Device

Part:BBa_K1465102

Designed by: iGEM-Team Bielefeld 2014   Group: iGEM14_Bielefeld-CeBiTec   (2014-10-03)
Revision as of 01:58, 18 October 2014 by J droste (Talk | contribs)

Fumarate reductase (frd) from E. coli under the control of the T7 promoter

Fumerate reductase (frd) from E. coli under the control of the T7 promoter

Usage and Biology

Fumarate reductase is part of the anaerobic fumarate respiration in E. coli. It catalyzes the reaction from fumarate into succinate using fumarate as a final electron acceptor in anaerobic fumarate respiration. The related enzyme in aerobic respiration is the succinate dehydrogenase, which catalyses the reaction from succinate to fumarate. The electrons are transferred from succinate to FAD+ producing fumarate and FADH2. The succinate dehydrogenase is also a membrane enzyme and it is part of the citric acid cycle. They both belong to the respiration complex II. Naturally there is no activity of both enzymes at the same time in E. coli cells. (Iverson et al., 1999)
In our project we used the fumarate reductase in combination with an extracellular mediator as electron donor to transfer electrons into bacterial cells. The reduced mediator crosses the outer membrane of E. coli through the outer membrane porine OprF (BBa_K1172507). Mediators adsorb at the inner membrane and transfer electrons to the fumarate reductase. After that the reduced fumarate reductase transfer electrons to fumarate producing succinate. This process has been shown for the fumarate reductase in Actinobacillus succinogenes by Park et al..
Succinate can serve as a substrate for the succinate dehydrogenase, which catalyzes the oxidation of succinate into fumarate again. So we want to create a loop in the citric acid cycle between fumarate and succinate generating FADH2 as a reductive power in the cell. Electrons are transferred to FAD+, which generate proton translocation from the cytoplasm into the periplasmatic space. The proton motoric force leads to ATP production. To conclude the mediator-dependent activity of the fumarate reductase could serve as an energy source for bacterial cells.
We compared the activity of the fumarate reductases (Frd) from Escherichia coli KRX working with different mediators, for example neutral red or bromphenol blue, as electron donors in our electrobiochemical H-cell reactor.


Sequence and Features


Assembly Compatibility:
  • 10
    COMPATIBLE WITH RFC[10]
  • 12
    COMPATIBLE WITH RFC[12]
  • 21
    INCOMPATIBLE WITH RFC[21]
    Illegal BglII site found at 1352
  • 23
    COMPATIBLE WITH RFC[23]
  • 25
    INCOMPATIBLE WITH RFC[25]
    Illegal AgeI site found at 666
    Illegal AgeI site found at 741
    Illegal AgeI site found at 3023
  • 1000
    COMPATIBLE WITH RFC[1000]

Results

Upon the expression of the fumarate reductase Frd in E. coli we analyzed the metabolic behavior under aerobic and anaerobic conditions. Successful expression of the fumarate reductase Frd (BBa_1465102) could be proven via SDS-PAGE. Activity of the fumarate reductase displayed with HPLC analysis of fumarate consumption and succinate production in anaerobic cultivation of E. coli was shown with BBa_1465102. Furthermore we investigated the fumarate reductase activity in different E. coli strains by phenotypic MicroArray (PM) analysis with a Biolog® system.

SDS-PAGE

The fumarate reductase could be detected in purified membrane and periplasmatic protein fractions. Proteins were fractioned by cold osmotic shock of E. coli KRX at different steps after induction of protein expression.
SDS-PAGE shows the expression of fumarate reductase in E. coli KRX under control of the T7 promotor (BBa_1465102). Fumarate reductase with a total molecular mass of 121 kD consists of four subunits. There are two large catalytic and water-soluble subunits, flavoprotein (66 kDa) and iron-sulfur protein (27 kDa). Two small membrane associated subunits (15 and 13 kDa) are not detectable in SDS-PAGE. (Iverson et al., 1999).
Figure 1 shows the result of the SDS-PAGE of isolated membrane proteins via cold osmotic shock of E. coli KRX with BBa_1465102. Membrane protein fractions at different times after induction of BBa_1465102 are displayed.


Figure 1: Results of the SDS-PAGE of purified membrane protein from Escherichia coli BBa_1465102 via cold osmotic shock. Expected size of fumarate reductase subunits A and B are 66 kDa and 27 kDA respectively. Increasing band at 66 kDa could be recognized attributable to subunit A. Increasing band between 40 and 55 kDa could be referable to dimer or trimer build-up by subunit B, C and D.

SDS-PAGE shows a significantly higher protein concentration in membrane extracts from E. coli overexpressing frd under control of T7 promoter (BBa_1465102) after induction. This is caused by usually higher membrane protein concentration of cultivated cells attributable to higher optical density. Nevertheless, a strong overexpression band can be observed at the expected Frd size (subunit A) of about 66 kDa for BBa_1465102, which can be traced back on the strong expression and overproduction of Frd. Besides an overexpression band can be recognized at a size of about 45 kDA. This could be explained by dimer formation of two or three Frd subunits, for example subunit B (27 kDa) with subunit C oder D (13 and 15 kDA). That implies that subunit B build up stable dimers with small membrane associated subunits C and D of about 40 kDa respectively 42 kDa. There seems to be no dimers of subunit A with other parts of the Frd.
Anaerobic cultivation

We cultivated E. coli KRX with BBa_1465102 under anaerobic conditions to characterize the activity of the fumarate reductase Frd (BBa_1465102) under control of the T7 promotor. We used M9 minimal medium with 50 mM xylose as carbon source and 50 mM fumarate as substrate of the fumarate reductase Frd. We focused on growth characteristic and metabolite analysis. Under anaerobic conditions E. coli cells use different alternative electron acceptors instead of oxygen. In part the bacteria use fumarate respiration, whereby fumarate is reduced into succinate. There are also other potential pathways for bacteria to release their electrons, for example anorganic compounds like nitrate (NO3-) or sulfate (SO42-). As a result of this the expected level of produced succinate is very low. We analyzed fumarate and succinate concentrations in the culture supernatant via HPLC analysis.

We expect mid-level succinate production of the E. coli KRX wildtype under anaerobic conditions. Strong expression of Frd (BBa_1465102) leads to an increasing succinate production and fumarate consumption.
As a control we are going to use E. coli ΔfdrA730::kan, an E. coli strain with a reviewed knockout in frdA gene. This strain does not show any fumarate reductase activity and so succinate concentraion should be on a low level. Furthermore we transform BBa_1465102 into E. coli ΔfdrA730::kan to compensate functional defect of fumarate reductase in this strain.
Unfortunately the results of the cultivartion of E. coli ΔfdrA730::kan and E. coli ΔfdrA730::kan with complementation by BBa_1465102 are not successful. HPLC analysis could not evaluated because of a mistake in the process.


Figure XXX: Results of the anaerobic cultivation of Escherichia coli KRX wildtype in M9 minimal medium with 50 mM xylose and 50 mM fumarate. Induction occurred after 72 h with 0.1% rhamnose and 500 μM IPTG. Fumarate and succinate concentration were measured duplicated via HPLC.


Figure XXX: Results of anaerobic cultivation of Escherichia coli KRX wildtype with strong expression of frd (BBa_1465102) in M9 minimal medium with 50 mM xylose and 50 mM fumarate. Induction occurred after 72 h with 0.1% rhamnose and 500 μM IPTG. Fumarate and succinate concentration were measured duplicated via HPLC.


Figure XXX: Growth of the Escherichia coli KRX wildtype with strong expression of frd (BBa_1465102) compared to Escherichia coli KRX wildtype under anaerobic condition in M9 minimal medium with 50 mM xylose and 50 mM fumarate. Induction occurred after 72 h with 0.1% rhamnose and 500 μM IPTG. Fumarate and succinate concentration were measured duplicated via HPLC.


Figure XXX: Comparison of fumarate consumption and succinate production in anaerobic cultivation of the Escherichia coli KRX wildtype and i>Escherichia coli KRX wildtype with strong expression of frd (BBa_1465102) in M9 minimal medium with 50 mM xylose and 50 mM fumarate. Induction occurred after 72 h with 0.1% rhamnose and 500 μM IPTG. Fumarate and succinate concentration were measured duplicated via HPLC.
As expected figure XXX shows the production of succinate by the Escherichia coli KRX wildtype under anaerobic condition with 50 mM xylose and 50 mM fumarate as sole carbon sources. Under anaerobic conditions fumarate respiration takes place. Growth displayed via OD600 shows rise in the first three days of anaerobic cultivation. After that cells were induced via 0.1% rhamnose and 500 μM IPTG. This leads to a reduction in growth because of the expression load and the toxic effect of IPTG. Cultivation of the E. coli wildtype also should be induced because of better comparability. The same effect could be observed in cultivation of E. coli with BBa_1465102, as shown in figure XXX. There is also a drop in growth detectable. Comparison of both growth characteristics are shown in figure XXX. It could be proven that there are no distinct differences in growth betweenE. coli KRX wildtype and E. coli KRX with BBa_1465102. So statement about fumarate reductase activity in E. coli KRX with BBa_1465102 as measured by succinate production and fumarate consumption is possible.
Figure XXX shows comparison of succinate production and fumarate consumption between E. coli KRX wildtype and E. coli KRX with BBa_1465102. This illustrates an increasing succinate production by E. coli KRX with BBa_1465102 after induction of T7 promotor. A higher value of succinate could be achieved after 8 days of anaerobic cultivation and also lower fumarate level was shown compared to E. coli KRX wildtype.

References

  • Iverson et al., 1999. Structure of the Escherichia coli Fumarate Reductase Respiratory Complex. Science, vol. 284, pp. 1961-1966
  • Janausch, 2001. Rekonstitution des Fumaratsensors DcuS in Liposomen und Transport von Fumarat und Succinat in Escherichia coli. Doctoral dissertation at Johannes Gutenberg-Universität Mainz, Germany
  • Gottschalk et al., 1986. Bacterial Metabolism. Springer-Verlag, New York, Berlin, Heidelberg, Tokyo
  • Park et al., 1999. Utilization of Electrically Reduced Neutral Red byActinobacillus succinogenes: Physiological Function of Neutral Red in Membrane-Driven Fumarate Reduction and Energy Conservation. Journal of Bacteriology, vol. 181, pp. 2403-2410
  • Richardson et al., 1999. Bacterial respiration: a flexible process for a changing environment. Microbiology, vol. 146, pp. 551-571
  • Unden et al., 1997. Alternative respiratory pathways of Escherichia coli: energetics and transcriptional regulation in response to electron acceptors. Biochimica et Biophysica Acta, vol. 1320, pp. 217-234
  • Stycharz, S. M., Glaven, R. H., Coppi, M. V., Gannon, S. M., Perpetua, L. A., Liu, A., Nevin, K. P. &amp. Lovley, D. R. (2011):Gene expression and deletion analysis of mechanisms for electron transfer from electrodes to Geobacter sulfurreducens. In: Bioelectrochemistry 80, pp. 142 - 150.
  • Dantas, J. M., Tomaz, D. M., Morgado, L. & Salgueiro, C. A.(2013): Functional charcterization of PccH, a key cytochrome for electron transfer from electrodes to the bacteium Geobacter sulfurreducens. In: FEBS Letters 587, pp. 2662 - 2668.
  • Jensen, H. M., Albers, A. E., Malley, K. R., Londer, Y. Y., Cohen, B. E., Helms, B. A., Weigele, P., Groves, J. T., Ajo-Franklin, C. M. (2010): Engineering of a synthetic electron conduit in living cells. In: PNAS 107, pp. 19213–19218.

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