Abstract
Subunit and DNA-based vaccines against
Mycobacterium avium
ssp.
paratuberculosis
(MAP) attempt to overcome inherent issues associated with whole-cell formulations. However, these vaccines ...can be hampered by poor expression of recombinant antigens from a number of disparate hosts. The high G+C content of MAP invariably leads to a codon bias throughout gene expression. To investigate if the codon bias affects recombinant MAP antigen expression, the open reading frame of a MAP-specific antigen MptD (MAP3733c) was codon optimised for expression against a
Lactobacillus salivarius
host. Of the total 209 codons which constitute MAP3733c, 172 were modified resulting in a reduced G+C content from 61% for the native gene to 32.7% for the modified form. Both genes were placed under the transcriptional control of the PnisA promoter; allowing controlled heterologous expression in
L. salivarius
. Expression was monitored using fluorescence microscopy and microplate fluorometry via GFP tags translationally fused to the C-termini of the two
MptD
genes. A > 37-fold increase in expression was observed for the codon-optimised MAP3733synth variant over the native gene. Due to the low cost and improved expression achieved, codon optimisation significantly improves the potential of
L
.
salivarius
as an oral vaccine stratagem against Johne's disease.
The manuscript clearly demonstrates that codon optimization improves expression and hence provides a simple but effective way to increase expression levels of the target antigen in a host organism. The underlying approach of expressing
Mycobacterium avium paratuberculosis
(MAP) genes in
Lactobacillus
strains is also an interesting idea which has the potential to help immunize cattle against Johne's disease. As this was the first direct assessment of the impact of MAP codon bias on expression in a heterologous host, this study is of importance to the field.
Magnetic-plasmonic, Fe
O
-Au, core-shell nanoparticles are popular in many applications, most notably in therapeutics and diagnostics, and thus, the imaging of these nanostructures in biological ...samples is of high importance. These nanostructures are typically imaged in biological material by dark field scatter imaging, which requires an even distribution of nanostructures in the sample and, therefore, high nanoparticle doses, potentially leading to toxicology issues. Herein, we explore the nonlinear optical properties of magnetic nanoparticles coated with various thicknesses of gold using the open aperture z-scan technique to determine the nonlinear optical properties and moreover, predict the efficacy of the nanostructures in nonlinear imaging. We find that the magnetic nanoparticles coated with gold nanoseeds and thinner gold shells (ca. 4 nm) show the largest nonlinear absorption coefficient β and imaginary part of the third-order susceptibility Im χ
, suggesting that these nanostructures would be suitable contrast agents. Next, we combine laser dark field microscopy and epi-detected coherent anti-Stokes Raman (CARS) microscopy to image the uptake of magnetic-plasmonic nanoparticles in human pancreatic cancer cells. We show the epi-detected CARS technique is suitable for imaging of the magnetic-plasmonic nanoparticles without requiring a dense distribution of nanoparticles. This technique achieves superior nanoparticle contrasting over both epi-detected backscatter imaging and transmission dark field imaging, while also attaining label-free chemical contrasting of the cell. Lastly, we show the high biocompatibility of the Fe
O
nanoparticles with ca. 4-nm thick Au shell at concentrations of 10-100 µg/mL.
Enzymes serving as respiratory complex II belong to the succinate:quinone oxidoreductases superfamily that comprises succinate:quinone reductases (SQRs) and quinol:fumarate reductases. The SQR from ...the extreme thermophile
Thermus thermophilus has been isolated, identified and purified to homogeneity. It consists of four polypeptides with apparent molecular masses of 64, 27, 14 and 15
kDa, corresponding to SdhA (flavoprotein), SdhB (iron–sulfur protein), SdhC and SdhD (membrane anchor proteins), respectively. The existence of 2Fe–2S, 4Fe–4S and 3Fe–4S iron–sulfur clusters within the purified protein was confirmed by electron paramagnetic resonance spectroscopy which also revealed a previously unnoticed influence of the substrate on the signal corresponding to the 2Fe–2S cluster. The enzyme contains two heme
b cofactors of reduction midpoint potentials of −20
mV and −160
mV for
b
H and
b
L, respectively. Circular dichroism and blue-native polyacrylamide gel electrophoresis revealed that the enzyme forms a trimer with a predominantly helical fold. The optimum temperature for succinate dehydrogenase activity is 70
°C, which is in agreement with the optimum growth temperature of
T. thermophilus. Inhibition studies confirmed sensitivity of the enzyme to the classical inhibitors of the active site, as there are sodium malonate, sodium diethyl oxaloacetate and 3-nitropropionic acid. Activity measurements in the presence of the semiquinone analog, nonyl-4-hydroxyquinoline-N-oxide (NQNO) showed that the membrane part of the enzyme is functionally connected to the active site. Steady-state kinetic measurements showed that the enzyme displays standard Michaelis–Menten kinetics at a low temperature (30
°C) with a
K
M for succinate of 0.21
mM but exhibits deviation from it at a higher temperature (70
°C). This is the first example of complex II with such a kinetic behavior suggesting positive cooperativity with
k' of 0.39
mM and Hill coefficient of 2.105. While the crystal structures of several SQORs are already available, no crystal structure of type A SQOR has been elucidated to date. Here we present for the first time a detailed biophysical and biochemical study of type A SQOR—a significant step towards understanding its structure–function relationship.
►Succinate unusually influences the EPR spectrum of complex II. ►
T. thermophilus complex II exhibits positive cooperativity at high temperature. ►Trimeric complex II from
T. thermophilus belongs to type A SQORs.
In bacteria, oxidation of sulfite to sulfate, the most common strategy for sulfite detoxification, is mainly accomplished by the molybdenum-containing sulfite:acceptor oxidoreductases (SORs). ...Bacterial SORs are very diverse proteins; they can exist as monomers or homodimers of their core subunit, as well as heterodimers with an additional cytochrome c subunit. We have previously described the homodimeric SOR from Thermus thermophilus HB8 (SORTTHB8), identified its physiological electron acceptor, cytochrome c550, and demonstrated the key role of the latter in coupling sulfite oxidation to aerobic respiration. Herein, the role of this di-heme cytochrome c was further investigated. The cytochrome was shown to be composed of two conformationally independent domains, each containing one heme moiety. Each domain was separately cloned, expressed in E. coli and purified to homogeneity. Stopped-flow experiments showed that: i) the N-terminal domain is the only one accepting electrons from SORTTHB8; ii) the N- and C-terminal domains are in rapid redox equilibrium and iii) both domains are able to transfer electrons further to cytochrome c552, the physiological substrate of the ba3 and caa3 terminal oxidases. These findings show that cytochrome c550 functions as a electron shuttle, without working as an electron wire with one heme acting as the electron entry and the other as the electron exit site. Although contribution of the cytochrome c550 C-terminal domain to T. thermophilus sulfur respiration seems to be dispensable, we suggest that di-heme composition of the cytochrome physiologically enables storage of the two electrons generated from sulfite oxidation, thereof ensuring efficient contribution of sulfite detoxification to the respiratory chain-mediated energy generation.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Cell-sized polyelectrolyte capsules functionalized with a redox-driven proton pump protein were assembled for the first time. The interaction of polyelectrolyte microcapsules, fabricated by ...electrostatic layer-by-layer assembly, with cytochrome c oxidase molecules was investigated. We found that the cytochrome c oxidase retained its functionality, that the functionalized microcapsules interacting with cytochrome c oxidase were permeable and that the permeability characteristics of the microcapsule shell depend on the shell components. This work provides a significant input towards the fabrication of an integrated device made of biological components and based on specific biomolecular functions and properties.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In bacteria, oxidation of sulfite to sulfate, the most common strategy for sulfite detoxification, is mainly accomplished by the molybdenum-containing sulfite:acceptor oxidoreductases (SORs). ...Bacterial SORs are very diverse proteins; they can exist as monomers or homodimers of their core subunit, as well as heterodimers with an additional cytochrome c subunit. We have previously described the homodimeric SOR from Thermus thermophilus HB8 (SOR(TTHB8)), identified its physiological electron acceptor, cytochrome c(550), and demonstrated the key role of the latter in coupling sulfite oxidation to aerobic respiration. Herein, the role of this di-heme cytochrome c was further investigated. The cytochrome was shown to be composed of two conformationally independent domains, each containing one heme moiety. Each domain was separately cloned, expressed in E. coli and purified to homogeneity. Stopped-flow experiments showed that: i) the N-terminal domain is the only one accepting electrons from SOR(TTHB8); ii) the N- and C-terminal domains are in rapid redox equilibrium and iii) both domains are able to transfer electrons further to cytochrome c(552), the physiological substrate of the ba(3) and caa(3) terminal oxidases. These findings show that cytochrome c(550) functions as a electron shuttle, without working as an electron wire with one heme acting as the electron entry and the other as the electron exit site. Although contribution of the cytochrome c(550) C-terminal domain to T. thermophilus sulfur respiration seems to be dispensable, we suggest that di-heme composition of the cytochrome physiologically enables storage of the two electrons generated from sulfite oxidation, thereof ensuring efficient contribution of sulfite detoxification to the respiratory chain-mediated energy generation.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The understanding and the precise control of protein adsorption is extremely important for the development and optimization of biomaterials. The challenge resides in controlling the different surface ...properties, such as surface chemistry, roughness, wettability, or surface charge, independently, as modification of one property generally affects the other. We demonstrate the creation of electrically modified patterns on hydroxyapatite by using scanning electron beam to tailor the spatial regulation of protein adsorption via electrostatic interactions without affecting other surface properties of the material. We show that domains, presenting modulated surface potential, can be created to precisely promote or reduce protein adsorption.
To produce bioethanol from model cyanobacteria such as
, a two gene cassette consisting of genes encoding pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) are required to transform ...pyruvate first to acetaldehyde and then to ethanol. However the partition of pyruvate to ethanol comes at a cost, a reduction in biomass and pyruvate availability for other metabolic processes. Hence strategies to divert flux to ethanol as a biofuel in
are of interest. PDC from
(ZpPDC) has been reported to have a lower Km then the
PDC (ZmPDC), which has traditionally been used in metabolic engineering constructs. The
gene was combined with the native
alcohol dehydrogenase gene (
A) in an attempt to increase ethanol production in the photoautotrophic cyanobacterium
sp. PCC 6803 over constructs created with the traditional Zmpdc. Native (Zppdc) and codon optimized (
) versions of the ZpPDC were cloned into a construct where
expression was controlled via the
A2 light inducible promoter from
sp. PCC 6803. These constructs were transformed into wildtype
sp. PCC 6803 for expression and ethanol production. Ethanol levels were then compared with identical constructs containing the
. While strains with the
(UL071) and
(UL072) constructs did produce ethanol, levels were lower compared to a control strain (UL070) expressing the pdc from
. All constructs demonstrated lower biomass productivity illustrating that the flux from pyruvate to ethanol has a major effect on biomass and ultimately overall biofuel productivity. Thus the utilization of a PDC with a lower Km from
unusually did not result in enhanced ethanol production in
sp. PCC 6803.
Metal organic frameworks (MOFs) have been used to encapsulate an array of enzymes in a rapid and facile manner; however, the stability of MOFs as supports for enzymes has not been examined in detail. ...This study examines the stability of MOFs with different compositions (Fe-BTC, Co-TMA, Ni-TMA, Cu-TMA, and ZIF-zni) in buffered solutions commonly used in enzyme immobilization and biocatalysis. Stability was assessed via quantification of the release of metals by inductively coupled plasma optical emission spectroscopy. The buffers used had varied effects on different MOF supports, with incubation of all MOFs in buffers resulting in the release of metal ions to varying extents. Fe-BTC was completely dissolved in citrate, a buffer that has a profound destabilizing effect on all MOFs analyzed, precluding its use with MOFs. MOFs were more stable in acetate, potassium phosphate, and Tris HCl buffers. The results obtained provide a guide for the selection of an appropriate buffer with a particular MOF as a support for the immobilization of an enzyme. In addition, these results identify the requirement to develop methods of improving the stability of MOFs in aqueous solutions. The use of polymer coatings was evaluated with polyacrylic acid (PAA) providing an improved level of stability. Lipase was immobilized in Fe-BTC with PAA coating, resulting in a stable biocatalyst with retention of activity in comparison to the free enzyme.
Aldehyde dehydrogenase enzymes (ALDHs) are widely studied for their roles in disease propagation and cell metabolism. Their use in biocatalysis applications, for the conversion of aldehydes to ...carboxylic acids, has also been recognized. Understanding the structural features and functions of both prokaryotic and eukaryotic ALDHs is key to uncovering novel applications of the enzyme and probing its role in disease propagation. The thermostable enzyme ALDHTt originating fromThermus thermophilus, strain HB27, possesses a unique extension of its C-terminus, which has been evolutionarily excluded from mesophilic counterparts and other thermophilic enzymes in the same genus. In this work, the thermophilic adaptation is studied by the expression and optimized purification of mutant ALDHTt-508, with a 22-amino acid truncation of the C-terminus. The mutant shows increased activity throughout production compared to native ALDHTt, indicating an opening of the active site upon C-terminus truncation and giving rationale into the evolutionary exclusion of the C-terminal extension from similar thermophilic and mesophilic ALDH proteins. Additionally, the C-terminus is shown to play a role in controlling substrate specificity of native ALDH, particularly in excluding catalysis of certain large and certain aromatic ortho-substituted aldehydes, as well as modulating the protein’s pH tolerance by increasing surface charge. Dynamic light scattering and size-exclusion HPLC methods are used to show the role of the C-terminus in ALDHTt oligomeric stability at the cost of catalytic efficiency. Studying the aggregation rate of ALDHTt with and without a C-terminal extension leads to the conclusion that ALDHTt follows a monomolecular reaction aggregation mechanism.
PDF
