Biology subjects

Darwin, K. H.

Publications and source records attributed to Darwin, K. H..

3 recordsLinked to original sources

bioRxiv2018

Interleukin-1 receptor antagonist mediates type I interferon-driven susceptibility to Mycobacterium tuberculosis

The bacterium Mycobacterium tuberculosis (Mtb) causes tuberculosis (TB) and is responsible for more human mortality than any other single pathogen1. Although ~1.7 billion people are infected with Mtb2, most infections are asymptomatic. Progression to active disease occurs in ~10% of infected individuals and is predicted by an elevated type I interferon (IFN) response3-8. Type I IFNs are vital for antiviral immunity, but whether or how they mediate susceptibility to Mtb has been difficult to study, in part because the standard C57BL/6 (B6) mouse model does not recapitulate the IFN-driven disease that appears to occur in humans3-5,8. Here we examined B6. Sst1S congenic mice that carry the C3H \"sensitive\" allele of the Sst1 locus that renders them highly susceptible to Mtb infections9,10. We found that B6.Sst1S mice exhibit markedly increased type I IFN signaling, and that type I IFNs were required for the enhanced susceptibility of B6. Sst1S mice to Mtb. Type I IFNs affect the expression of hundreds of genes, several of which have previously been implicated in susceptibility to bacterial infections11,12. Nevertheless, we found that heterozygous deficiency in just a single IFN target gene, IL-1 receptor antagonist (IL-1Ra), is sufficient to reverse IFN-driven susceptibility to Mtb. As even a partial reduction in IL-1Ra levels led to significant protection, we hypothesized that IL-1Ra may be a plausible target for host-directed anti-TB therapy. Indeed, antibody-mediated neutralization of IL-1Ra provided therapeutic benefit to Mtb-infected B6. Sst1S mice. Our results illustrate how the diversity of inbred mouse strains can be exploited to better model human TB, and demonstrate that IL-1Ra is an important mediator of type I IFN-driven susceptibility to Mtb infections in vivo.

immunology↗

bioRxiv2018

Proteasome Substrate Capture and Gate Activation by Mycobacterium tuberculosis PafE

In all domains of life, proteasomes are gated chambered proteases that require opening by activators in order to facilitate protein degradation. Twelve proteasome accessory factor E (PafE) monomers assemble into a single, dodecameric ring to promote proteolysis that is required for the full virulence of the human bacterial pathogen Mycobacterium tuberculosis. While the best characterized proteasome activators use ATP to deliver proteins into a proteasome, PafE does not require ATP. In order to understand the mechanism of PafE-mediated protein targeting and proteasome activation, we studied the interactions of PafE with native substrates, including a newly identified proteasome substrate, Rv3213c, and with proteasome core particles. We characterized the function of a highly conserved feature conserved in bacterial proteasome activator proteins: a glycine-glutamine-tyrosine-leucine or \"GQYL\" motif at their carboxyl-termini that is essential to stimulate proteolysis. Using cryo-electron microscopy, we found that the GQYL motif of PafE interacts with specific residues in the -subunits of the proteasome core particle to trigger gate opening and degradation. Finally, we found that PafE rings have 40-[A] openings lined with hydrophobic residues that form a chamber for capturing substrates prior to the onset of degradation. This result suggests PafE has a previously unrecognized chaperone activity. Collectively, our data provide new insights on the mechanistic understanding of ATP-independent proteasome degradation in bacteria.

biochemistry↗

bioRxiv2017

Cytokinin signaling alters acid-fast staining of Mycobacterium tuberculosis

It was reported the human-exclusive pathogen Mycobacterium (M.) tuberculosis secretes cytokinins, which previously had only been known as plant hormones. Cytokinins are adenine-based signaling molecules in plants that have never been shown to participate in signal transduction in other kingdoms of life. Here, we show that cytokinins induce the strong expression of the M. tuberculosis gene, Rv0077c. We found that a TetR-like transcriptional regulator, Rv0078, directly repressed expression of the Rv0077c gene. Strikingly, cytokinin-induced expression of Rv0077c resulted in a loss of acid-fast staining of M. tuberculosis. Although acid-fast staining is thought to be associated with changes in the bacterial cell envelope and virulence, Rv0077c-induced loss of acid-fastness did not affect antibiotic susceptibility or attenuate bacterial growth in mice. Collectively, these findings show cytokinins signal transcriptional changes that affect the M. tuberculosis cell envelope, and that cytokinin signaling is no longer limited to the kingdom plantae.

microbiology↗