Yersinia Protein Kinase Research Articles

Yersinia protein kinase A phosphorylates vasodilator-stimulated phosphoprotein to modify the host cytoskeleton.

Pathogenic Yersinia species evolved a type III secretion system that injects a set of effectors into the host cell cytosol to promote infection. One of these effectors, Yersinia protein kinase A (YpkA), is a multidomain effector that harbours a Ser/Thr kinase domain and a guanine dissociation inhibitor (GDI) domain. The intercellular targets of the kinase and GDI domains of YpkA were identified to be Gαq and the small GTPases RhoA and Rac1, respectively, which synergistically induce cytotoxic effects on infected cells. In this study, we demonstrate that vasodilator-stimulated phosphoprotein (VASP), which is critical for regulation of actin assembly, cell adhesion and motility, is a direct substrate of YpkA kinase activity. Ectopic co-expression of YpkA and VASP in HEK293T cells leads to the phosphorylation of VASP at S157, and YpkA kinase activity is essential for VASP phosphorylation at this site. Moreover, YpkA directly phosphorylates VASP in in vitro kinase assay. YpkA-mediated VASP phosphorylation significantly inhibits actin polymerization and promotes the disruption of actin cytoskeleton, which inhibits the phagocytosis. Taken together, our study found a novel molecular mechanism used by YpkA to disrupt cytoskeleton dynamics, thereby promoting the anti-phagocytosis ability of pathogenic Yersiniae.

Regulation of Yersinia Protein Kinase A (YpkA) Kinase Activity by Multisite Autophosphorylation and Identification of an N-terminal Substrate-binding Domain in YpkA

The serine/threonine protein kinase YpkA is an essential virulence factor produced by pathogenic Yersinia species. YpkA is delivered into host mammalian cells via a type III secretion system and localizes to the inner side of the plasma membrane. We have previously shown that YpkA binds to and phosphorylates the α subunit of the heterotrimeric G protein complex, Gαq, resulting in inhibition of Gαq signaling. To identify residues in YpkA involved in substrate binding activity we generated GFP-YpkA N-terminal deletion mutants and performed coimmunoprecipitation experiments. We located a substrate-binding domain on amino acids 40-49 of YpkA, which lies within the previously identified membrane localization domain on YpkA. Deletion of amino acids 40-49 on YpkA interfered with substrate binding, substrate phosphorylation and substrate inhibition. Autophosphorylation regulates the kinase activity of YpkA. To dissect the mechanism by which YpkA transmits signals, we performed nano liquid chromatography coupled to tandem mass spectrometry to map in vivo phosphorylation sites. Multiple serine phosphorylation sites were identified in the secretion/translocation region, kinase domain, and C-terminal region of YpkA. Using site-directed mutagenesis we generated multiple YpkA constructs harboring specific serine to alanine point mutations. Our results demonstrate that multiple autophosphorylation sites within the N terminus regulate YpkA kinase activation, whereas mutation of serine to alanine within the C terminus of YpkA had no effect on kinase activity. YpkA autophosphorylation on multiple sites may be a strategy used by pathogenic Yersinia to prevent inactivation of this important virulence protein by host proteins.

ANTIGENIC PROFILING OF YERSINIA PESTIS INFECTION IN THE WYOMING COYOTE (CANIS LATRANS)

Although Yersinia pestis is classified as a "high-virulence" pathogen, some host species are variably susceptible to disease. Coyotes (Canis latrans) exhibit mild, if any, symptoms during infection, but antibody production occurs postinfection. This immune response has been reported to be against the F1 capsule, although little subsequent characterization has been conducted. To further define the nature of coyote humoral immunity to plague, qualitative serology was conducted to assess the antiplague antibody repertoire. Humoral responses to six plasmid-encoded Y. pestis virulence factors were first examined. Of 20 individual immune coyotes, 90% were reactive to at least one other antigen in the panel other than F1. The frequency of reactivity to low calcium response plasmid (pLcr)-encoded Yersinia protein kinase A (YpkA) and Yersinia outer protein D (YopD) was significantly greater than that previously observed in a murine model for plague. Additionally, both V antigen and plasminogen activator were reactive with over half of the serum samples tested. Reactivity to F1 was markedly less frequent in coyotes (35%). Twenty previously tested antibody-negative samples were also examined. While the majority were negative across the panel, 15% were positive for 1-3 non-F1 antigens. In vivo-induced antigen technology employed to identify novel chromosomal genes of Y. pestis that are up-regulated during infection resulted in the identification of five proteins, including a flagellar component (FliP) that was uniquely reactive with the coyote serum compared with immune serum from two other host species. Collectively, these data suggest that humoral immunity to pLcr-encoded antigens and the pesticin plasmid (pPst)-encoded Pla antigen may be relevant to plague resistance in coyotes. The serologic profile of Y. pestis chromosomal antigens up-regulated in vivo specific to C. latrans may provide insight into the differences in the pathogen-host responses during Y. pestis infection.

The Activities of the Yersinia Protein Kinase A (YpkA) and Outer Protein J (YopJ) Virulence Factors Converge on an eIF2α Kinase

The Yersinia protein kinase A (YpkA) and outer protein J (YopJ) are co-expressed from a single transcript and are injected directly into eukaryotic cells by the plague bacterium Yersinia pestis. When overexpressed in vertebrate or yeast cells, YpkA disrupts the actin-based cytoskeletal system by an unknown mechanism, whereas YopJ obstructs inductive chemokine expression by inhibiting MAPK and NF-kappaB signaling. Previously, we showed that the fission yeast Schizosaccharomyces pombe was sensitive to the kinase activity of YpkA. Here, we screened yeast for cellular processes important for YpkA activity and found that the eIF2alpha kinases mollify the toxicity imparted by the kinase activity of YpkA. Specifically, strains lacking the eIF2alpha kinase Hri2 were particularly sensitive to YpkA. Unexpectedly, the activity of YopJ, which conferred a phenotype consistent with its inhibitory effect on MAPK signaling, was also found to be dependent on Hri2. When expressed in S. pombe, YopJ sensitized cells to osmotic and oxidative stresses through a Hri2-dependent mechanism. However, when co-expressed with YpkA, YopJ protected cells from YpkA-mediated toxicity, and this protection was entirely dependent on Hri2. In contrast, YopJ did not confer protection against the toxic effects of the Yersinia virulence factor YopE. These findings are the first to functionally link YpkA and YopJ and suggest that eIF2alpha kinases, which are critically important in antiviral defenses and protection against environmental stresses, also play a role in bacterial virulence.

The elusive activity of the Yersinia protein kinase A kinase domain is revealed

Yersinia spp. pathogens use their type III secretion system to translocate effectors that manipulate host signaling pathways during infection. Although molecular targets for five of the six known Yersinia effectors are known, the target for the serine/threonine kinase domain of Yersinia protein kinase A (YpkA) has remained elusive. Recently, Navarro et al. (2007) demonstrated that YpkA phosphorylates Galphaq, and inhibits Galphaq-mediated signaling. Inhibition by YpkA could contribute to one of the most documented symptoms of Yersinia pestis infection, extensive bleeding.

Targeting Plague Virulence Factors: A Combined Machine Learning Method and Multiple Conformational Virtual Screening for the Discovery of Yersinia Protein Kinase A Inhibitors

Yersinia spp. is currently an antibiotic resistance concern and a re-emerging disease. The essential virulence factor Yersinia protein kinase A (YpkA) contains a Ser/Thr kinase domain whose activity modulates pathogenicity. Here, we present an approach integrating a machine learning method, homology modeling, and multiple conformational high-throughput docking for the discovery of YpkA inhibitors. These first reported inhibitors of YpkA may facilitate studies of the pathogenic mechanism of YpkA and serve as a starting point for development of anti-plague drugs.

Virulent Protein Kinase A

The Yersinia Gram-negative bacteria are pathogenic to humans causing such diseases as bubonic plague. Through the action of a type III protein secretion system, Yersinia injects bacterial proteins necessary to subvert the host cell's normal processes and to promote bacterial survival and replication. Navarro et al . report that, in addition to the previously known inhibitory activity toward guanosine triphosphatases (GTPases) Rac1 and RhoA, Yersinia protein kinase A (YpkA) also inhibits G protein (heterotrimeric guanine nucleotide-binding protein) signaling by phosphorylation of the Gα subunit. The actin cytoskeleton disruption in cells expressing either the full-length YpkA or a C-terminal fragment was prevented if the cells also expressed a constitutively active form of RhoA, suggesting that YpkA acted upstream of this GTPase. G protein-coupled receptors can stimulate reorganization of the actin cytoskeleton through the activation of RhoA. Exposure of cells transfected with the muscarinic receptor to carbachol stimulated Gα q signaling and promoted the formation of stress fibers. Transfection of YpkA, but not a catalytically inactive version, inhibited this Gα q -induced reorganization of the cytoskeleton. YpkA coimmunoprecipitated with Gα q (both GDP-bound and GTP-bound forms) and Gα q was phosphorylated when immunoprecipitated from cells expressing catalytically active YpkA. The phosphorylation site was mapped to a serine within the consensus guanine nucleotide-binding loop by liquid chromatography tandem mass spectrometry. Phosphorylation of this residue appeared to disrupt activation of the G protein as substitution of the serine with aspartate (to mimic phosphorylation) prevented GTP loading. Not only was signaling from the muscarinic receptor to the cytoskeleton blocked by expression of YpkA, so was nuclear translocation of tubby, a transcriptional regulator released from the plasma membrane in response to Gα q -mediated stimulation of phospholipase C. In cells infected with Yersinia , both wild-type and catalytically inactive YpkA disrupted the actin cytoskeleton, presumably because the protein contains two functional domains that can inhibit the actin cytoskeleton: the C-terminal guanine nucleotide dissociation inhibitor region that directly targets RhoA and the serine-threonine kinase activity of the N-terminal region that inhibits G protein signaling to the cytoskeleton. L. Navarro, A. Koller, R. Nordfelth, H. Wolf-Watz, S. Taylor, J. E. Dixon, Identification of a molecular target for the Yersinia protein kinase A. Mol. Cell 26 , 465-477 (2007). [PubMed]

Identification of a Molecular Target for the Yersinia Protein Kinase A

Pathogenic bacteria of the genus Yersinia employ a type III secretion system to inject bacterial effector proteins directly into the host cytosol. One of these effectors, the Yersinia serine/threonine protein kinase YpkA, is an essential virulence determinant involved in host actin cytoskeletal rearrangements and in inhibition of phagocytosis. Here we report that YpkA inhibits multiple Galphaq signaling pathways. The kinase activity of YpkA is required for Galphaq inhibition. YpkA phosphorylates Ser47, a key residue located in the highly conserved diphosphate binding loop of the GTPase fold of Galphaq. YpkA-mediated phosphorylation of Ser47 impairs guanine nucleotide binding by Galphaq. Y. pseudotuberculosis expressing wild-type YpkA, but not a catalytically inactive YpkA mutant, interferes with Galphaq-mediated signaling pathways. Identification of a YpkA-mediated phosphorylation site in Galphaq sheds light on the contribution of the kinase activity of YpkA to Yersinia pathogenesis.

Yersinia Protein Kinase YopO Is Activated by A Novel G-actin Binding Process

Pathogenic bacteria of the genus Yersinia employ a type III secretion system to inject effector proteins (Yops) into host cells. The Yops down-regulate host cell functions through unique biochemical activities. YopO, a serine/threonine kinase required for Yersinia virulence, is activated by host cell actin via an unknown process. Here we show that YopO kinase is activated by formation of a 1:1 complex with monomeric (G) actin but is unresponsive to filamentous (F) actin. Two separate G-actin binding sites, one in the N-terminal kinase region (amino acids 89-440) and one in the C-terminal guanine nucleotide dissociation inhibitor-like region (amino acids 441-729) of YopO, were identified. Actin binding to both of these sites was necessary for effective autophosphorylation of YopO on amino acids Ser-90 and Ser-95. A S90A/S95A YopO mutant was strongly reduced in substrate phosphorylation, suggesting that autophosphorylation activates YopO kinase activity. In cells the kinase activity of YopO regulated rounding/arborization and was specifically required for inhibition of Yersinia YadA-dependent phagocytosis. Thus, YopO kinase is activated by a novel G-actin binding process, and this appears to be crucial for its anti-host cell functions.

Yersinia Virulence Depends on Mimicry of Host Rho-Family Nucleotide Dissociation Inhibitors

Yersinia spp. cause gastroenteritis and the plague, representing historically devastating pathogens that are currently an important biodefense and antibiotic resistance concern. A critical virulence determinant is the Yersinia protein kinase A, or YpkA, a multidomain protein that disrupts the eukaryotic actin cytoskeleton. Here we solve the crystal structure of a YpkA-Rac1 complex and find that YpkA possesses a Rac1 binding domain that mimics host guanidine nucleotide dissociation inhibitors (GDIs) of the Rho GTPases. YpkA inhibits nucleotide exchange in Rac1 and RhoA, and mutations that disrupt the YpkA-GTPase interface abolish this activity in vitro and impair in vivo YpkA-induced cytoskeletal disruption. In cell culture experiments, the kinase and the GDI domains of YpkA act synergistically to promote cytoskeletal disruption, and a Y. pseudotuberculosis mutant lacking YpkA GDI activity shows attenuated virulence in a mouse infection assay. We conclude that virulence in Yersinia depends strongly upon mimicry of host GDI proteins by YpkA.

The Ser/Thr kinase activity of the Yersinia protein kinase A (YpkA) is necessary for full virulence in the mouse, mollifying phagocytes, and disrupting the eukaryotic cytoskeleton

The Yersinia protein kinase A (YpkA) is injected into host cells by the yersinial type three secretion system (TTSS). YpkA is widely believed to function within the host cell based on the fact that its kinase domain is clearly homologous to eukaryotic Ser/Thr kinases and that its enzymatic activity, when assayed in vitro, is dependent on eukaryotic-derived host factors. Whether this activity is required for virulence has not been addressed. Here, we report that a Yersinia pseudotuberculosis strain expressing a kinase-inactive YpkA D270A variant is greatly attenuated in the mouse model of infection compared to the isogenic wild-type strain. The ypkA D270A mutant strain was likewise attenuated in a cell culture infection assay indicating that the kinase activity of YpkA enhances the viability of host cell-associated bacteria. To begin to understand what cellular activities are targeted, we expressed YpkA and its variants in two different yeast model systems. In agreement with previous studies, we found that when rapidly induced and expressed at high levels in Saccharomyces cerevisiae, YpkA-mediated toxicity occurred extremely swiftly. Under these conditions toxicity was dependent on the structurally distinct GTPase-binding domain of YpkA and was entirely independent of its kinase activity. Therefore, to probe for kinase-dependent effects we expressed YpkA and its kinase-inactive variant at comparatively moderate levels in the fission yeast Schizosaccharomyces pombe. S. pombe is particularly well suited for actin cytoskeletal studies due to its easily quantifiable, well defined pattern of actin localization. S. pombe transformed with a wild-type YpkA-encoding plasmid displayed a pronounced actin mislocalization phenotype, the severity of which was directly proportional to the level of YpkA expressed in the cell. In cells expressing the kinase-inactive YpkA variant, the degree of actin mislocalization was reduced, but not entirely abrogated, suggesting that YpkA affects the eukaryotic cytoskeleton through kinase-dependent and kinase-independent mechanisms. Collectively, our yeast-derived results show how critical expression levels and exposure periods are for assaying virulence factor activities in heterologous model systems. More generally, our finding that the ‘eukaryotic-like’ kinase domain of YpkA is important for virulence illustrates how a bacterium can utilize a host-like factor or activity in order to enhance its survival following host cell contact.

Identification of otubain 1 as a novel substrate for the Yersinia protein kinase using chemical genetics and mass spectrometry

Yersinia encodes a protein kinase, YpkA, which disrupts the actin cytoskeleton. Using an approach termed chemical genetics, we identified a 36-kDa substrate for YpkA in both J774 lysates and bovine brain cytosol. Mass spectrometry analysis identified this substrate as FLJ20113, an open reading frame that corresponds to otubain 1, a deubiquitinating enzyme implicated in immune cell clonal anergy. We demonstrate that otubain 1 is phosphorylated by YpkA in vitro and interacts with YpkA and actin in vivo. Identification of otubain 1 as a YpkA substrate suggests that regulation of immune cell anergy may be a survival mechanism for Yersinia.

Eukaryotic Targets of a Bacterial Protein Kinase Virulence Factor.

INTRODUCTION. Several animaland plant-interacting Gram-negative bacteria possess the socalled type III secretion system or TTSS, which functions to inject proteins (or ‘effectors’) directly into eukaryotic cells[1]. TTSS effectors play important roles in a variety of host-microbe interactions including Rhizobium-mediated root nodulation, plant hypersensitivity reactions, and in animals, modulating immune responses. The pathogenic yersiniae (Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica) inject five TTSS effectors all of which are required for full virulence in the mouse model. As might be expected since they function within host cells, Yersinia’s TTSS effectors possess clear eukaryotic-like protein domains or motifs. One of these effectors, the Yersinia protein kinase A (YpkA), contains the canonical 11 subdomains (I-XI) characteristic of eukaryotic ser/thr protein kinases with a highly conserved catalytic core sequence. In addition to the amino-terminally located kinase domain, YpkA, also contains in its carboxyl-terminal region sequences that resemble eukaryotic RhoA-binding domains.

The Yersinia Protein Kinase A Is a Host Factor Inducible RhoA/Rac-binding Virulence Factor

The pathogenic yersiniae inject proteins directly into eukaryotic cells that interfere with a number of cellular processes including phagocytosis and inflammatory-associated host responses. One of these injected proteins, the Yersinia protein kinase A (YpkA), has previously been shown to affect the morphology of cultured eukaryotic cells as well as to localize to the plasma membrane following its injection into HeLa cells. Here it is shown that these activities are mediated by separable domains of YpkA. The amino terminus, which contains the kinase domain, is sufficient to localize YpkA to the plasma membrane while the carboxyl terminus of YpkA is required for YpkAs morphological effects. YpkAs carboxyl-terminal region was found to affect the levels of actin-containing stress fibers as well as block the activation of the GTPase RhoA in Yersinia-infected cells. We show that the carboxyl-terminal region of YpkA, which contains sequences that bear similarity to the RhoA-binding domains of several eukaryotic RhoA-binding kinases, directly interacts with RhoA as well as Rac (but not Cdc42) and displays a slight but measurable binding preference for the GDP-bound form of RhoA. Surprisingly, YpkA binding to RhoA(GDP) affected neither the intrinsic nor guanine nucleotide exchange factor-mediated GDP/GTP exchange reaction suggesting that YpkA controls activated RhoA levels by a mechanism other than by simply blocking guanine nucleotide exchange factor activity. We go on to show that YpkAs kinase activity is neither dependent on nor promoted by its interaction with RhoA and Rac but is, however, entirely dependent on heat-sensitive eukaryotic factors present in HeLa cell extracts and fetal calf serum. Collectively, our data show that YpkA possesses both similarities and differences with the eukaryotic RhoA/Rac-binding kinases and suggest that the yersiniae utilize the Rho GTPases for unique activities during their interaction with eukaryotic cells.