Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title><jats:p>Virulence and persistence of the obligate intracellular parasite <jats:italic>Toxoplasma gondii</jats:italic> involve the secretion of effector proteins belonging to the family of dense granule proteins (GRAs) that act notably as modulators of the host defense mechanisms and participate in cyst wall formation. The subset of GRAs residing in the parasitophorous vacuole (PV) or exported into the host cell, undergo proteolytic cleavage in the Golgi upon the action of the aspartyl protease 5 (ASP5). In tachyzoites, ASP5 substrates play central roles in the morphology of the PV and the export of effectors across the translocon complex MYR1/2/3. Here, we used N‐terminal amine isotopic labeling of substrates to identify novel ASP5 cleavage products by comparing the N‐terminome of wild‐type and Δ<jats:italic>asp5</jats:italic> lines in tachyzoites and bradyzoites. Validated substrates reside within the PV or PVM in an ASP5‐dependent manner. Remarkably, Δ<jats:italic>asp5</jats:italic> bradyzoites are impaired in the formation of the cyst wall in vitro and exhibit a considerably reduced cyst burden in chronically infected animals. More specifically two‐photon serial tomography of infected mouse brains revealed a comparatively reduced number and size of the cysts throughout the establishment of persistence in the absence of ASP5.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Pathogenic bacteria possess a great potential of causing infectious diseases and represent a serious threat to human and animal health. Understanding the molecular basis of infection development can provide new valuable strategies for disease prevention and better control. In host‐pathogen interactions, actin‐cytoskeletal dynamics play a crucial role in the successful adherence, invasion, and intracellular motility of many intruding microbial pathogens. Cortactin, a major cellular factor that promotes actin polymerization and other functions, appears as a central regulator of host‐pathogen interactions and different human diseases including cancer development. Various important microbes have been reported to hijack cortactin signaling during infection. The primary regulation of cortactin appears to proceed via serine and/or tyrosine phosphorylation events by upstream kinases, acetylation, and interaction with various other host proteins, including the Arp2/3 complex, filamentous actin, the actin nucleation promoting factor N‐WASP, focal adhesion kinase FAK, the large GTPase dynamin‐2, the guanine nucleotide exchange factor Vav2, and the actin‐stabilizing protein CD2AP. Given that many signaling factors can affect cortactin activities, several microbes target certain unique pathways, while also sharing some common features. Here we review our current knowledge of the hallmarks of cortactin as a major target for eminent Gram‐negative and Gram‐positive bacterial pathogens in humans.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Integrative and conjugative elements (ICEs) are major drivers of horizontal gene transfer in bacteria. They mediate their own transfer from host cells (donors) to recipients and allow bacteria to acquire new phenotypes, including pathogenic and metabolic capabilities and drug resistances. <jats:italic>Streptococcus mutans</jats:italic>, a major causative agent of dental caries, contains a putative ICE, Tn<jats:italic>Smu1</jats:italic>, integrated at the 3′ end of a leucyl tRNA gene. We found that Tn<jats:italic>Smu1</jats:italic> is a functional ICE, containing all the genes necessary for ICE function. It excised from the chromosome and excision was stimulated by DNA damage. We identified the DNA junctions generated by excision of Tn<jats:italic>Smu1</jats:italic>, defined the ends of the element, and detected the extrachromosomal circle. We found that Tn<jats:italic>Smu1</jats:italic> can transfer from <jats:italic>S. mutans</jats:italic> donors to recipients when co‐cultured on solid medium. The presence of Tn<jats:italic>Smu1</jats:italic> in recipients inhibited successful acquisition of another copy and this inhibition was mediated, at least in part, by the likely transcriptional repressor encoded by the element. Using microscopy to track individual cells, we found that activation of Tn<jats:italic>Smu1</jats:italic> caused an arrest of cell growth. Our results demonstrate that Tn<jats:italic>Smu1</jats:italic> is a functional ICE that affects the biology of its host cells.</jats:p>

<jats:title>Abstract</jats:title><jats:p>The <jats:italic>alaW alaX</jats:italic> operon encodes the Ala2 tRNAs, one of the two alanine tRNA isotypes in <jats:italic>Escherichia coli</jats:italic>. Our previous RNA‐seq study showed that <jats:italic>alaW alaX</jats:italic> dicistronic RNA levels increased significantly in the absence of both RNase P and poly(A) polymerase I (PAP I), suggesting a role of polyadenylation in its stability. In this report, we show that RNase E initiates the processing of the primary <jats:italic>alaW alaX</jats:italic> precursor RNA by removing the Rho‐independent transcription terminator, which appears to be the rate limiting step in the separation and maturation of the Ala2 pre‐tRNAs by RNase P. Failure to separate the <jats:italic>alaW</jats:italic> and <jats:italic>alaX</jats:italic> pre‐tRNAs by RNase P leads to poly(A)‐mediated degradation of the dicistronic RNAs by polynucleotide phosphorylase (PNPase) and RNase R. Surprisingly, the thermosensitive RNase E encoded by the <jats:italic>rne‐1</jats:italic> allele is highly efficient in removing the terminator (&gt;99%) at the nonpermissive temperature suggesting a significant caveat in experiments using this allele. Together, our data present a comprehensive picture of the Ala2 tRNA processing pathway and demonstrate that unprocessed RNase P substrates are degraded via a poly(A) mediated decay pathway.</jats:p>

<jats:title>Abstract</jats:title><jats:p>The peptidoglycan (PG) layer of bacterial cells is essential for maintaining the cell shape and survival of cells; therefore, the synthesis of PG needs to be spatiotemporally controlled. While it is well established that PG synthesis is mediated posttranslationally through interactions between PG synthases and their cognate partners, much less is known about the transcriptional regulation of genes encoding these synthases. Based on a previous finding that the Gram‐negative bacterium <jats:italic>Shewanella oneidensis</jats:italic> lacking the prominent PG synthase exhibits impaired cell wall integrity, we performed genetic selections to isolate the suppressors. We discovered that disrupting the <jats:italic>sspA</jats:italic> gene encoding stringent starvation protein A (SspA) is sufficient to suppress compromised PG. SspA serves as a transcriptional repressor that regulates the expression of the two types of PG synthases, class A penicillin‐binding proteins and SEDS/bPBP protein complexes. SspA is an RNA polymerase‐associated protein, and its regulation involves interactions with the σ<jats:sup>70</jats:sup>‐RNAP complex and an antagonistic effect of H‐NS, a global nucleoid‐associated protein. We also present evidence that the regulation of PG synthases by SspA is conserved in <jats:italic>Escherichia coli</jats:italic>, adding a new dimension to the current understanding of PG synthesis and its regulation.</jats:p>