Enhanced expression of recombinant proteins in Escherichia coli by co-expression with Vibrio parahaemolyticus CsgG, a pore-forming protein of the curli biogenesis pathway

AIM

To test whether engineered nanopores on the outer membrane (OM) of Escherichia coli can increase expression of heterologous proteins by making additional nutrients available to the host.

METHODS AND RESULTS

Outer membrane nanopores were generated by expressing recombinant Vibrio parahaemolyticus CsgG (rVpCsgG), which spontaneously assembles into a pore-forming channel on the OM, allowing spontaneous diffusion of small chemical entities from the exterior. Protein expression was probed using a reporter protein, sfGFP, expressed on a second compatible plasmid. OM pore formation was shown by acquired erythromycin sensitivity in cells transformed with rVpCsgG, influx of propidium iodide as well as by surface localization of recombinant CsgG by immunogold-labeled transmission electron microscopy. Expression of recombinant CsgG showed increased growth and also enhanced expression of sfGFP in minimal medium and is due to both enhanced transcription as well as translation. Similar enhancement of expression was also observed for a number of different proteins of different origin, sizes and nature.

CONCLUSIONS

Our findings clearly demonstrate that engineered nanopores on the OM of E. coli enhance expression of different heterologous proteins in minimal medium.

SIGNIFICANCE AND IMPACT OF THE STUDY

Vibrio parahaemolyticus CsgG β-nanopore mediated co-expression strategy to improve recombinant protein expression is fully compatible with other methods of protein expression enhancement, and therefore can be a useful tool in biotechnology particularly for whole-cell bio-transformations for production of secondary metabolite.

Spontaneous shaker rat mutant - a new model for X-linked tremor/ataxia

The shaker rat is an X-linked recessive spontaneous model of progressive Purkinje cell (PC) degeneration exhibiting a shaking ataxia and wide stance. Generation of Wistar Furth (WF)/Brown Norwegian (BN) F1 hybrids and genetic mapping of F2 sib-sib offspring using polymorphic markers narrowed the candidate gene region to 26 Mbp denoted by the last recombinant genetic marker DXRat21 at 133 Mbp to qter (the end of the long arm). In the WF background, the shaker mutation has complete penetrance, results in a stereotypic phenotype and there is a narrow window for age of disease onset; by contrast, the F2 hybrid phenotype was more varied, with a later age of onset and likely non-penetrance of the mutation. By deep RNA-sequencing, five variants were found in the candidate region; four were novel without known annotation. One of the variants caused an arginine (R) to cysteine (C) change at codon 35 of the ATPase, Ca²⁺ transporting, plasma membrane 3 (Atp2b3) gene encoding PMCA3 that has high expression in the cerebellum. The variant was well supported by hundreds of overlapping reads, and was found in 100% of all affected replicas and 0% of the wild-type (WT) replicas. The mutation segregated with disease in all affected animals and the amino acid change was found in an evolutionarily conserved region of PMCA3. Despite strong genetic evidence for pathogenicity, in vitro analyses of PMCA3^R35C function did not show any differences to WT PMCA3. Because Atp2b3 mutation leads to congenital ataxia in humans, the identified Atp2b3 missense change in the shaker rat presents a good candidate for the shaker rat phenotype based on genetic criteria, but cannot yet be considered a definite pathogenic variant owing to lack of functional changes.

Summary: The shaker rat mutant: a new model for essential tremors and ataxia characterized by Purkinje cell degeneration.

Identification of a Small Molecule That Overcomes HdmX-Mediated Suppression of p53

Inactivation of the p53 tumor suppressor by mutation or overexpression of negative regulators occurs frequently in cancer. As p53 plays a key role in regulating proliferation or apoptosis in response to DNA-damaging chemotherapies, strategies aimed at reactivating p53 are increasingly being sought. Strategies to reactivate wild-type p53 include the use of small molecules capable of releasing wild-type p53 from key, cellular negative regulators, such as Hdm2 and HdmX. Derivatives of the Hdm2 antagonist Nutlin-3 are in clinical trials. However, Nutlin-3 specifically disrupts Hdm2-p53, leaving tumors harboring high levels of HdmX resistant to Nutlin-3 treatment. Here, we identify CTX1, a novel small molecule that overcomes HdmX-mediated p53 repression. CTX1 binds directly to HdmX to prevent p53-HdmX complex formation, resulting in the rapid induction of p53 in a DNA damage-independent manner. Treatment of a panel of cancer cells with CTX1 induced apoptosis or suppressed proliferation and, importantly, CTX1 demonstrates promising activity as a single agent in a mouse model of circulating primary human leukemia. CTX1 is a small molecule HdmX inhibitor that demonstrates promise as a cancer therapeutic candidate. Mol Cancer Ther; 15(4); 574-82. ©2016 AACR.

AAV-mediated gene therapy in the guanylate cyclase (RetGC1/RetGC2) double knockout mouse model of Leber congenital amaurosis

Mutations in GUCY2D are associated with recessive Leber congenital amaurosis-1 (LCA1). GUCY2D encodes photoreceptor-specific, retinal guanylate cyclase-1 (RetGC1). Reports of retinal degeneration in LCA1 are conflicting; some describe no obvious degeneration and others report loss of both rods and cones. Proof of concept studies in models representing the spectrum of phenotypes is warranted. We have previously demonstrated adeno-associated virus (AAV)-mediated RetGC1 is therapeutic in GC1ko mice, a model exhibiting loss of cones only. The purpose of this study was to characterize AAV-mediated gene therapy in the RetGC1/RetGC2 double knockout (GCdko) mouse, a model lacking rod and cone function and exhibiting progressive loss of both photoreceptor subclasses. Use of this model also allowed for the evaluation of the functional efficiency of transgenic RetGC1 isozyme. Subretinal delivery of AAV8(Y733F) vector containing the human rhodopsin kinase (hGRK1) promoter driving murine Gucy2e was performed in GCdko mice at various postnatal time points. Treatment resulted in restoration of rod and cone function at all treatment ages and preservation of retinal structure in GCdko mice treated as late as 7 weeks of age. Functional gains and structural preservation were stable for at least 1 year. Treatment also conferred cortical- and subcortical-based visually-guided behavior. Functional efficiency of transgenic RetGC1 was indistinguishable from that of endogenous isozyme in congenic wild-type (WT) mice. This study clearly demonstrates AAV-mediated RetGC1 expression restores function to and preserves structure of rod and cone photoreceptors in a degenerative model of retinal guanylate cyclase deficiency, further supporting development of an AAV-based vector for treatment of LCA1.

Vibrational spectroscopy and ionic conductivity of polyethylene oxide-NaClO4-CuO nanocomposite

Structure, morphology and thermal properties of polyethylene oxide (PEO) with sodium perchlorate (NaClO(4)) as electrolytic salt have been investigated by incorporating cupric monoxide (CuO) nanoparticles. Monoclinic CuO affects melting and glass transition temperatures of PEO-NaClO(4). Crystallinity and free ion concentration change with the variation of CuO concentration. The maximum ionic conductivity is observed for 10 wt.% CuO. Ionic conductivity follows Arrhenius type behavior as a function of temperature.

Targeting of mouse guanylate cyclase 1 (Gucy2e) to Xenopus laevis rod outer segments

Photoreceptor guanylate cyclase (GC1) is a transmembrane protein and responsible for synthesis of cGMP, the secondary messenger of phototransduction. It consists of an extracellular domain, a single transmembrane domain, and an intracellular domain. It is unknown how GC1 targets to the outer segments where it resides. To identify a putative GC1 targeting signal, we generated a series of peripheral membrane and transmembrane constructs encoding extracellular and intracellular mouse GC1 fragments fused to EGFP. The constructs were expressed in Xenopus laevis rod photoreceptors under the control of the rhodopsin promoter. We examined the localization of GFP-GC1 fusion proteins containing the complete GC1 sequence, or partial GC1 sequences, which were membrane-associated via either the GC1 transmembrane domain or the rhodopsin C-terminal palmitoyl chains. Full-length GFP-GC1 targeted to the rod outer segment disk rims. As a group, fusion proteins containing the entire cytoplasmic domain of GC1 targeted to the OS, whereas other fusion proteins containing portions of the cytoplasmic or the extracellular domains did not. We conclude that GC1 likely has no single linear peptide-based OS targeting signal. Our results suggest targeting is due to either multiple weak signals in the cytoplasmic domain of GC1, or co-transport to the OS with an accessory protein.

Enzymatic properties and regulation of the native isozymes of retinal membrane guanylyl cyclase (RetGC) from mouse photoreceptors

Mouse photoreceptor function and survival critically depend on Ca(2+)-regulated retinal membrane guanylyl cyclase (RetGC), comprised of two isozymes, RetGC1 and RetGC2. We characterized the content, catalytic constants, and regulation of native RetGC1 and RetGC2 isozymes using mice lacking guanylyl cyclase activating proteins GCAP1 and GCAP2 and deficient for either GUCY2F or GUCY2E genes, respectively. We found that the characteristics of both native RetGC isozymes were considerably different from other reported estimates made for mammalian RetGCs: the content of RetGC1 per mouse rod outer segments (ROS) was at least 3-fold lower, the molar ratio (RetGC2:RetGC1) 6-fold higher, and the catalytic constants of both GCAP-activated isozymes between 12- and 19-fold higher than previously measured in bovine ROS. The native RetGC isozymes had different basal activity and were accelerated 5-28-fold at physiological concentrations of GCAPs. RetGC2 alone was capable of contributing as much as 135-165 μM cGMP s(-1) or almost 23-28% to the maximal cGMP synthesis rate in mouse ROS. At the maximal level of activation by GCAP, this isozyme alone could provide a significantly high rate of cGMP synthesis compared to what is expected for normal recovery of a mouse rod, and this can help explain some of the unresolved paradoxes of rod physiology. GCAP-activated native RetGC1 and RetGC2 were less sensitive to inhibition by Ca(2+) in the presence of GCAP1 (EC(50Ca) ∼132-139 nM) than GCAP2 (EC(50Ca) ∼50-59 nM), thus arguing that Ca(2+) sensor properties of GCAP in a functional RetGC/GCAP complex are defined not by a particular target isozyme but the intrinsic properties of GCAPs themselves.

Ultrahigh vacuum deposition of organic molecules by electrospray ionization

An electrospray apparatus for deposition of organic molecules on surfaces in ultrahigh vacuum is presented. The kinetic energy at the impact and mass to charge ratio of deposited ions can be controlled by an electrostatic quadrupole deflector and an in-line quadrupole mass spectrometer. With an ion funnel in the first two vacuum stages a high ion transmission is achieved. Experiments on porphyrin cations and deoxyribonucleic acid deposited on a Au(111) surface demonstrate the capabilities of the instrument.

Novel functions of photoreceptor guanylate cyclases revealed by targeted deletion

Targeted deletion of membrane guanylate cyclases (GCs) has yielded new information concerning their function. Here, we summarize briefly recent results of laboratory generated non-photoreceptor GC knockouts characterized by complex phenotypes affecting the vasculature, heart, brain, kidney, and other tissues. The main emphasis of the review, however, addresses the two GCs expressed in retinal photoreceptors, termed GC-E and GC-F. Naturally occurring GC-E (GUCY2D) null alleles in human and chicken are associated with an early onset blinding disorder, termed "Leber congenital amaurosis type 1" (LCA-1), characterized by extinguished scotopic and photopic ERGs, and retina degeneration. In mouse, a GC-E null genotype produces a recessive cone dystrophy, while rods remain functional. Rod function is supported by the presence of GC-F (Gucy2f), a close relative of GC-E. Deletion of Gucy2f has very little effect on rod and cone physiology and survival. However, a GC-E/GC-F double knockout (GCdko) phenotypically resembles human LCA-1 with extinguished ERGs and rod/cone degeneration. In GCdko rods, PDE6 and GCAPs are absent in outer segments. In contrast, GC-E(-/-) cones lack proteins of the entire phototransduction cascade. These results suggest that GC-E may participate in transport of peripheral membrane proteins from the endoplasmic reticulum (ER) to the outer segments.

A model for transport of membrane-associated phototransduction polypeptides in rod and cone photoreceptor inner segments

We discuss putative mechanisms of membrane protein transport in photoreceptors based on Pde6d and Gucy2e/Gucy2f knockout mice. Knockout of the Pde6d gene encoding PrBP/delta, a prenyl binding protein present in the retina at relatively high levels, was shown to impair transport of G-protein coupled receptor kinase 1 (GRK1) and cone phosphodiesterase alpha' subunit (PDE6alpha') to the rod and cone outer segments. Other prenylated proteins are minimally affected, suggesting some specificity of interaction. Knockout of the Gucy2e gene encoding guanylate cyclase 1 (GC1) disrupted transport of G-protein coupled receptor kinase 1 (GRK1), cone PDE6alpha', cone transducin alpha and gamma subunits (cTalpha and cTgamma) to the cone outer segments, while a GC1/GC2 double knockout prevented transport of rod PDE6, but not transducin, GRK1, or rhodopsin, to the rod outer segments. These knockout phenotypes suggest that PrBP/delta functions in extracting prenylated proteins from the endoplasmic reticulum (ER) where they dock after prenylation, and that GC-bearing membranes may co-transport peripheral membrane proteins in vesicles. We conclude that distinct pathways have evolved in rods and cones for transport of integral and peripherally membrane-associated proteins.

The function of guanylate cyclase 1 and guanylate cyclase 2 in rod and cone photoreceptors

Retinal guanylate cyclases 1 and 2 (GC1 and GC2) are responsible for synthesis of cyclic GMP in rods and cones, but their individual contributions to phototransduction are unknown. We report here that the deletion of both GC1 and GC2 rendered rod and cone photoreceptors nonfunctional and unstable. In the rod outer segments of GC double knock-out mice, guanylate cyclase-activating proteins 1 and 2, and cyclic GMP phosphodiesterase were undetectable, although rhodopsin and transducin alpha-subunit were mostly unaffected. Outer segment membranes of GC1-/- and GC double knock-out cones were destabilized and devoid of cone transducin (alpha- and gamma-subunits), cone phosphodiesterase, and G protein-coupled receptor kinase 1, whereas cone pigments were present at reduced levels. Real time reverse transcription-PCR analyses demonstrated normal RNA transcript levels for the down-regulated proteins, indicating that down-regulation is posttranslational. We interpret these results to demonstrate an intrinsic requirement of GCs for stability and/or transport of a set of membrane-associated phototransduction proteins.

Congenital methemoglobinemia

A case of congenital methemoglobinemia presenting at birth is reported. The clinical signs, differential diagnosis, pathogenesis and management of this disorder are discussed.

Severe and complicated malaria in Bikaner (Rajasthan), western India

Severe and complicated malaria is an important cause of mortality in Plasmodium falciparum infection. We describe in this study the details of 532 cases of such syndromes admitted to hospital during an outbreak of malaria between September-December 1994. Increase in the annual rain fall, collection of water around Indra Gandhi Canal, forestation of shrubs around it and migration of labor, adaptation of Anopheles stephensi to desert climate and favorable breeding of An. culicifacies in the areas under impact of irrigation were presumptive causes of the outbreak in this region. Cerebral malaria (25.75%), hepatic involvement (11.47%), spontaneous bleeding (9.58%), hemoglobinuria (7.89%), severe anemia (5.83%), algid malaria (5.26%), ARDS (3%) and renal failure (2.07%) were the important manifestations. The overall mortality was 11.09%, which was high because of infection in the non-immune population of this area. Ignorance about the severity of this disease and lack of transportation facility was another important factor. Morality was highest in ARDS (81.25%) followed by severe anemia (70.97%), algid malaria (46.43%), renal failure (45.45%), jaundice (36.06%) and cerebral malaria (33.57%). Pregnancy was an important determinant increasing the mortality in female patients. Mortality was very high (82.35%) in those persons who presented with more than 3 syndromes together.

Taurine in infant nutrition

The importance of taurine in diet is poorly understood. The present evidence suggests that it is a conditionally essential aminoacid in man wherein deficiency states may result in adverse changes which will be improved with supplementation. It has a role in fat absorption in preterm infants and children with cystic fibrosis, retinal dysfunction in patients receiving TPN and those with blind loop gut syndromes. Taurine is also reported to improve maturation of ABER in pre-term infants and has a role in osmoregulation of CNS and may act as neuroinhibitor.

Purulent meningitis in the newborn

Neonatal meningitis is characterized by unusual clinical manifestations caused by unusual organisms (with a marked predominance of gram-negative organisms), a poor prognosis due to the failure of antibiotics to penetrate the blood-brain barrier, and frequent complications (ventriculitis, hydrocephalus, and brain damage). The literature is reviewed and our personal experience described. The clinical and bacteriological findings, the complications and results of various therapeutic regimes, and the factors affecting prognosis are discussed.