Autodisplay: one-component system for efficient surface display and release of soluble recombinant proteins from Escherichia coli

The immunoglobulin A protease family of secreted proteins are derived from self-translocating polyprotein precursors which contain C-terminal domains promoting the translocation of the N-terminally attached passenger domains across gram-negative bacterial outer membranes. Computer predictions identified the C-terminal domain of the Escherichia coli adhesin involved in diffuse adherence (AIDA-I) as a member of the autotransporter family. A model of the beta-barrel structure, proposed to be responsible for outer membrane translocation, served as a basis for the construction of fusion proteins containing heterologous passengers. Autotransporter-mediated surface display (autodisplay) was investigated for the cholera toxin B subunit and the peptide antigen tag PEYFK. Up to 5% of total cellular protein was detectable in the outer membrane as passenger autotransporter fusion protein synthesized under control of the constitutive P(TK) promoter. Efficient presentation of the passenger domains was demonstrated in the outer membrane protease T-deficient (ompT) strain E. coli UT5600 and the ompT dsbA double mutant JK321. Surface exposure was ascertained by enzyme-linked immunosorbent assay, immunofluorescence microscopy, and immunogold electron microscopy using antisera specific for the passenger domains. In strain UT2300 (ompT+), the passenger domains were released from the cell surface by the OmpT protease at a novel specific cleavage site, R / V. Autodisplay represents a useful tool for future protein translocation studies with interesting biotechnological possibilities.

Characterization of the essential transport function of the AIDA-I autotransporter and evidence supporting structural predictions

The current model for autodisplay suggests a mechanism that allows a passenger protein to be translocated across the outer membrane by coordinate action of a C-terminal beta-barrel and its preceding linking region. The passenger protein, linker, and beta-barrel are together termed the autotransporter, while the linker and beta-barrel are here referred to as the translocation unit (TU). We characterized the minimal TU necessary for autodisplay with the adhesin-involved-in-diffuse-adherence (AIDA-I) autotransporter. The assumed beta-barrel structure at the C terminus of the AIDA-I autotransporter was studied by constructing a set of seven AIDA-I-cholera toxin B subunit fusion proteins containing various portions of AIDA-I. Surface exposure of the cholera toxin B moiety was assessed by dot blot experiments and trypsin accessibility of the chimeric proteins expressed in Escherichia coli JK321 or UT5600. Export of cholera toxin B strictly depended on a complete predicted beta-barrel region. The absolute necessity for export of a linking region and its influence on expression as an integral part of the TU was also demonstrated. The different electrophoretic mobilities of native and denatured chimeras indicated that the proposed beta-barrel resides within the C-terminal 312 amino acids of AIDA-I. Together these data provide evidence for the predicted beta-barrel structure and support our formerly proposed model of membrane topology of the AIDA-I autotransporter.

Differential roles of C4 and betaC1 in mediating suppression of post-transcriptional gene silencing: evidence for transactivation by the C2 of Bhendi yellow vein mosaic virus, a monopartite begomovirus

Bhendi yellow vein mosaic disease (BYVMD) is caused by the association of a DNA beta satellite with a begomovirus component. The begomovirus component has two promoters, one in the virion sense (V-sense) and the other in the complementary sense (C-sense) in the intergenic region (IR). To study the promoter activities of V-sense and C-sense promoters, mGFP gene fusion was made downstream to the promoters. Transient and stable expressions in N. benthamiana leaves showed significant GFP expression under C-sense promoter whereas the expression under the V-sense promoter was very weak in the absence of the transactivator C2. Untransformed N. benthamiana plants were agroinfiltrated with binary vector constructs containing V-sense-GFP alone or along with C1, C2, C4, V1, V2 or betaC1 (in both sense and antisense orientations) to understand the roles of these gene products in transactivation and/or suppression of post-transcriptional gene silencing (PTGS). The results showed strong suppression of gene silencing activities for C4 and betaC1 but a weak activity for C2. The suppression activities were also confirmed using gfp-silenced GFP16c/GFPi plants by agroinfiltration and agroinoculation. The expression of C4 and betaC1 as transgenes produced abnormal phenotypic growth compared to the other viral genes mentioned above, further supporting their suppressor function.

Absence of periplasmic DsbA oxidoreductase facilitates export of cysteine-containing passenger proteins to the Escherichia coli cell surface via the Iga beta autotransporter pathway

The Iga beta autotransporter function of IgA1 protease from Neisseria gonorrhoeae was assessed in Escherichia coli using the Vibrio cholerae toxin B subunit (CtxB) as a heterologous passenger. N-terminal fusions with Iga beta of native CtxB or mutant CtxB protein containing no cysteines were constructed and analysed in isogenic E. coli mutants carrying defects in either or both the ompT (outer membrane protease T) and dsbA (periplasmic disulfide oxidoreductase) determinants. While export of the cystein-less CtxB passenger was independent of the dsbA genotype, the native CtxB passenger was properly translocated across the outer membrane only in the dsbA mutant background. This effect was consistent in the presence and in the absence of the OmpT protease which rather determined the release of surface-bound CtxB into the medium. Therefore, in agreement with previous observations Iga beta-dependent protein secretion requires an unfolded conformation of the passenger domain and can be blocked by disulfide loop formation in the presence of DsbA. Since DsbA acts in the periplasm, this provides evidence for a periplasmic intermediate in the Iga beta-mediated export pathway. E. coli (dsbA ompT) is highly suitable as a strain for the surface display of recombinant proteins via Iga beta, whether or not they contain cysteine residues.

The Neisseria gonorrhoeae gene aniA encodes an inducible nitrite reductase

The aniA gene of Neisseria gonorrhoeae encodes an outer membrane lipoprotein which is strongly induced when gonococci are grown anaerobically in vitro in the presence of nitrite. Database searches with the amino acid sequence derived from the aniA structural gene revealed significant homologies to copper-containing nitrite reductases from several denitrifying bacteria. We constructed an insertional mutation in the aniA locus of strain MS11 by allelic replacement, to determine whether this locus was necessary for growth in oxygen-depleted environments, and to demonstrate that AniA was indeed a nitrite reductase. The mutant was severely impaired in its ability to grow micro-aerophilically in the presence of nitrite, and we observed a loss in viability over several hours of incubation. No measurable nitrite reductase activity was detected in the aniA mutant strain, and activity in the strain with a wild-type locus was inducible. Finally, we report investigations to determine whether AniA protein is involved in gonococcal pathogenesis.

Development of a simple and rapid assay for the evaluation of inhibitors of human 17alpha-hydroxylase-C(17,20)-lyase (P450cl7) by coexpression of P450cl7 with NADPH-cytochrome-P450-reductase in Escherichia coli

P450c17 is a microsomal enzyme catalyzing the last step in androgen biosynthesis. As inhibitors of P450c17 are promising drug candidates for the treatment of prostate cancer, it was our goal to develop a new cellular assay for the in vitro evaluation of potential inhibitors. Human P450c17 was expressed in E. coli and hydroxylase activity was determined using 1,2[3H]-progesterone. As the activity was low (1.7 pmol/min/mg protein), due to a lack of the requisite electron transfer partner NADPH-cytochrome-P450-reductase (NADPH-P450-reductase), coexpression of both the enzymes had to be performed. For that purpose, a plasmid was constructed which encoded human P450c17 and rat NADPH-P450-reductase in a transcriptional unit. This strategy led to a 100-fold increase in P450cl7 activity (175 pmol/min/mg protein). Time, pH and temperature dependence of progesterone conversion of this new monooxygenase system was determined. The K(M) of progesterone was 2.75 microM. An assay procedure for the evaluation of inhibitors was established and modified for high throughput screening using 96-well plates. Selected compounds were tested for their inhibitory activity using this whole cell assay. The data was compared to the results obtained in microsomal testicular preparations.

Synthesis and evaluation of novel steroidal oxime inhibitors of P450 17 (17 alpha-hydroxylase/C17-20-lyase) and 5 alpha-reductase types 1 and 2

17 alpha-Hydroxylase/C17-20-lyase (P450 17, CYP 17) and 5 alpha-reductase are the key enzymes in androgen biosynthesis and targets for the treatment of prostate cancer and benign prostatic hyperplasia. In the search of inhibitors for both enzymes, 23 pregnenolone- or progesterone-based steroids were synthesized bearing an oxime group connected directly or via a spacer to the steroidal D-ring. Tested for inhibition of human and rat P450 17, some pregnenolone (9, 11, 14) and a series of progesterone compounds (17-20) turned out to be highly active inhibitors of the human enzyme. The most active compound was Z-21-hydroxyiminopregna-5, 17(20)-dien-3 beta-ol (9) showing K(i) values of 44 and 3.4 nM for the human and rat enzymes, respectively, and a type II UV-difference spectrum indicating a coordinate bond between the oxime group and the heme iron. In contrast to the pregnenolones which showed no inhibition of 5 alpha-reductase isozymes 1 and 2, the progesterones 16, 17, 20, 21, and 23 showed marked inhibition, especially toward the type 2 enzyme. Compounds 17 and 20 were identified as potent dual inhibitors of both P450 17 and 5 alpha-reductase. Tested for selectivity, the most potent P450 17 inhibitors 9, 10, and 14 showed no or only marginal inhibition of P450 arom, P450 scc, and P450 TxA(2). Selected compounds were tested for inhibition of the target enzymes using whole-cell assays. Compounds 9-11 strongly inhibited P450 17 being coexpressed with NADPH-P450 reductase in E. coli cells, and 16, 20, and 23 markedly inhibited 5 alpha-reductase expressed in HEK 293 cells. Tested for in vivo activity, 9 (0.019 mmol/kg) decreased the plasma testosterone concentration in rats after 2 and 6 h by 57% and 44%.

Functional display of active bovine adrenodoxin on the surface of E. coli by chemical incorporation of the [2Fe-2S] cluster

The display of heterologous proteins on the surface of living cells bears promising options for a wide variety of biotechnological applications. Up to now, however, cellular surface display was merely restricted to simple polypeptide chains. Here we present for the first time the efficient display of a protein (bovine adrenodoxin) that contains an inorganic, prosthetic group in its active form on the surface of Escherichia coli. For this purpose apo-adrenodoxin was transported to the cell surface and anchored within the outer membrane by the autotransporter pathway. Incorporation of the iron-sulfur cluster was achieved by a single-vial, one-step titration under anaerobic conditions. The biological function of surface-displayed holo-adrenodoxin could be established through adrenodoxin-dependent steroid conversion by two different cytochrome P450 enzymes and the number of functional molecules on the cell surface could be determined to be more than 10(5) per cell. Neither the expression of adrenodoxin nor the incorporation of the chemical iron-sulfur cluster reduced the viability of the bacterial cells.

Methods to calibrate and scale axial distances in confocal microscopy as a function of refractive index

Accurate distance measurement in 3D confocal microscopy is important for quantitative analysis, volume visualization and image restoration. However, axial distances can be distorted by both the point spread function (PSF) and by a refractive-index mismatch between the sample and immersion liquid, which are difficult to separate. Additionally, accurate calibration of the axial distances in confocal microscopy remains cumbersome, although several high-end methods exist. In this paper we present two methods to calibrate axial distances in 3D confocal microscopy that are both accurate and easily implemented. With these methods, we measured axial scaling factors as a function of refractive-index mismatch for high-aperture confocal microscopy imaging. We found that our scaling factors are almost completely linearly dependent on refractive index and that they were in good agreement with theoretical predictions that take the full vectorial properties of light into account. There was however a strong deviation with the theoretical predictions using (high-angle) geometrical optics, which predict much lower scaling factors. As an illustration, we measured the PSF of a correctly calibrated point-scanning confocal microscope and showed that a nearly index-matched, micron-sized spherical object is still significantly elongated due to this PSF, which signifies that care has to be taken when determining axial calibration or axial scaling using such particles.

Heavy metal pollution exerts reduction/adaptation in the diversity and enzyme expression profile of heterotrophic bacteria in Cochin estuary, India

Over the past three decades heavy metal pollution has increased substantially in Cochin estuary, south west coast of India. Here we studied the distribution, diversity and enzyme expression profile of culturable microbial population along a pollution gradient. The distribution of resistance against 5 mM concentration of Zn, Co, Ni and Cu was observed among 90-100% of bacterial isolates retrieved from highly polluted Eloor, whereas it was less than 40% in Vypin and Munambam. Similarly, there was a difference in the distribution and diversity of bacterial phyla with predominance of Proteobacteria in Eloor and Firmicutes in Munambam and Vypin. We observed that 75-100% of the organisms retrieved from Eloor had low levels of expression for hydrolytic enzyme. In conclusion, the heavy metal pollution in Cochin estuary brought in reduction/adaptation in the distribution, diversity and enzyme expression profile of bacteria, which may impart adverse impacts on ecosystem functioning.

First experiences of photoacoustic imaging for detection of melanoma metastases in resected human lymph nodes

BACKGROUND AND OBJECTIVE

Excision and histological assessment of the first draining node (sentinel lymph node) is a frequently used method to assess metastatic lymph node involvement related to cutaneous melanoma. Due to the time required for accurate histological assessment, nodal status is not immediately available to the surgeon. Hence, in case histological examination shows metastases, the patient has to be recalled to perform additional lymphadenectomy. To overcome these drawbacks we studied the applicability of photoacoustic tomographic imaging as an intra-operative modality for examining the status of resected lymph nodes.

MATERIALS AND METHODS

In melanoma patients undergoing lymphadectomy for metastatic disease, six suspect lymph nodes were photoacoustically (PA) imaged using multiple wavelengths. Histopathologal examination showed three nodes without tumor cells (benign nodes) and three nodes with melanoma cells (malignant nodes). PA images were compared with histology and anatomical features were analyzed. In addition, PA spectral analysis was performed on areas of increased signal intensity.

RESULTS

After correlation with histopathology, multiple areas containing melanoma cells could be identified in the PA images due to their increased response. Malignant nodes showed a higher PA response and responded differently to an increase in excitation wavelength than benign nodes. In addition, differences in anatomical features between the two groups were detected.

CONCLUSIONS

Photoacoustic detection of melanoma metastases based on their melanin content proves to be possible in resected human lymph nodes. The amount of PA signal and several specific anatomical features seem to provide additional characteristics for nodal analysis. However, it is as yet preliminary to designate a highly accurate parameter to distinguish between malignant and benign nodes. We expect to improve the specificity of the technique with a future implementation of an adjusted illumination scheme and depth correction for photon fluence.

Constitutional genomic instability, chromosome aberrations in tumor cells and retinoblastoma

Although retinoblastoma (Rb) is initiated as a result of biallelic inactivation of the RB1 gene, additional genetic events (M3) in tumor cells are indicative of their role in the full transformation of retinal cells. We investigated the constitutional genetic instability by fragile site (FS) expression studies and checked its relationship with loci of tumor cytogenetics in a series of 36 retinoblastoma patients (34 nonfamilial and 2 familial cases). Tumor cytogenetics revealed -13/+13, del/t(13)(q14) (50%), +1/del/t(1p/q) (65%), +6/i(6p) (60%), and del(16)(q13)/(q22 approximately q23) (60%). Conventional cytogenetics in leukocytes revealed constitutional del(13q14) in five unilateral Rb (URB) and one trilateral Rb (TRB). Constitutional del(16)(q22) and t(6;12) were also identified in two cases. Constitutional FS analysis showed a significant increase in the cellular fragility, with high prevalence at 13q14, 3p14, 6p23, 16q22 approximately q23, and 13q22 loci in retinoblastoma patients (P<0.05). Patients with constitutional del(13)(q14) demonstrated higher fragility than those with normal constitution. A strong correlation between loci of constitutional FSs and loci of recurrent chromosomal abnormalities in tumors strengthen and support the proposal that FS loci present as inherent genomic instability in retinoblastoma. The chromosomal changes and resultant genetic mutations, along with RB1 mutation events, probably contribute synergistically to the development and progression of Rb malignancy. Implementation of fluorescence in situ hybridization to nonfamilial Rb on a large scale (113 cases) could detect constitutional RB1 deletion in 12.3% of cases, with equally higher incidence in URB (14.7%) and bilateral Rb (13.6%), demonstrating that the true prevalence of patients with predisposition to RB1 mutation in sporadic URB is definitely higher in our populations. Also, higher incidence of constitutional RB1 deletion mosaicism in unilateral than in bilateral Rb indicates that the constitutional genetic mosaicism in URB should be given serious consideration during genetic counseling.

Structure and dynamics of gold nanoparticles decorated with chitosan–gentamicin conjugates: ReaxFF molecular dynamics simulations to disclose drug delivery

Functionalized gold nanoparticles for antibiotic drug delivery: from the nanoscale to the atomic scale.

Esterase EstE from Xanthomonas vesicatoria ( Xv_EstE) is an outer membrane protein capable of hydrolyzing long-chain polar esters

A new esterase gene from Xanthomonas vesicatoria (formerly X. campestris) DSM 50861 was identified, cloned from a chromosomal gene library and overexpressed in Escherichia coli. The corresponding DNA fragment contains an ORF of 1,818 bp, encoding a hydrolase of the GDSL esterase family. A protein of about 67 kDa, named Xv_EstE, was expressed from this fragment. A N-terminal signal peptide was processed under low-expression conditions, yielding a 63-kDa mature protein. The predicted amino acid sequence showed distinct homology to esterases of the GDSL family. Based on homology, a catalytic triad Gly-Asp-Ser could be defined. Amino acid sequence alignments and computer-assisted structure prediction indicated the presence of a carboxyl-terminal beta-barrel membrane domain which might facilitate binding of Xv_EstE to the outer membrane. This could be verified by differential cell fractionation experiments, in which Xv_EstE was exclusively found in the outer membrane fraction. Xv_EstE showed preferential hydrolytic activity on short chain (up to C(8)) and para-substituted nitrophenylesters as substrates. However, only long-chain 1-hydroxy-pyrene-3,6,8-trisulfonic acid (HPTS)-fatty acid esters were hydrolyzed. Xv_EstE was also found to be active on a series of substrates of industrial interest, such as 1-methylprop-2-ynyl acetate, for which an enantioselectivity up to 93% ee could be recognized.

Fabrication and functionalization of 3D-printed soft and hard scaffolds with growth factors for enhanced bioactivity

Strategies to improve the acceptance of scaffolds by the body is crucial in tissue engineering (TE) which requires tailoring of the pore structure, mechanical properties and surface characteristics of the scaffolds. In the current study we used a 3-dimensional (3D) printing technique to tailor the pore structure and mechanical properties of (i) nanocellulose based hydrogel scaffolds for soft tissue engineering and (ii) poly lactic acid (PLA) based scaffolds for hard tissue engineering in combination with surface treatment by protein conjugation for tuning the scaffold bioactivity. Dopamine coating of the scaffolds enhanced the hydrophilicity and their capability to bind bioactive molecules such as fibroblast growth factor (FGF-18) for soft TE scaffolds and arginyl glycyl aspartic acid (RGD) peptide for hard TE scaffolds, which was confirmed using MALDI-TOFs. This functionalization approach enhanced the performance of the scaffolds and provided antimicrobial activity indicating that these scaffolds can be used for cartilage or bone regeneration applications. Blood compatibility studies revealed that both the materials were compatible with human red blood cells. Significant enhancement of cell attachment and proliferation confirmed the bioactivity of growth factor functionalized 3D printed soft and hard tissues. This approach of combining 3D printing with biological tuning of the interface is expected to significantly advance the development of biomedical materials related to soft and hard tissue engineering.

3D printed scaffolds with tailored bioactivity using protein conjugation.