what a difference a dalton makes: bacterial a difference a dalton makes: bacterial virulence factors

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  • What a Difference a Dalton Makes: Bacterial Virulence FactorsModulate Eukaryotic Host Cell Signaling Systems via Deamidation

    Erica J. Washington,a Mark J. Banfield,f Jeffery L. Dangla,b,c,d,e

    Department of Biology,a Howard Hughes Medical Institute,b Curriculum in Genetics and Molecular Biology,c Department of Microbiology and Immunology,d and CarolinaCenter for Genome Sciences,e University of North Carolina, Chapel Hill, North Carolina, USA; Department of Biological Chemistry, John Innes Centre, Norwich ResearchPark, Norwich, United Kingdomf

    SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .527INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .527CYTOTOXIC NECROTIZING FACTOR TOXINS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .528

    Cytotoxic Necrotizing Factor Toxins Deamidate Rho GTPases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .528The C Terminus of CNF1 Forms a Single Compact Catalytic Domain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .529

    BURKHOLDERIA LETHAL FACTOR 1 INHIBITS ACTIVITY OF TRANSLATION FACTOR eIF4A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .529VIBRIO PARAHAEMOLYTICUS TYPE III EFFECTOR VopC DEAMIDATES SMALL GTPases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .530PASTEURELLA MULTOCIDA TOXIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .530

    PMT Is a Multidomain Toxin, with Catalytic Activity Located at the C Terminus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .530PMT Deamidation of Heterotrimeric G Protein Families Affects Several Downstream Signaling Events. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .531

    CYCLE-INHIBITING FACTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .531Members of the Cif Family of Deamidases Are Found in Many Bacterial Pathogens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .531Deamidation of NEDD8 by Cif Leads to Disruption of the Ubiquitin-Proteasome System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .532Multiple Structures Reveal that Cif Proteins Are Members of the Papain-Like Superfamily. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .533Cif Deamidases Were the First To Be Cocrystallized with Their Substrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .533

    OspI INHIBITS HOST IMMUNE RESPONSES BY DEAMIDATING AN E2-CONJUGATING ENZYME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .534Deamidation of Ubc13 by OspI Inhibits Host Inflammatory Responses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .534OspI Forms a Papain-Like Catalytic Pocket That Rearranges upon Binding Ubc13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .535

    CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .535ACKNOWLEDGMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .536REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .536AUTHOR BIOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .539

    SUMMARY

    Pathogenic bacteria commonly deploy enzymes to promote viru-lence. These enzymes can modulate the functions of host cell tar-gets. While the actions of some enzymes can be very obvious (e.g.,digesting plant cell walls), others have more subtle activities. De-pending on the lifestyle of the bacteria, these subtle modificationscan be crucially important for pathogenesis. In particular, if bac-teria rely on a living host, subtle mechanisms to alter host cellularfunction are likely to dominate. Several bacterial virulence factorshave evolved to use enzymatic deamidation as a subtle posttrans-lational mechanism to modify the functions of host protein tar-gets. Deamidation is the irreversible conversion of the amino acidsglutamine and asparagine to glutamic acid and aspartic acid, re-spectively. Interestingly, all currently characterized bacterialdeamidases affect the function of the target protein by modifyinga single glutamine residue in the sequence. Deamidation of targethost proteins can disrupt host signaling and downstream pro-cesses by either activating or inactivating the target. Despite thesubtlety of this modification, it has been shown to cause dramatic,context-dependent effects on host cells. Several crystal structuresof bacterial deamidases have been solved. All are members of thepapain-like superfamily and display a cysteine-based catalytictriad. However, these proteins form distinct structural subfamiliesand feature combinations of modular domains of various func-tions. Based on the diverse pathogens that use deamidation as amechanism to promote virulence and the recent identification of

    multiple deamidases, it is clear that this enzymatic activity isemerging as an important and widespread feature in bacterialpathogenesis.

    INTRODUCTION

    Many bacterial pathogens use diverse suites of virulence fac-tors to contribute to pathogenicity. These virulence factorsinclude toxins and type III effectors, which are proteins injectedinto host cells via specialized type III secretion systems. Effectorsoften modify eukaryotic host target proteins with posttransla-tional modifications that alter normal cellular function. Com-monly described posttranslational modifications utilized by effec-tors include ubiquitination, acetylation, and AMPylation (13).Recently, enzymatic deamidation has emerged as a common post-translational modification utilized by a broad range of bacterialpathogens of both plants and animals to alter the functions of hostproteins. Deamidation is the replacement of an amide group witha carboxylate group (Fig. 1). Therefore, it converts glutamine andasparagine to glutamic acid and aspartic acid, respectively. Thisirreversible amino acid conversion results in an increase of ap-proximately 1 Da in the mass of the target protein, an increase in

    Address correspondence to Jeffery L. Dangl, dangl@email.unc.edu.

    Copyright 2013, American Society for Microbiology. All Rights Reserved.

    doi:10.1128/MMBR.00013-13

    September 2013 Volume 77 Number 3 Microbiology and Molecular Biology Reviews p. 527539 mmbr.asm.org 527

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    http://dx.doi.org/10.1128/MMBR.00013-13http://mmbr.asm.orghttp://mmbr.asm.org/
  • the negative charge of the target protein, and the release of ammo-nia. Nonspecific deamidation can occur spontaneously as pro-teins age and are degraded (4). In contrast, specific enzymaticdeamidation can regulate normal cellular functions, such as che-motaxis and protein turnover in prokaryotes, or disrupt eukary-otic host cell function during infection (5, 6). Here we focus ondeamidases that contribute to bacterial virulence.

    The topic of this review is the six currently known families ofbacterial virulence factors that use deamidation to modulate hostfunctions during infection (Table 1). Cytotoxic necrotizing fac-tors (CNFs) are