Molina, J. A. | Search bioRxiv

bioRxiv2021

A poxvirus decapping enzyme localizes to mitochondria to regulate RNA metabolism and translation, and promote viral replication

Decapping enzymes remove the 5-cap of eukaryotic mRNA, leading to accelerated RNA decay. They are critical in regulating RNA homeostasis and play essential roles in many cellular and life processes. They are encoded in many organisms and viruses, including vaccinia virus, which was used as the vaccine to eradicate smallpox. Vaccinia virus encodes two decapping enzymes, D9 and D10, that are necessary for efficient viral replication and pathogenesis. However, the underlying molecular mechanism regulating vaccinia decapping enzymes function is still largely elusive. Here we demonstrated that vaccinia D10 localized almost exclusively to mitochondria that are highly mobile cellular organelles, providing an innovative mechanism to concentrate D10 locally and mobilize it to efficiently decap mRNAs. As mitochondria were barely present in "viral factories," where viral transcripts are produced, suggesting that mitochondrial localization provides a spatial mechanism to preferentially decap cellular mRNAs over viral mRNAs. We identified three amino acids responsible for D10s mitochondrial localization. Loss of mitochondrial localization significantly impaired viral replication, reduced D10s ability to resolve RNA 5-cap aggregation during infection, diminished D10s gene expression shutoff and mRNA translation promotion abilities. ImportanceDecapping enzymes comprise many members from various organisms ranging from plants, animals, and viruses. The mechanisms regulating their functions vary and are still largely unknown. Our study provides the first mitochondria-localized decapping enzyme, D10, encoded by vaccinia virus that was used as the vaccine to eradicate smallpox. Loss of mitochondrial localization significantly impaired viral replication and D10s gene expression shutoff and mRNA translation promotion ability. Mitochondrial localization is a spatial mechanism to concentrate D10 locally and mobilize it to efficiently and preferentially target cellular mRNAs for decapping and promote viral mRNA translation. Our results have broad impacts on understanding the functions and mechanisms of decapping enzymes.

microbiology↗

bioRxiv2019

Differential local stability governs the metamorphic fold-switch of bacterial virulence factor RfaH

A regulatory factor RfaH, present in many Gram-negative bacterial pathogens, is required for transcription and translation of long operons encoding virulence determinants. Escherichia coli RfaH action is controlled by a unique large-scale structural rearrangement triggered by recruitment to transcription elongation complexes through a specific DNA sequence within these operons. Upon recruitment, the C-terminal domain of this two-domain protein refolds from an -hairpin, which is bound to the RNA polymerase binding site within the N-terminal domain of RfaH, into an unbound {beta}-barrel that interacts with the ribosome to enable translation. Although structures of the autoinhibited (-hairpin) and active ({beta}-barrel) states and plausible refolding pathways have been reported, how this reversible switch is encoded within RfaH sequence and structure is poorly understood. Here, we combined hydrogen-deuterium exchange measurements by mass spectrometry and nuclear magnetic resonance with molecular dynamics to evaluate the differential local stability between both RfaH folds. Deuteron incorporation reveals that the tip of the C-terminal hairpin (residues 125-145) is stably folded in the autoinhibited state ([~]20% deuteron incorporation), while the rest of this domain is highly flexible (>40% deuteron incorporation) and its flexibility only decreases in the {beta}-folded state. Computationally-predicted {Delta}Gs agree with these results by displaying similar anisotropic stability within the tip of the -hairpin and on neighboring N-terminal domain residues. Remarkably, the {beta}-folded state shows comparable stability to non-metamorphic homologs. Our findings provide information critical for understanding the metamorphic behavior of RfaH and other chameleon proteins, and for devising targeted strategies to combat bacterial diseases.\n\nSignificanceInfections caused by Gram-negative bacteria are a worldwide health threat due to rapid acquisition of antibiotic resistance. RfaH, a protein essential for virulence in several Gram-negative pathogens, undergoes a large-scale structural rearrangement in which one RfaH domain completely refolds. Refolding transforms RfaH from an inactive state that restricts RfaH recruitment to a few target genes into an active state that binds to, and couples, transcription and translation machineries to elicit dramatic activation of gene expression. However, the molecular basis of this unique conformational change is poorly understood. Here, we combine molecular dynamics and structural biology to unveil the hotspots that differentially stabilize both states of RfaH. Our findings provide novel insights that will guide design of inhibitors blocking RfaH action.

biophysics↗