[Show abstract][Hide abstract] ABSTRACT: Vibrio parahaemolyticus is a Gram-negative halophilic bacterium and one of the leading causes of food-borne gastroenteritis. Its genome harbors two Type III Secretion Systems (T3SS1 and T3SS2), but only T3SS2 is required for enterotoxicity seen in animal models. Effector proteins secreted from T3SS2 have been previously shown to promote colonization of the intestinal epithelium, invasion of host cells, and destruction of the epithelial monolayer. In this study, we identify VPA1380, a T3SS2 effector protein that is toxic when expressed in yeast. Bioinformatic analyses revealed that VPA1380 is highly similar to the inositol hexakisphosphate (IP6)-inducible cysteine protease domains of several large bacterial toxins. Mutations in conserved catalytic residues and residues in the putative IP6-binding pocket abolished toxicity in yeast. Furthermore, VPA1380 was not toxic in IP6 deficient yeast cells. Therefore, our findings suggest that VPA1380 is a cysteine protease that requires IP6 as an activator.
PLoS ONE 08/2014; 9(8):e104387. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The heme-copper oxidase superfamily includes heme-copper oxidases (HCOs) in aerobic respiratory chains and nitric oxide reductases (NORs) in the denitrification pathway. The HCO/NOR catalytic subunit has a core structure consisting of 12 transmembrane helices (TMHs) arranged in three-fold rotational pseudosymmetry, with six conserved histidines for heme and metal binding. Using sensitive sequence similarity searches, we detected a number of novel HCO/NOR homologs and named them HCO Homology (HCOH) proteins. Several HCOH families possess only four TMHs that exhibit the most pronounced similarity to the last four TMHs (TMHs 9-12) of HCOs/NORs. Encoded by independent genes, four-TMH HCOH proteins represent a single evolutionary unit (EU) that relates to each of the three homologous EUs from HCO/NOR comprising TMHs 1-4, TMHs 5-8 and TMHs 9-12. Single-EU HCOH proteins could form homotrimers or heterotrimers to maintain the general structure and ligand-binding sites defined by the HCO/NOR catalytic subunit fold. The remaining HCOH families, including NnrS, have 12-TMHs and three EUs. Most three-EU HCOH proteins possess two conserved histidines and could bind a single heme. Limited experimental studies and genomic context analysis suggest that many HCOH proteins could function in the denitrification pathway and in detoxification of reactive molecules such as nitric oxide. HCO/NOR catalytic subunits exhibit remarkable structural similarity to the homotrimers of MAPEG (membrane-associated proteins in eicosanoid and glutathione metabolism) proteins. Gene duplication, fusion and fission likely play important roles in the evolution of HCOs/NORs and HCOH proteins.
[Show abstract][Hide abstract] ABSTRACT: Bacteria use diverse mechanisms to kill, manipulate, and compete with other cells. The recently discovered type VI secretion system (T6SS) is widespread in bacterial pathogens and used to deliver virulence effector proteins into target cells. Using comparative proteomics, we identified two previously unidentified T6SS effectors that contained a conserved motif. Bioinformatic analyses revealed that this N-terminal motif, named MIX (marker for type six effectors), is found in numerous polymorphic bacterial proteins that are primarily located in the T6SS genome neighborhood. We demonstrate that several MIX-containing proteins are T6SS effectors and that they are not required for T6SS activity. Thus, we propose that MIX-containing proteins are T6SS effectors. Our findings allow for the identification of numerous uncharacterized T6SS effectors that will undoubtedly lead to the discovery of new biological mechanisms.
Proceedings of the National Academy of Sciences of the United States of America. 06/2014;
[Show abstract][Hide abstract] ABSTRACT: Bacterial Type III Secretion Systems deliver effectors into host cells to manipulate cellular processes to the advantage of the pathogen. Many host targets of these effectors are found on membranes. Therefore, to identify their targets, effectors often use specialized membrane-localization domains to localize to appropriate host membranes. However, the molecular mechanisms used by many domains are unknown. Here we identify a conserved bacterial phosphoinositide-binding domain (BPD) that is found in functionally diverse Type III effectors of both plant and animal pathogens. We show that members of the BPD family functionally bind phosphoinositides and mediate localization to host membranes. Moreover, NMR studies reveal that the BPD of the newly identified Vibrio parahaemolyticus Type III effector VopR is unfolded in solution, but folds into a specific structure upon binding its ligand phosphatidylinositol-(4,5)-bisphosphate. Thus, our findings suggest a possible mechanism for promoting refolding of Type III effectors after delivery into host cells.
[Show abstract][Hide abstract] ABSTRACT: Cell surface growth factor receptors couple environmental cues to the regulation of cytoplasmic homeostatic processes, including autophagy, and aberrant activation of such receptors is a common feature of human malignancies. Here, we defined the molecular basis by which the epidermal growth factor receptor (EGFR) tyrosine kinase regulates autophagy. Active EGFR binds the autophagy protein Beclin 1, leading to its multisite tyrosine phosphorylation, enhanced binding to inhibitors, and decreased Beclin 1-associated VPS34 kinase activity. EGFR tyrosine kinase inhibitor (TKI) therapy disrupts Beclin 1 tyrosine phosphorylation and binding to its inhibitors and restores autophagy in non-small-cell lung carcinoma (NSCLC) cells with a TKI-sensitive EGFR mutation. In NSCLC tumor xenografts, the expression of a tyrosine phosphomimetic Beclin 1 mutant leads to reduced autophagy, enhanced tumor growth, tumor dedifferentiation, and resistance to TKI therapy. Thus, oncogenic receptor tyrosine kinases directly regulate the core autophagy machinery, which may contribute to tumor progression and chemoresistance.
[Show abstract][Hide abstract] ABSTRACT: The molecular mechanism of autophagy and its relationship to other lysosomal degradation pathways remain incompletely understood. Here, we identified a previously uncharacterized mammalian-specific protein, Beclin 2, which, like Beclin 1, functions in autophagy and interacts with class III PI3K complex components and Bcl-2. However, Beclin 2, but not Beclin 1, functions in an additional lysosomal degradation pathway. Beclin 2 is required for ligand-induced endolysosomal degradation of several G protein-coupled receptors (GPCRs) through its interaction with GASP1. Beclin 2 homozygous knockout mice have decreased embryonic viability, and heterozygous knockout mice have defective autophagy, increased levels of brain cannabinoid 1 receptor, elevated food intake, and obesity and insulin resistance. Our findings identify Beclin 2 as a converging regulator of autophagy and GPCR turnover and highlight the functional and mechanistic diversity of Beclin family members in autophagy, endolysosomal trafficking, and metabolism.
[Show abstract][Hide abstract] ABSTRACT: One approach to infer functions of new proteins from their homologs utilizes visualization of an all-against-all pairwise similarity network (A2ApsN) that exploits the speed of BLAST and avoids the complexity of multiple sequence alignment. However, identifying functions of the protein clusters in A2ApsN is never trivial, due to a lack of linking characterized proteins to their relevant information in current software packages. Given the database errors introduced by automatic annotation transfer, functional deduction should be made from proteins with experimental studies, i.e. "reference proteins". Here, we present a web server, termed Pclust, which provides a user-friendly interface to visualize the A2ApsN, placing emphasis on such "reference proteins" and providing access to their full information in source databases, e.g. articles in PubMed. The identification of "reference proteins" and the ease of cross-database linkage will facilitate understanding the functions of protein clusters in the network, thus promoting interpretation of proteins of interest.
The Pclust server is freely available at http://prodata.swmed.edu/pclust CONTACT: email@example.com; firstname.lastname@example.org.
[Show abstract][Hide abstract] ABSTRACT: VEGF and PDGF receptors are implicated in development and tumorigenesis and dual inhibitors like sunitinib are prescribed for cancer treatment. While mammalian VEGF and PDGF receptors are present in multiple isoforms and heterodimers, Drosophila encodes one ancestral PDGF/VEGF receptor, PVR. We identified PVR in an unbiased cell-based RNAi screen of all Drosophila kinases and phosphatases for novel regulators of TORC1. PVR is essential to sustain TORC1 and ERK activity in cultured insect cells and for maximal stimulation by insulin. CG32406 (hereafter PVRAP, for PVR adaptor protein), an SH2-domain containing protein, binds PVR and is required for TORC1 activation. TORC1 activation by PVR involves Tsc1/Tsc2 and, in a cell type-dependent manner, Lobe|PRAS40. PVR is required for cell survival in vitro, and both PVR and TORC1 are necessary for hemocyte expansion in vivo. Constitutive PVR activation induces tumor-like structures that exhibit high TORC1 activity. Like its mammalian orthologs, PVR is inhibited by sunitinib, and sunitinib treatment phenocopies PVR loss in hemocytes. Sunitinib inhibits TORC1 in insect cells, and sunitinib-mediated TORC1 inhibition requires an intact Tsc1/Tsc2 complex. Sunitinib similarly inhibited TORC1 in human endothelial cells in a Tsc1/Tsc2-dependent manner. Our findings provide insight into the mechanism of action of PVR and may have implications for understanding sunitinib sensitivity and resistance in tumors.
Molecular and cellular biology 07/2013; · 6.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Endopeptidase classification based on catalytic mechanism and evolutionary history has proven to be invaluable to the study of proteolytic enzymes. Such general mechanistic- and evolutionary- based groupings have launched experimental investigations, because knowledge gained for one family member tends to apply to the other closely related enzymes. The serine endopeptidases represent one of the most abundant and diverse groups, with their apparently successful proteolytic mechanism having arisen independently many times throughout evolution, giving rise to the well-studied soluble chemotrypsins and subtilisins, among many others. A large and diverse family of polytopic transmembrane proteins known as rhomboids has also evolved the serine protease mechanism. While the spatial structure, mechanism, and biochemical function of this family as intramembrane proteases has been established, the cellular roles of these enzymes as well as their natural substrates remain largely undetermined. While the evolutionary history of rhomboid proteases has been debated, sorting out the relationships among current day representatives should provide a solid basis for narrowing the knowledge gap between their biochemical and cellular functions. Indeed, some functional characteristics of rhomboid proteases can be gleaned from their evolutionary relationships. Finally, a specific case where phylogenetic profile analysis has identified proteins that contain a C-terminal processing motif (GlyGly-Cterm) as co-occurring with a set of bacterial rhomboid proteases provides an example of potential target identification through bioinformatics. This article is part of a Special Issue entitled: Intramembrane Proteases.
Biochimica et Biophysica Acta 07/2013; · 4.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Renal cell carcinoma (RCC) clusters in some families. Familial RCC arises from mutations in several genes, including VHL, which is also mutated in sporadic RCC. However, a significant percentage of familial RCC remains unexplained. Recently, we discovered that the BAP1 gene is mutated in sporadic RCC. BAP1, which encodes a nuclear deubiquitinase, is a two-hit tumor suppressor gene. Somatic BAP1 mutations are associated with high-grade ccRCC and poor patient outcomes. To determine whether BAP1 predisposes to familial RCC, we sequenced the BAP1 gene in 83 unrelated probands with unexplained familial RCC. We identified a novel variant (c.41T>A; p.L14H), which cosegregated with the RCC phenotype. The p.L14H variant targets a highly conserved residue in the catalytic domain, a domain frequently targeted by missense mutations. The family with the BAP1 variant was characterized by early-onset clear cell RCC, occasionally of high Fuhrman grade, and lacked other features that characterize von Hippel-Lindau syndrome. These findings suggest that BAP1 is a familial RCC predisposing gene.
Molecular Cancer Research 05/2013; · 4.35 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The lysosomal degradation pathway of autophagy has a crucial role in defence against infection, neurodegenerative disorders, cancer and ageing. Accordingly, agents that induce autophagy may have broad therapeutic applications. One approach to developing such agents is to exploit autophagy manipulation strategies used by microbial virulence factors. Here we show that a peptide, Tat–beclin 1—derived from a region of the autophagy protein, beclin 1, which binds human immunodeficiency virus (HIV)-1 Nef—is a potent inducer of autophagy, and interacts with a newly identified negative regulator of autophagy, GAPR-1 (also called GLIPR2). Tat–beclin 1 decreases the accumulation of polyglutamine expansion protein aggregates and the replication of several pathogens (including HIV-1) in vitro, and reduces mortality in mice infected with chikungunya or West Nile virus. Thus, through the characterization of a domain of beclin 1 that interacts with HIV-1 Nef, we have developed an autophagy-inducing peptide that has potential efficacy in the treatment of human diseases. Autophagy functions in metazoans in cellular and tissue homeostasis, physiology, development, and protection against disease, and abnor-malities in autophagy may contribute to many different pathophysio-logical conditions 1,2 . Thus, strategies that augment autophagy may prevent or treat human disease 3 . Although some drugs in clinical use are capable of augmenting autophagy, these compounds exert pleiotropic effects, revealing an unmet need to develop specific indu-cers of autophagy. We sought to develop a specific autophagy-inducing agent with a potentially wide range of therapeutic effects. As viruses often provide key insights into the functionally important domains of host proteins, we investigated the molecular determinants governing the interaction between beclin 1, an essential autophagy protein in the class III phos-phatidylinositol-3-OH kinase (PI(3)K) complex involved in auto-phagic vesicle nucleation 4 , and the HIV-1 virulence factor, Nef 5 . These investigations led us to identify a Nef-interacting sequence of beclin 1 that is necessary and sufficient for autophagy induction and which provided the basis for the development of an autophagy-indu-cing peptide drug that has benefits in the clearance of polyglutamine expansion protein aggregates and the treatment of infectious diseases.
[Show abstract][Hide abstract] ABSTRACT: The lysosomal degradation pathway of autophagy has a crucial role in defence against infection, neurodegenerative disorders, cancer and ageing. Accordingly, agents that induce autophagy may have broad therapeutic applications. One approach to developing such agents is to exploit autophagy manipulation strategies used by microbial virulence factors. Here we show that a peptide, Tat-beclin 1-derived from a region of the autophagy protein, beclin 1, which binds human immunodeficiency virus (HIV)-1 Nef-is a potent inducer of autophagy, and interacts with a newly identified negative regulator of autophagy, GAPR-1 (also called GLIPR2). Tat-beclin 1 decreases the accumulation of polyglutamine expansion protein aggregates and the replication of several pathogens (including HIV-1) in vitro, and reduces mortality in mice infected with chikungunya or West Nile virus. Thus, through the characterization of a domain of beclin 1 that interacts with HIV-1 Nef, we have developed an autophagy-inducing peptide that has potential efficacy in the treatment of human diseases.
[Show abstract][Hide abstract] ABSTRACT: WNK1 is a 250 kDa serine/threonine protein kinase involved in the maintenance of cellular salt levels and is directly linked to a hereditary form of hypertension. Here, we report the solution NMR structure of the autoinhibitory domain of WNK1 (WNK1-AI), a small regulatory subunit that lies immediately C-terminal of the kinase domain. We show that this domain is a homolog of the RFXV-binding PASK/FRAY homology 2 (PF2) domain found in OSR and SPAK kinases, which are substrates ofWNK1. TheWNK1-AI has a circularly permuted topology relative to the OSR1/PF2 domain. Nevertheless, like PF2 domains, WNK1-AI binds peptides that contain an RFXV motif with micromolar affinities as assessed by changes in (1)H,(15)N HSQC spectra. Mutations to the WNK1-AI and binding peptides confirm a similar binding mode.
Journal of Molecular Biology 01/2013; · 3.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: BACKGROUND: The size of the protein sequence database has been exponentially increasing due to advances in genome sequencing. However, experimentally characterized proteins only constitute a small portion of the database, such that the majority of sequences have been annotated by computational approaches. Current automatic annotation pipelines inevitably introduce errors, making the annotations unreliable. Instead of such error-prone automatic annotations, functional interpretation should rely on annotations of 'reference proteins' that have been experimentally characterized or manually curated. RESULTS: The Seq2Ref server uses BLAST to detect proteins homologous to a query sequence and identifies the reference proteins among them. Seq2Ref then reports publications with experimental characterizations of the identified reference proteins that might be relevant to the query. Furthermore, a rating system is developed to evaluate the homologous relationships and rank the reference proteins by their relevance to the query. CONCLUSIONS: The reference proteins detected by our server will lend insight on the protein of unknown function and provide extensive information to develop in-depth understanding of the protein under study. Seq2Ref is available at: http://prodata.swmed.edu/wenlin/server/seq2ref/
[Show abstract][Hide abstract] ABSTRACT: ABSTRACT Tuberculosis, caused by Mycobacterium tuberculosis, remains a devastating human infectious disease, causing two million deaths annually. We previously demonstrated that M. tuberculosis induces an enzyme, heme oxygenase (HO1), that produces carbon monoxide (CO) gas and that M. tuberculosis adapts its transcriptome during CO exposure. We now demonstrate that M. tuberculosis carries a novel resistance gene to combat CO toxicity. We screened an M. tuberculosis transposon library for CO-susceptible mutants and found that disruption of Rv1829 (carbon monoxide resistance, Cor) leads to marked CO sensitivity. Heterologous expression of Cor in Escherichia coli rescued it from CO toxicity. Importantly, the virulence of the cor mutant is attenuated in a mouse model of tuberculosis. Thus, Cor is necessary and sufficient to protect bacteria from host-derived CO. Taken together, this represents the first report of a role for HO1-derived CO in controlling infection of an intracellular pathogen and the first identification of a CO resistance gene in a pathogenic organism. IMPORTANCE Macrophages produce a variety of antimicrobial molecules, including nitric oxide (NO), hydrogen peroxide (H2O2), and acid (H+), that serve to kill engulfed bacteria. In addition to these molecules, human and mouse macrophages also produce carbon monoxide (CO) gas by the heme oxygenase (HO1) enzyme. We observed that, in contrast to other bacteria, mycobacteria are resistant to CO, suggesting that this might be an evolutionary adaptation of mycobacteria for survival within macrophages. We screened a panel of ~2,500 M. tuberculosis mutants to determine which genes are required for survival of M. tuberculosis in the presence of CO. Within this panel, we identified one such gene, cor, that specifically confers CO resistance. Importantly, we found that the ability of M. tuberculosis cells carrying a mutated copy of this gene to cause tuberculosis in a mouse disease model is significantly attenuated. This indicates that CO resistance is essential for mycobacterial survival in vivo.
[Show abstract][Hide abstract] ABSTRACT: Structural backbones of iron-scavenging siderophore molecules include polyamines 1,3-diaminopropane and 1,5-diaminopentane (cadaverine). For the cadaverine-based desferroxiamine E siderophore in Streptomyces coelicolor, the corresponding biosynthetic gene cluster contains an ORF encoded by desA that was suspected of producing the cadaverine (decarboxylated lysine) backbone. However, desA encodes an l-2,4-diaminobutyrate decarboxylase (DABA DC) homologue and not any known form of lysine decarboxylase (LDC). The only known function of DABA DC is, together with l-2,4-aminobutyrate aminotransferase (DABA AT), to synthesize 1,3-diaminopropane. We show here that S. coelicolor desA encodes a novel LDC and we hypothesized that DABA DC homologues present in siderophore biosynthetic clusters in the absence of DABA AT ORFs would be novel LDCs. We confirmed this by correctly predicting the LDC activity of a DABA DC homologue from a Yersinia pestis siderophore biosynthetic pathway. The corollary was confirmed for a DABA DC homologue, adjacent to a DABA AT ORF in a siderophore pathway in the cyanobacterium Anabaena variabilis, which was shown to be a bona fide DABA DC. These findings enable prediction of whether a siderophore pathway will utilize 1,3-diaminopropane or cadaverine, and suggest that the majority of bacteria use DABA AT and DABA DC for siderophore, rather than norspermidine/polyamine biosynthesis.
[Show abstract][Hide abstract] ABSTRACT: RIG-I and MDA5 detect viral RNA in the cytoplasm and activate signaling cascades leading to the production of type-I interferons. RIG-I is activated through sequential binding of viral RNA and unanchored lysine-63 (K63) polyubiquitin chains, but how polyubiquitin activates RIG-I and whether MDA5 is activated through a similar mechanism remain unresolved. Here, we showed that the CARD domains of MDA5 bound to K63 polyubiquitin and that this binding was essential for MDA5 to activate the transcription factor IRF3. Mutations of conserved residues in MDA5 and RIG-I that disrupt their ubiquitin binding also abrogated their ability to activate IRF3. Polyubiquitin binding induced the formation of a large complex consisting of four RIG-I and four ubiquitin chains. This hetero-tetrameric complex was highly potent in activating the antiviral signaling cascades. These results suggest a unified mechanism of RIG-I and MDA5 activation and reveal a unique mechanism by which ubiquitin regulates cell signaling and immune response.
[Show abstract][Hide abstract] ABSTRACT: The molecular pathogenesis of renal cell carcinoma (RCC) is poorly understood. Whole-genome and exome sequencing followed by innovative tumorgraft analyses (to accurately determine mutant allele ratios) identified several putative two-hit tumor suppressor genes, including BAP1. The BAP1 protein, a nuclear deubiquitinase, is inactivated in 15% of clear cell RCCs. BAP1 cofractionates with and binds to HCF-1 in tumorgrafts. Mutations disrupting the HCF-1 binding motif impair BAP1-mediated suppression of cell proliferation but not deubiquitination of monoubiquitinated histone 2A lysine 119 (H2AK119ub1). BAP1 loss sensitizes RCC cells in vitro to genotoxic stress. Notably, mutations in BAP1 and PBRM1 anticorrelate in tumors (P = 3 × 10(-5)), and combined loss of BAP1 and PBRM1 in a few RCCs was associated with rhabdoid features (q = 0.0007). BAP1 and PBRM1 regulate seemingly different gene expression programs, and BAP1 loss was associated with high tumor grade (q = 0.0005). Our results establish the foundation for an integrated pathological and molecular genetic classification of RCC, paving the way for subtype-specific treatments exploiting genetic vulnerabilities.
[Show abstract][Hide abstract] ABSTRACT: Protein phosphorylation is a fundamental mechanism regulating nearly every aspect of cellular life. Several secreted proteins are phosphorylated, but the kinases responsible are unknown. We identified a family of atypical protein kinases that localize within the Golgi apparatus and are secreted. Fam20C appears to be the Golgi casein kinase that phosphorylates secretory pathway proteins within S-x-E motifs. Fam20C phosphorylates the caseins and several secreted proteins implicated in biomineralization, including the small integrin-binding ligand, N-linked glycoproteins (SIBLINGs). Consequently, mutations in Fam20C cause an osteosclerotic bone dysplasia in humans known as Raine syndrome. Fam20C is thus a protein kinase dedicated to the phosphorylation of extracellular proteins.