In vitro refolded napin-like protein of Momordica charantia expressed in Escherichia coli displays properties of native napin

Napins belong to the family of 2S albumin seed storage proteins and are shown to possess antifungal activity. Napins, in general, consist of two subunits (derived from single precursor) linked by disulphide bridges. Usually, reducing environment of the E. coli cytosol is not conducive for proper folding of heterodimeric proteins containing disulphide bridges. Present investigation reports for the first time expression of napin-like protein of Momordica charantia (rMcnapin) in E. coli and its in vitro refolding to produce biologically active protein. Full-length cDNA encoding napin-like protein (2S albumin) was isolated from M. charantia seeds by immunoscreening a cDNA expression library. The cDNA consisted of an open reading frame encoding a protein of 140 amino acid residues. The 36 amino acids at the N-terminus represent the signal and propeptide. The region encoding small and large chains of the M. charantia napin is separated by a linker of 8 amino acid residues. The region encoding napin (along with the linker) was PCR amplified, cloned into pQE-30 expression vector and expressed in E. coli. rMcnapin expressed as inclusion bodies was solubilized and purified by Ni2+-NTA affinity chromatography. The denatured and reduced rMcnapin was refolded by rapid dilution in an alkaline buffer containing glycerol and redox couple (GSH and GSSG). Refolded His-rMcnapin displayed similar spectroscopic properties as that of mature napin-like protein of M. charantia with 48.7% alpha-helical content. In addition, it also exhibited antifungal activity against T. hamatum with IC50 of 3 microg/ml. Refolded His-rMcnapin exhibited approximately 90% antifungal activity when compared with that of mature napin-like protein of M. charantia. Thus, a heterologous expression system and in vitro refolding conditions to obtain biologically active napin-like protein of M. charantia were established.     

Alteration in virulence characteristics of biofilm cells of Pseudomonas aeruginosa in presence of Tamm-Horsfall protein

Summary Tamm-Horsfall glycoprotein is the most abundant protein in human urine. The present investigation was planned to study the effect of Tamm-Horsfall protein (THP) on elaboration of virulence factors by biofilm cells of Pseudomonas aeruginosa. It was observed that with increase in concentration of THP from 10 to 50 μg/ml there was significant enhancement in elaboration of all the virulence factors by biofilm cells of P. aeruginosa. However, with further increase in concentration of THP from 50 to 70 μg/ml, significant decrease in elaboration of all the virulence traits was observed. Implications of these findings in relation to urinary tract infections caused by P. aeruginosa have been discussed.     

Role of AUX1 in the control of organ identity during in vitro organogenesis and in mediating tissue specific auxin and cytokinin interaction in <Emphasis Type="Italic">Arabidopsis</Emphasis>

Classic plant tissue culture experiments have shown that exposure of cell culture to a high auxin to cytokinin ratio promotes root formation and a low auxin to cytokinin ratio leads to shoot regeneration. It has been widely accepted that auxin and cytokinin play an antagonistic role in the control of organ identities during organogenesis in vitro. Since the auxin level is highly elevated in the shoot meristem tissues, it is unclear how a low auxin to cytokinin ratio promotes the regeneration of shoots. To identify genes mediating the cytokinin and auxin interaction during organogenesis in vitro, three allelic mutants that display root instead of shoot regeneration in response to a low auxin to cytokinin ratio are identified using a forward genetic approach in Arabidopsis. Molecular characterization shows that the mutations disrupt the AUX1 gene, which has been reported to regulate auxin influx in plants. Meanwhile, we find that cytokinin substantially stimulates auxin accumulation and redistribution in calli and some specific tissues of Arabidopsis seedlings. In the aux1 mutants, the cytokinin regulated auxin accumulation and redistribution is substantially reduced in both calli and specific tissues of young seedlings. Our results suggest that auxin elevation and other changes stimulated by cytokinin, instead of low auxin or exogenous auxin directly applied, is essential for shoot regeneration. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Molecular cloning,sequence analysis and homology modeling of galE encoding UDP-galactose 4-epimerase of Aeromonas hydrophila

A. hydrophila, a ubiquitous gram-negative bacterium present in aquatic environments, has been implicated in illness in humans, fish and amphibians. Lipopolysaccharides (LPS), a surface component of the outer membrane, are one of the main virulent factors of gram-negative bacteria. UDP-galactose 4-epimerase (GalE) catalyses the last step in the Leloir pathway of galactose metabolism and provides precursor for the biosynthesis of extracellular LPS and capsule. Due to its key role in LPS biosynthesis, it is a potential drug target. The present study describes cloning, sequence analysis and prediction of three dimensional structure of the deduced amino acid sequence of the galE of A. hydrophila AH17. The cloned galE consists of the putative promoter-operator region, and an open reading frame of 338 amino acid residues. Sequence alignment and predicted 3Dstructure revealed that the GalE of A. hydrophila consists of the signature sequences of the epimerase super family. The present study reports the molecular modeling / 3D-structure prediction of GalE of A. hydrophila. Further, the potential regions of the enzyme that can be targeted for drug design are identified.     

Alfalfa infection model: is it a potential alternative for mouse pneumonia model to study pathogenesis of Stenotrophomonas maltophilia?

The objective of this study was to develop a new, inexpensive and simple plant model to study the virulence potential of Stenotrophomonas maltophilia. The alfalfa seedlings were visually monitored for disease symptoms till 7 days post infection with 10⁵ cfu/ml of five different strains (Sm1–Sm5) of S. maltophilia. Symptoms including yellowing of leaves, stunted roots, and brown necrotic regions on seedlings were considered as disease symptoms. Sm5 and Sm2 appeared to be most virulent in alfalfa infection model, whereas Sm3 and Sm4 were moderately virulent. Strain Sm1 was found to be weakly virulent. A comparison of alfalfa infection model was carried out with mouse pneumonia model to compare the virulence of different strains of S. maltophilia in both models. Although there was variability in the level of infection caused by different strains, in both models of study, strains Sm5 and Sm2 appeared to be most virulent and were able to cause a comparatively more severe infection. We conclude that both the models can be used to study the pathogenesis of S. maltophilia and to analyze the preliminary virulence potential of this bacterium. However, clearly, to study the virulence factors, a mouse pneumonia model would be desirable.     

Amoxicillin and specific bacteriophage can be used together for eradication of biofilm of <Emphasis Type="Italic">Klebsiella pneumoniae</Emphasis> B5055

Despite the efficacy of antibiotics as well as bacteriophages in treatment of bacterial infections, their role in treatment of biofilm associated infections is still under consideration especially in case of older biofilms. Here, efficacy of bacteriophage alone or in combination with amoxicillin, for eradication of biofilm of Klebsiella pneumoniae B5055 has been assessed. Planktonic cells as well as biofilm of K. pneumoniae B5055 grown in 96-well microtiter plates were exposed to bacteriophage and amoxicillin at various Multiplicity of Infections (MoIs) as well as at three different antibiotic concentrations (512, 256 and 128 μg/ml), respectively. After exposure to 256 μg/ml (MIC) of amoxicillin, bacterial load of planktonic culture as well as 1-day-old biofilm was reduced by a log factor of 4.1 ± 0.31 (P = 0.008) and 1.24 ± 0.27 (P < 0.05), respectively but reduction in the bacterial load of mature biofilm (8-day-old) was insignificant (P = 0.23). When 8-day-old biofilm was exposed to higher antibiotic concentration (512 μg/ml) or phage alone (MoI = 0.01) a log reduction of 2.97 ± 0.11 (P = 0.182) and 3.51 ± 0.19 (P = 0.073), respectively was observed. While on exposing to a combination of both the amoxicillin and phage, a significant reduction (P < 0.01) in bacterial load of the biofilm was seen. Hence, when antibiotic was used in combination with specific bacteriophage a greater destruction of the biofilm structure suggested that the phages could be used successfully along with antibiotic therapy. An added advantage of the combination therapy would be its ability to check formation of resistant mutants that otherwise develop easily upon using phage or antibiotic alone.     

It takes two to tango to the melanosome

The role of clathrin adaptor proteins in sorting cargo in the biosynthetic and recycling routes is an area of intense research. In this issue, Delevoye et al. (2009. J. Cell Biol. doi:10.1083/jcb.200907122) show that a close interaction between the clathrin adaptor AP-1 and a kinesin motor KIF13A is essential for delivering melanogenic enzymes from recycling endosomes to nascent melanosomes and for organelle biogenesis.Melanosomes, along with platelet-dense granules and lung type II alveolar cell lamellar bodies, are lysosome-related organelles (LROs), compartments that originate from endosomes but are distinct from and usually coexist with lysosomes (Fig. 1). The most characteristic features of melanosomes are their ability to synthesize and store melanin and their presence in specialized pigmented cells such as skin melanocytes and iris and retinal pigment epithelial cells (Raposo and Marks, 2007; Wasmeier et al., 2008). In this issue, Delevoye et al. (see p. 247) report a melanogenic role for the clathrin adaptor AP-1 that involves interactions between the adaptor and the plus end kinesin motor KIF13A. An impressive set of data support a scenario in which the adaptor and the motor tightly interact, like in tango, to position donor recycling endosomes (REs) near nascent melanosomes at the cell periphery and to generate tubulovesicular intermediates that deliver newly synthesized pigmenting enzymes to melanosomes.Open in a separate windowFigure 1.Role of clathrin adaptor proteins in melanosome biogenesis. Post-Golgi trafficking routes of three melanosome cargoes (Pmel17, tyrosinase, and Tyrp1) in melanocytes are shown. Newly synthesized Pmel17 is transported to the limiting membrane and intraluminal vesicles of stage I melanosomes/early sorting endosomes via the plasma membrane. This process (depicted by a question mark) might involve clathrin and AP-2. From these EEA1-positive vacuolar endosomes, Pmel17 is sorted away from the late endosome/multivesicular body pathway into stage II melanosomes. Little is known as to how the enzymes essential for melanin synthesis, tyrosinase and Tyrp1, are sorted from the TGN to early REs, and it is likely that clathrin and its adaptors are involved in this process. Tyrosinase, which binds both AP-1 and -3, is transported to stage III melanosomes from tubular regions of REs, containing Tf/TfR and Rab11, by two distinct routes: one regulated by AP-3 and the other regulated by BLOC-1, BLOC-2, and perhaps AP-1. However, Tyrp1 binds only AP-1 and not AP-3, indicating a divergence of sorting mechanisms between tyrosinase and Tyrp1. Delevoye et al. (2009) now show that AP-1 interacts with the kinesin motor KIF13A to transport recycling endosomal domains to the melanocytic cell periphery. The close apposition of Tyrp1-containing tubules with melanosomes allows cargo transfer and biogenesis of stage III and IV melanosomes. Although Tf is found in these peripheral endosomal tubules, there appears to be a filtering mechanism that sorts it out before the tubules fuse with melanosomes. It is likely, although not yet confirmed, that BLOC-1 and -2 act in concert with AP-1 to transport Tyrp1. The tissue-specific Rabs, Rab32 and Rab38, might function in any or all of these pathways.Extensive studies have shown that melanosome biogenesis occurs in two waves that correspond to four morphologically distinct stages (Fig. 1; Marks and Seabra, 2001; Raposo and Marks, 2007). The first wave (stages I and II) is the formation of immature, pigment-free ellipsoidal melanosomes from vacuolar domains of early sorting endosomes. This process requires Pmel17, an integral membrane protein that likely reaches sorting endosomes by clathrin-dependent endocytosis from the plasma membrane. Upon proteolysis in the sorting endosomes/stage I melanosomes, Pmel17 forms intraluminal proteinaceous fibrils with characteristics of amyloid. The second wave starts with the post-Golgi transport of enzymes involved in melanin synthesis such as tyrosinase and tyrosinase-related protein 1 (Tyrp1) to nascent melanosomes. Melanin deposition occurs on Pmel17 fibrils and leads to the biogenesis of mature (stages III and IV) melanosomes. The clathrin adaptors AP-1 and -3 have partially redundant functions in sorting cargo proteins to melanosomes. Melanosomal cargo proteins have dileucine motifs that are recognized differentially by AP-1 and -3 in post-Golgi endosomes (Huizing et al., 2001; Theos et al., 2005). Nascent tyrosinase is found in distinct endosomal buds that contain either AP-3 or -1 in normal melanocytes and loss of AP-3 results only in a partial mislocalization of the enzyme. As these adaptors also mediate sorting from endosomes to other compartments, additional machinery, such as biogenesis of LRO complex 1 (BLOC-1), BLOC-2, and the tissue-specific small GTPases Rab32 and Rab38, regulate cargo delivery to melanosomes. Mutations in components of this melanosomal targeting machinery result in a variety of well-studied pigmentation defects in humans and animals such as Hermansky–Pudlak syndrome (Wei, 2006).Delevoye et al. (2009) show that knockdown of AP-1 in melanocytic MNT-1 cells decreases melanin content, demonstrating that AP-1 has a role in melanogenesis. Only late-stage (III/IV) melanosomes are decreased in number; unpigmented (stage I/II) melanosomes are unaffected, indicating that AP-1 functions selectively in the second wave of melanosome biogenesis. In AP-1–depleted cells, the melanosome cargo protein Tyrp1 is retained in vacuolar endosomes in a manner similar to that seen in BLOC-1–deficient melanocytes (Setty et al., 2007). Using immunofluorescence to monitor markers of various endosomal compartments, Delevoye et al. (2009) show that AP-1 performs its melanogenic function in early REs. Interestingly, additional data show that AP-1–containing REs have a peripheral distribution in MNT-1 cells, which is strikingly different from the perinuclear localization observed in other cells. Furthermore, siRNA-mediated knockdown of AP-1, but not of AP-3, relocates RE to a pericentriolar location.How might AP-1 influence endosome position? One possibility is by its association with the plus end–directed kinesin motor KIF13A (Fig. 1). Nakagawa et al. (2000) have previously shown that a subunit of AP-1 binds the C-terminal domain of KIF13A, mediating TGN to plasma membrane transport of the mannose 6-phosphate receptor. Indeed, Delevoye et al. (2009) show that KIF13A partially colocalizes with AP-1 in MNT-1 cells and coimmunoprecipitates with both AP-1 and Tyrp1. Furthermore, knockdown of KIF13A replicates the phenotype seen with AP-1 depletion: pericentriolar clustering of RE, accumulation of Tyrp1 in vacuolar endosomes, and reduction in mature melanosomes and melanin content. Delevoye et al. (2009) go on to show that the peripheral RE localization facilitates sorting of melanosomal proteins but decreases the efficiency of transferrin (Tf) receptor (TfR) recycling to the plasma membrane. They also show the converse; i.e., the pericentriolar localization of RE decreases the efficiency of melanosomal targeting and increases the efficiency of TfR recycling. Thus, the position of REs, determined by the interaction between a clathrin adaptor and a kinesin, is key for specific sorting functions of this organelle (like TfR recycling) and also regulates the biogenesis of another organelle (the melanosome). This is a novel and exciting finding and is an emerging theme in cell biology. It was recently reported that AP-1 interacts with another plus end–directed kinesin, KIF5, which helps transport endosomes to the cell periphery (Schmidt et al., 2009).The next question that Delevoye et al. (2009) approach is what is the nature of the carriers that transport melanosomal proteins from peripheral REs to immediately adjacent stage III/IV melanosomes? Live imaging experiments showed a dynamic network of Tf-containing RE tubules that extend and retract, making contact with melanosomes for at least 30 s. Double-tilt 3D electron tomography of thick (350–400 nm) sections of cells preserved by high pressure freezing and freeze substitution, a technique recently adapted to the study of melanosomes by Hurbain et al. (2008), revealed that some of these tubular elements are continuous with the melanosomal limiting membrane and that their lumens are often connected. Collectively, these results indicate that peripheral RE domains serve to deliver biosynthetic cargo to maturing melanosomes by the coordinated actions of AP-1 and KIF13A and that the mechanism involves tubular connections rather than vesicular transport (Fig. 1).The study by Delevoye et al. (2009) beautifully demonstrates the power of carefully chosen morphological and live imaging techniques, in combination with siRNA-mediated knockdown of molecules under study, to elucidate important details of cellular sorting processes. As always, several questions emerge from their results. Does this type of mechanism also operate in perinuclear REs, which were recently shown to cooperate with adjacent TGN in biosynthetic trafficking to the plasma membrane (Cancino et al., 2007; Gravotta et al., 2007)? Do newly synthesized melanosomal enzymes move from the TGN to REs using vesicular trafficking and clathrin adaptors or, rather, result from “maturation” of REs from the TGN? What is the role of clathrin in melanosome maturation? Are AP-1 and KIF13A essential for tubulogenesis from REs as the authors speculate? How are RE proteins (e.g., TfR) prevented from incorporating into melanosomes through the tubular connections? What is the mechanism that regulates docking and fusion of RE tubules with melanosomes? Likely, Rab32 and Rab38 participate in this process, as these proteins localize to tubulovesicular endosomal structures, and their loss causes mislocalization of tyrosinase and Tyrp1 (Wasmeier et al., 2006), but the SNAREs (if any) that participate in the mechanism are still unknown. Lastly, another intriguing aspect of this study is how adaptors sort proteins by differential recognition of dileucine motifs. Tyrp1 also has a dileucine motif that exclusively binds AP-1, but not AP-3, in melanocytic cells (Theos et al., 2005), whereas tyrosinase has dileucine motifs that bind AP-1 and -3, indicating that not all dileucine motifs are equal in the eyes of the adaptor.     

A murine pneumonia model to study pathogenesis of <Emphasis Type="Italic">Stenotrophomonas maltophilia</Emphasis>

Early attempts to develop an animal model of infection appeared to support the hypothesis that Stenotrophomonas maltophilia does not cause serious sepsis when bacteria are intravenously administered to mice. This species has also been implicated in an increasing number of infections such as, bacteremia, endocarditis, ophthalmological syndromes, skin lesions, urinary, respiratory tract and gastrointestinal infections. Despite this clinical importance, the mechanisms involved in the pathogenesis of S. maltophilia infections have not been elucidated and the virulence factors of importance in the pathogenesis of S. maltophilia associated pulmonary infection remain to be characterized. The purpose of this study was to establish an infection model using 5 clinical isolates of S. maltophilia in a mouse pneumonia model. All strains were able to establish themselves in respiratory tract with peak of infection occurring at 24 h post infection. The strains were able to cause neutrophil influx, were taken up and intracellularly killed by alveolar macrophages except Sm2 that persisted for a slightly longer time in the macrophages. All strains were resistant to lytic action of serum and survived in blood confirming their ability to cause bacteremia. The strains were cleared from spleen and liver by 7th and 4th day but caused tissue damage that was measured in terms of lipid peroxidation, lactate dehydrogenase activity and histopathological examination of lung tissue homogenate. All strains caused interstitial pneumonitis in lungs of mice.     

Improved P2 phenylglycine-based hepatitis C virus NS3 protease inhibitors with alkenylic prime-side substituents

Phenylglycine has proved to be a useful P2 residue in HCV NS3 protease inhibitors. A novel π–π-interaction between the phenylglycine and the catalytic H57 residue of the protease is postulated. We hypothesized that the introduction of a vinyl on the phenylglycine might strengthen this π–π-interaction. Thus, herein is presented the synthesis and inhibitory potency of a series of acyclic vinylated phenylglycine-based HCV NS3 protease inhibitors. Surprisingly, inhibitors based on both d- and l-phenylglycine were found to be effective inhibitors, with a slight preference for the d-epimers. Furthermore, prime-side alkenylic extension of the C-terminal acylsulfonamide group gave significantly improved inhibitors with potencies in the nanomolar range (～35 nM), potencies which were retained on mutant variants of the protease.