Background:The Fic domain mediates AMPylation and is highly conserved in various species. Results: BiP is identified as a substrate of Fic, and its AMPylation state is modulated by ER stress. Conclusion: AMPylation of BiP presents a regulatory mechanism for cells to achieve ER homeostasis. Significance: BiP is the first known substrate for AMPylation by a eukaryotic Fic protein.

The initial binding of bacteria to host cells is crucial to the delivery of virulence factors and thus is a key determinant of the pathogen's success. We report a multivalent adhesion molecule (MAM) that enables a wide range of Gram-negative pathogens to establish high-affinity binding to host cells during the early stages of infection. MAM7 binds to the host by engaging in both protein-protein (with fibronectin) and protein-lipid (with phosphatidic acid) interactions with the host cell membrane. We find that MAM7 expression on the outer membrane of a Gram-negative pathogen is necessary for virulence in a nematode infection model and for efficient killing of cultured mammalian host cells. Expression of MAM7 on nonpathogenic strains produced a tool that can be used to impede infection by Gram-negative bacterial pathogens. Targeting or exploiting MAM7 might prove to be important in combating Gram-negative bacterial infections.adhesin | microbiology | bacterial attachment B acterial pathogens have a large repertoire of virulence factors that target and manipulate the host cellular machinery to enable infection. Delivery of effector proteins to the host cytosol by type III, type IV, and type VI secretion systems, as well as delivery of extracellular toxins, is a common strategy used by bacterial pathogens to abrogate the host immune response and alter cellular pathways to the pathogen's advantage (1, 2). Because the secretion of effector and toxin proteins is contact-dependent, the bacteria need to establish tight binding to the host to successfully start an infection. We hypothesize that a common strategy exists across species enabling the pathogen to establish strong initial host binding that is complemented by other species-specific adhesion factors for efficient activation and secretion of virulence factors and toxins. During infection, a variety of adhesion factors are expressed by pathogens to facilitate host-pathogen interactions (3-5). Many of these adhesins are induced during infection and thus likely would not be involved in the initial adhesion of the bacterial pathogen with the host cell.Using bioinformatics, we searched the genome of Vibrio parahaemolyticus, a Gram-negative bacterium that occurs in marine and estuarine environments and can cause shellfish-borne food poisoning, for a constitutively expressed protein that might be involved in the initial binding of bacteria to a host cell (6). We discovered a predicted outer membrane molecule, multivalent adhesion molecule (MAM), which includes a putative transmembrane motif followed by six (MAM6) or seven (MAM7) mammalian cell entry (mce) domains (Fig. 1A and Fig. S1A Unexpectedly, we found that MAM6 or MAM7 is encoded in a wide range of Gram-negative animal pathogens, but not in Grampositive or plant pathogenic bacteria (Fig. 1A and Figs. S1B and S2). In contrast, proteins containing a single mce domain are widespread (Fig. 1A). In Mycobacterium spp. and some Grampositive bacteria, including Rhodococcus spp. and Streptomyces spp., the mce domain occurs ...

Bacterial pathogens interact with host membranes to trigger a wide range of cellular processes during the course of infection. These processes include alterations to the dynamics between the plasma membrane and the actin cytoskeleton, and subversion of the membrane-associated pathways involved in vesicle trafficking. Such changes facilitate the entry and replication of the pathogen, and prevent its phagocytosis and degradation. In this Review, we describe the manipulation of host membranes by numerous bacterial effectors that target phosphoinositide metabolism, GTPase signalling and autophagy.

Fic domains can catalyze the addition of adenosine monophosphate to target proteins. To date, the function of Fic domain proteins in eukaryotic physiology remains unknown. We generated genetic models of the single Drosophila Fic domain–containing protein, Fic. Flies lacking Fic were viable and fertile, but blind. Photoreceptor cells depolarized normally following light stimulation, but failed to activate postsynaptic neurons, as indicated by the loss of ON transients in electroretinograms, consistent with a neurotransmission defect. Functional rescue of neurotransmission required expression of enzymatically active Fic on capitate projections of glia cells, but not neurons, supporting a role in the recycling of the visual neurotransmitter histamine. Histamine levels were reduced in the lamina of Fic null flies, and dietary histamine partially restored ON transients. These findings establish a previously unknown regulatory mechanism in visual neurotransmission and provide, to the best of our knowledge, the first evidence for a role of glial capitate projections in neurotransmitter recycling.

Vibrio parahaemolyticus, a Gram-negative marine bacterial pathogen, is emerging as a major cause of food-borne illnesses worldwide due to the consumption of raw seafood leading to diseases including gastroenteritis, wound infection, and septicemia. The bacteria utilize toxins and type III secretion system (T3SS) to trigger virulence. T3SS is a multi-subunit needle-like apparatus used to deliver bacterial proteins, termed effectors, into the host cytoplasm which then target various eukaryotic signaling pathways. V. parahaemolyticus carries two T3SSs in each of its two chromosomes, named T3SS1 and T3SS2, both of which play crucial yet distinct roles during infection: T3SS1 causes cytotoxicity whereas T3SS2 is mainly associated with enterotoxicity. Each T3SS secretes a unique set of effectors that contribute to virulence by acting on different host targets and serving different functions. Emerging studies on T3SS2 of V. parahaemolyticus, reveal its regulation, translocation, discovery, characterization of its effectors, and development of animal models to understand the enterotoxicity. This review on recent findings for T3SS2 of V. parahaemolyticus highlights a novel mechanism of invasion that appears to be conserved by other marine bacteria.

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AMPylation, a posttranslational modification in which adenosine monophosphate (AMP) is added to hydroxyl side chains of protein substrates, is employed by many bacterial pathogens to subvert host signaling pathways during infection. The Legionella pneumophila effector protein SidM is a multifunctional enzyme that targets the guanosine triphosphatase (GTPase) Rab1 to manipulate intracellular vesicular trafficking in the host cell. SidM recruits Rab1 to the membranes of Legionella-containing vacuoles and activates Rab1 through its guanine nucleotide exchange factor activity. SidM then AMPylates Rab1, converting it into a constitutively active form that cannot be accessed by LepB, a GTPase-activating protein that is secreted by L. pneumophila. However, the molecular event that eventually leads to Rab1 inactivation and subsequent removal from Legionella-containing vacuoles has remained unknown. New evidence has identified SidD as a de-AMPylase that removes AMP from Rab1, which enables its inactivation by LepB later during the infection process. This finding demonstrates a complete pathway of reversible modifications regulated by specific bacterial enzymes to modulate host membrane trafficking.