPS_FORMAT_FIGEXP M_FIG C_FIG HIGHLIGHTSO_LIPKR condenses on viral dsRNA exposed at membrane-associated replication complexes C_LIO_LIPKR condensation initiates autophosphorylation of PKR C_LIO_LIActivated p-PKR molecules disassociate from dsRNA and re-localize to the cytosol C_LIO_LIMERS-CoV NS4a inhibits PKR activation by occluding PKR condensation on dsRNA. C_LI

immunology↗

bioRxiv2023

Unstructured Domains in Assembly Factors Promote the Hierarchy of Ribosome Maturation via Their Structural Plasticity.

Ribosomes are assembled with the help of a large machinery of assembly factors (AFs), whose roles remain incompletely characterized. Recent structural studies of assembly intermediates have provided tremendous context for such studies and helped reveal novel roles, including as RNA chaperones. These structures have also revealed that a subset of the AFs have entirely non-globular structures, or large non-globular extensions, which extend across the assembling ribosomal subdomains, contacting many rRNA regions, ribosomal proteins (RPs) and other AFs. How these unusual structures could help promote assembly has remained unclear although it has been suggested that their potential for making multiple interactions helps constrain early assembly steps. By studying the roles of the AF Ltv1, an entirely non-globular protein, during late maturation steps of the 40S subunits head, we show here how the structural plasticity that derives from the non-globular structure is used to communicate maturation steps across the nascent subunit, thereby establishing the previously described hierarchy in head assembly. Our data indicate that while this structural plasticity enables integration of distinct folding and assembly steps, it also creates the potential for mutations that allow for bypass of these QC steps. These mutations are pathogenic in humans, further demonstrating the importance of proper 40S subunit assembly for protein homeostasis.

biochemistry↗

bioRxiv2023

A disease associated mutant reveals how Ltv1 orchestrates RP assembly and rRNA folding of the small ribosomal subunit head

Ribosomes are complex macromolecules assembled from 4 rRNAs and 79 ribosomal proteins (RPs). Their assembly is organized in a highly hierarchical manner, which is thought to avoid dead-end pathways, thereby enabling efficient assembly of ribosomes in the large quantities needed for healthy cellular growth. Moreover, hierarchical assembly also can help ensure that each RP is included in the mature ribosome. Nonetheless, how this hierarchy is achieved remains unknown, beyond the examples that depend on direct RP-RP interactions, which account for only a fraction of the observed dependencies. Using assembly of the small subunit head and a disease-associated mutation in the assembly factor Ltv1 as a model system, we dissect here how the hierarchy in RP binding is constructed. Our data demonstrate that the LIPHAK-disease-associated Ltv1 mutation leads to global defects in head assembly, which are explained by direct binding of Ltv1 to 5 out of 15 RPs, and indirect effects that affect 4 additional RPs. These indirect effects are mediated by conformational transitions in the nascent subunit that are regulated by Ltv1. Mechanistically, Ltv1 aids the recruitment of some RPs via direct protein-protein interactions, but surprisingly also delays the recruitment of other RPs. Delayed binding of key RPs also delays the acquisition of RNA structure that is stabilized by these proteins. Finally, our data also indicate direct roles for Ltv1 in chaperoning the folding of a key rRNA structural element, the three-helix junction j34-35-38. Thus, Ltv1 plays critical roles in organizing the order of both RP binding to rRNA and rRNA folding, thereby enabling efficient 40S subunit assembly.

molecular biology↗