Characterization and Validation of Neisseria gonorrhoeae Proteins GmhAGC and NGO1985 as Molecular Targets for Development of Novel Anti-gonorrhea Therapeutic Interventions

The sexually transmitted disease gonorrhea, caused by the Gram-negative bacterium and obligate human pathogen Neisseria gonorrhoeae, remains a significant health and economic burden worldwide. In the absence of a protective vaccine, antimicrobial agents are the only pharmacological intervention for patients with gonorrhea. However, due to the remarkable ability of gonococcus to develop antibiotic resistance, infections caused by N. gonorrhoeae are believed to become untreatable in the near future. Identification and elucidation of the physiological function of novel N. gonorrhoeae proteins is critical for the formulation of new therapeutic interventions. This work focuses on characterization and validation of two gonococcal proteins, GmhA[subscript GC] and NGO1985, as targets for development of new antibiotics and a vaccine antigen, respectively. The sedoheptulose-7-phosphate isomerase, GmhA[subscript GC], is the first enzyme in the biosynthesis of nucleotide-activated-glycero-manno-heptoses. We demonstrate that N. gonorrhoeae GmhA[subscript GC] is essential for lipooligosaccharide (LOS) synthesis and pivotal for bacterial viability. Our crystallization studies have shown that GmhA[subscript GC] forms a homo-tetramer in the closed conformation with four zinc ions in the active site. Site directed mutagenesis studies showed that active site residues E65 and H183 are important for LOS synthesis but not bacterial viability, suggesting that abolition of LOS synthesis is disconnected from the GmhA[subscript GC] involvement in N. gonorrhoeae viability. NGO1985 was initially described as a hypothetical lipoprotein containing two BON (Bacterial OsmY and Nodulation) domains, hypothesized to be involved in maintaining bacterial cell envelope integrity. In our studies we demonstrate that NGO1985 is a surface exposed lipoprotein, conserved among diverse gonococcal isolates. Deletion of ngo1985 results in bacterial cell envelope defects leading to a pleiotropic phenotype including increased susceptibility to antimicrobial agents, decreased survival during in vitro growth conditions mimicking the human host environment, and high attenuation in the murine model of infection. NGO1985 interactome studies indicated a broad network of interactions including potential association with β-Barrel Assembly Machinery (Bam) complex, antibiotic efflux pump(s), and several lipoproteins. Furthermore, we demonstrate that NGO1985 does not undergo lipoprotein sorting according to the +2 residue of the lipobox motif as characterized for Escherichia coli. We determined that both BON domains, in their native orientation, are essential for NGO1985 functionality and stability. Finally, for the first time we have investigated the importance of the BON domains’ conserved glycine residues and showed that these amino acids play a critical role in protein stability. Based on the importance of both GmhA[subscript GC] and NGO1985 on gonococcal physiology, we conclude that these proteins are promising molecular targets for development of new anti-gonorrhea interventions

Functional and Structural Studies on the \u3cem\u3eNeisseria gonorrhoeae\u3c/em\u3e GmhA, the First Enzyme in the \u3cem\u3eglycero-manno\u3c/em\u3e-heptose Biosynthesis Pathways, Demonstrate a Critical Role in Lipooligosaccharide Synthesis and Gonococcal Viability

Sedoheptulose-7-phosphate isomerase, GmhA, is the first enzyme in the biosynthesis of nucleotide-activated-glycero-manno-heptoses and an attractive, yet underexploited, target for development of broad-spectrum antibiotics. We demonstrated that GmhA homologs in Neisseria gonorrhoeae and N. meningitidis (hereafter called GmhAGC and GmhANM, respectively) were interchangeable proteins essential for lipooligosaccharide (LOS) synthesis, and their depletion had adverse effects on neisserial viability. In contrast, the Escherichia coli ortholog failed to complement GmhAGC depletion. Furthermore, we showed that GmhAGC is a cytoplasmic enzyme with induced expression at mid-logarithmic phase, upon iron deprivation and anaerobiosis, and conserved in contemporary gonococcal clinical isolates including the 2016 WHO reference strains. The untagged GmhAGCcrystallized as a tetramer in the closed conformation with four zinc ions in the active site, supporting that this is most likely the catalytically active conformation of the enzyme. Finally, site-directed mutagenesis studies showed that the active site residues E65 and H183 were important for LOS synthesis but not for GmhAGC function in bacterial viability. Our studies bring insights into the importance and mechanism of action of GmhA and may ultimately facilitate targeting the enzyme with small molecule inhibitors

Group A Streptococcal S Protein Utilizes Red Blood Cells as Immune Camouflage and Is a Critical Determinant for Immune Evasion.

Group A Streptococcus (GAS) is a human-specific pathogen that evades the host immune response through the elaboration of multiple virulence factors. Although many of these factors have been studied, numerous proteins encoded by the GAS genome are of unknown function. Herein, we characterize a biomimetic red blood cell (RBC)-captured protein of unknown function-annotated subsequently as S protein-in GAS pathophysiology. S protein maintains the hydrophobic properties of GAS, and its absence reduces survival in human blood. S protein facilitates GAS coating with lysed RBCs to promote molecular mimicry, which increases virulence in vitro and in vivo. Proteomic profiling reveals that the removal of S protein from GAS alters cellular and extracellular protein landscapes and is accompanied by a decrease in the abundance of several key GAS virulence determinants. In vivo, the absence of S protein results in a striking attenuation of virulence and promotes a robust immune response and immunological memory

Structural and Functional Insights Into the Role of BamD and BamE Within the \u3cem\u3eβ\u3c/em\u3e-Barrel Assembly Machinery in \u3cem\u3eNeisseria gonorrhoeae\u3c/em\u3e

The β-barrel assembly machinery (BAM) is a conserved multicomponent protein complex responsible for the biogenesis of β-barrel outer membrane proteins (OMPs) in Gram-negative bacteria. Given its role in the production of OMPs for survival and pathogenesis, BAM represents an attractive target for the development of therapeutic interventions, including drugs and vaccines against multidrug-resistant bacteria such as Neisseria gonorrhoeae. The first structure of BamA, the central component of BAM, was from N. gonorrhoeae, the etiological agent of the sexually transmitted disease gonorrhea. To aid in pharmaceutical targeting of BAM, we expanded our studies to BamD and BamE within BAM of this clinically relevant human pathogen. We found that the presence of BamD, but not BamE, is essential for gonococcal viability. However, BamE, but not BamD, was cell-surface–displayed under native conditions; however, in the absence of BamE, BamD indeed becomes surface-exposed. Loss of BamE altered cell envelope composition, leading to slower growth and an increase in both antibiotic susceptibility and formation of membrane vesicles containing greater amounts of vaccine antigens. Both BamD and BamE are expressed in diverse gonococcal isolates, under host-relevant conditions, and throughout different phases of growth. The solved structures of Neisseria BamD and BamE share overall folds with Escherichia coli proteins but contain differences that may be important for function. Together, these studies highlight that, although BAM is conserved across Gram-negative bacteria, structural and functional differences do exist across species, which may be leveraged in the development of species-specific therapeutics in the effort to combat multidrug resistance

The Neisseria gonorrhoeae Obg protein is an essential ribosome-associated GTPase and a potential drug target

Background: Neisseria gonorrhoeae (GC) is a Gram-negative pathogen that most commonly infects mucosal surfaces, causing sexually transmitted urethritis in men and endocervicitis in women. Serious complications associated with these infections are frequent and include pelvic inflammatory disease, ectopic pregnancy, and infertility. The incidence of gonorrhea cases remains high globally while antibiotic treatment options, the sole counter measures against gonorrhea, are declining due to the remarkable ability of GC to acquire resistance. Evaluating of potential drug targets is essential to provide opportunities for developing antimicrobials with new mechanisms of action. We propose the GC Obg protein, belonging to the Obg/CgtA GTPase subfamily, as a potential target for the development of therapeutic interventions against gonorrhea, and in this study perform its initial functional and biochemical characterization. Results: We report that NGO1990 encodes Obg protein, which is an essential factor for GC viability, associates predominantly with the large 50S ribosomal subunit, and is stably expressed under conditions relevant to infection of the human host. The anti-Obg antisera cross-reacts with a panel of contemporary GC clinical isolates, demonstrating the ubiquitous nature of Obg. The cellular levels of Obg reach a maximum in the early logarithmic phase and remain constant throughout bacterial growth. The in vitro binding and hydrolysis of the fluorescent guanine nucleotide analogs mant-GTP and mant-GDP by recombinant wild type and T192AT193A mutated variants of Obg are also assessed. Conclusions: Characterization of the GC Obg at the molecular and functional levels presented herein may facilitate the future targeting of this protein with small molecule inhibitors and the evaluation of identified lead compounds for bactericidal activity against GC and other drug-resistant bacteria.Keywords: Drug target, Mant guanine nucleotides, Neisseria gonorrhoeae, GTPase, Drug resistance, Obg protein

A Metalloprotease Secreted by the Type II Secretion System Links Vibrio cholerae with Collagen

Vibrio cholerae is autochthonous to various aquatic niches and is the etiological agent of the life-threatening diarrheal disease cholera. The persistence of V. cholerae in natural habitats is a crucial factor in the epidemiology of cholera. In contrast to the well-studied V. cholerae-chitin connection, scarce information is available about the factors employed by the bacteria for the interaction with collagens. Collagens might serve as biologically relevant substrates, because they are the most abundant protein constituents of metazoan tissues and V. cholerae has been identified in association with invertebrate and vertebrate marine animals, as well as in a benthic zone of the ocean where organic matter, including collagens, accumulates. Here, we describe the characterization of the V. cholerae putative collagenase, VchC, encoded by open reading frame VC1650 and belonging to the subfamily M9A peptidases. Our studies demonstrate that VchC is an extracellular collagenase degrading native type I collagen of fish and mammalian origin. Alteration of the predicted catalytic residues coordinating zinc ions completely abolished the protein enzymatic activity but did not affect the translocation of the protease by the type II secretion pathway into the extracellular milieu. We also show that the protease undergoes a maturation process with the aid of a secreted factor(s). Finally, we propose that V. cholerae is a collagenovorous bacterium, as it is able to utilize collagen as a sole nutrient source. This study initiates new lines of investigations aiming to uncover the structural and functional components of the V. cholerae collagen utilization program.This is the publisher’s final pdf. The published article is copyrighted by the American Society for Microbiology and can be found at: http://jb.asm.org/

Polymeric Micelles as Carriers for Nerve-Highlighting Fluorescent Probe Delivery

ACS Editors' Choice - This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes.Nerve damage during surgery is a common morbidity experienced by patients that leaves them with chronic pain and/or loss of function. Currently, no clinically approved imaging technique exists to enhance nerve visualization in the operating room. Fluorescence image-guided surgery has gained in popularity and clinical acceptance over the past decade with a handful of imaging systems approved for clinical use. However, contrast agent development to complement these fluorescence-imaging systems has lagged behind with all currently approved fluorescent agents providing untargeted blood pool information. Nerve-specific fluorophores are known, however translations of these agents to the clinic has been complicated by their lipophilic nature, which necessitates specialized formulation strategies for successful systemic administration. To date the known nerve-specific fluorophores have only been demonstrated preclinically due to the necessity of a dimethyl sulfoxide containing formulation for solubilization. In the current study, a polymeric micellar (PM) formulation strategy was developed for a representative nerve-specific fluorophore from the distyrylbenzene family, BMB. The PM formulation strategy was able to solubilize BMB and demonstrated improved nerve-specific accumulation and fluorescence intensity when the same fluorophore dose was administered to mice utilizing the previous formulation strategy. The success of the PM formulation strategy will be important for moving toward clinical translation of these novel nerve-specific probes as it is nontoxic and biodegradable and has the potential to decrease the necessary dose for imaging while also improving the safety profile

Proteomics-driven Antigen Discovery for Development of Vaccines Against Gonorrhea

Expanding efforts to develop preventive gonorrhea vaccines is critical because of the dire possibility of untreatable gonococcal infections. Reverse vaccinology, which includes genome and proteome mining, has proven very successful in the discovery of vaccine candidates against many pathogenic bacteria. However, progress with this approach for a gonorrhea vaccine remains in its infancy. Accordingly, we applied a comprehensive proteomic platform—isobaric tagging for absolute quantification coupled with two-dimensional liquid chromatography and mass spectrometry—to identify potential gonococcal vaccine antigens. Our previous analyses focused on cell envelopes and naturally released membrane vesicles derived from four different Neisseria gonorrhoeae strains. Here, we extended these studies to identify cell envelope proteins of N. gonorrhoeae that are ubiquitously expressed and specifically induced by physiologically relevant environmental stimuli: oxygen availability, iron deprivation, and the presence of human serum. Together, these studies enabled the identification of numerous potential gonorrhea vaccine targets. Initial characterization of five novel vaccine candidate antigens that were ubiquitously expressed under these different growth conditions demonstrated that homologs of BamA (NGO1801), LptD (NGO1715), and TamA (NGO1956), and two uncharacterized proteins, NGO2054 and NGO2139, were surface exposed, secreted via naturally released membrane vesicles, and elicited bactericidal antibodies that cross-reacted with a panel of temporally and geographically diverse isolates. In addition, analysis of polymorphisms at the nucleotide and amino acid levels showed that these vaccine candidates are highly conserved among N. gonorrhoeae strains. Finally, depletion of BamA caused a loss of N. gonorrhoeae viability, suggesting it may be an essential target. Together, our data strongly support the use of proteomics-driven discovery of potential vaccine targets as a sound approach for identifying promising gonococcal antigens.This is the publisher’s final pdf. The published article is copyrighted by The American Society for Biochemistry and Molecular Biology and can be found at: http://www.mcponline.org/content/15/7/233

Combinatorial polymeric conjugated micelles with dual cytotoxic and antiangiogenic effects for the treatment of ovarian cancer

Emerging treatment paradigms like targeting the tumor microenvironment and/or dosing as part of a metronomic regimen are anticipated to produce better outcomes in ovarian cancer, but current drug delivery systems are lacking. We have designed and evaluated paclitaxel (PTX) and rapamycin (RAP) micellar systems that can be tailored for various dosing regimens and target tumor microenvironment. Individual and mixed PTX/RAP (MIX-M) micelles are prepared by conjugating drugs to a poly­(ethylene glycol)-<i>block</i>-poly­(β-benzyl l-aspartate) using a pH-sensitive linker. The micelles release the drug(s) at pH 5.5 indicating preferential release in the acidic endosomal/lysosomal environment. Micelles exhibit antiproliferative effects in ovarian cell cancer lines (SKOV-3 (human caucasian ovarian adenocarcinoma) and ES2 (human ovarian clear cell carcinoma)) and an endothelial cell line (HUVEC; human umbilical vein endothelial cells) with the MIX-M being synergistic. The micelles also inhibited endothelial migration and tube formation. In healthy mice, micelles at 60 mg/kg/drug demonstrated no acute toxicity over 21 days. ES2 xenograft model efficacy studies at 20 mg/kg/drug dosed every 4 days and evaluated at 21 days indicate that the individual micelles exhibit antiangiogenic effects, while the MIX-M exhibited both antiangiogenic and apoptotic induction that results in significant tumor volume reduction. On the basis of our results, MIX-M micelles can be utilized to achieve synergistic apoptotic and antiangiogenic effects when treated at frequent low doses