VHb (hemoglobin)

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Vitreoscilla haemoglobin (VHb) is a type of haemoglobin found in the Gram-negative aerobic bacterium, Vitreoscilla . It is the first haemoglobin discovered from bacteria, but unlike classic haemoglobin it is composed only of a single globin molecule. [1] Like typical haemoglobin, its primary role is binding oxygen, but it also performs other functions including delivery of oxygen to oxygenases, detoxification of nitric oxide, sensing and relaying oxygen concentrations, peroxidase-like activity by eliminating autoxidation-derived H2O2 that prevents haeme degradation and iron release. [2]

Contents

Discovery

In 1986, a bacterial (Vitreoscilla) heme protein that had been studied by Webster and his colleagues, was sequenced and this amino acid sequence exhibited the globin folds of a haemoglobin. [3] [4] It consists of a single domain which normally occurs as a dimer. The solution of its crystal structure confirmed that its 3-dimensional structure is remarkably similar to the classic globin fold. [5] When the gene (vgb) for this haemoglobin was cloned into E. coli [6] it was found that it increased the growth of these cells under low oxygen conditions compared to control bacteria. [7] The concentration of VHb drastically increased in Vitreoscilla, a strict aerobe, grown under hypoxic conditions, [8] and it was proposed that it acted as an "oxygen storage trap" to feed oxygen to the terminal oxidase (cytochrome bo) under these conditions. [9] Further evidence for this is that VHb is concentrated in vivo near the membrane of Vitreoscilla cells. [10] It was also shown that VHb binds to subunit I of the cytochrome bo terminal oxidase, [11] the heme-containing subunit that is also responsible for the unique sodium pumping function of this unique terminal oxidase. [12]

Function

VHb is the best understood of all the bacterial haemoglobins, and is attributed to play a number of functions. Its main role is likely the binding of oxygen at low concentrations and its direct delivery to the terminal respiratory oxidase(s) such as cytochrome o. It is also involved in the delivery of oxygen to oxygenases, [13] detoxification of nitric oxide by converting it to nitrate, [14] and sensing oxygen concentrations and passing this signal to transcription factors. [15] [16] It has a peroxidase-like activity and effectively eliminates autoxidation-derived H2O2, which is a cause of haeme degradation and iron release. [2]

Genetic regulation

The VHb gene, vgb, exists as a single copy in Vitreoscilla and exhibits complete agreement with the primary sequence of VHb. [6] [17] The downstream region adjacent to vgb carries a gene in the opposite direction having close similarity with the uvrA gene of E. coli, indicating that vgb is not part of a multigene operon. [18] Biosynthesis of VHb is regulated at the transcriptional level and is induced under hypoxia in its native host. [19] vgb is expressed strongly in E. coli through its native promoter and a similar increase in its transcript level occurs under hypoxia; this suggests a close similarity in the transcriptional machinery of Vitreoscilla and E. coli. [20] The promoter region of vgb is crowded with overlapping binding sites for several redox-sensitive transcriptional regulators, involving the fumarate and nitrate reduction (Fnr) system as primary regulator. [15] The catabolite repression (Crp) system is an additional control [21] along with the aerobic respiration control (Arc) system as a third oxygen-dependent controller. [22] Another binding site for the oxidative stress response regulator (OxyR) is also present within the vgb promoter; all these transcriptional regulators appear to work in coordination with each other to control the biosynthesis of VHb in a redox dependent manner. [15]

Genetic engineering and applications

Since it was shown that VHb stimulated the growth of E. coli under hypoxic conditions, vgb was cloned into a variety of organisms, including various bacteria, yeast, fungi, and even higher plants and animals to test its effects on growth and production of products of potential commercial importance, the degradation of toxic compounds, the enhancement of nitrification in wastewater treatment, and other environmental applications. [23]

Examples of increased productivity include increased yield of a variety of biochemicals including antibiotics, an insecticide, a surfactant, and potential plastic feedstocks. They also include enzymes [24] (including one which might have anti-leukemic properties), and fuels (including ethanol, [25] butanediol, [26] [27] and biodiesel [28] ). The toxic compounds studied have been aromatics including 2-chlorobenzoic acid and 2,4-dinitrotolene. [29] [30] In these cases, increases in degradation are thought to be due both to the effects of VHb enhancing respiration to provide cells with additional ATP for growth and production of degrading enzymes, and delivery of oxygen directly to the oxygenases required for early steps in the degradative pathways.

Other environmental investigations include those related to heavy metal remediation and provision of soil phosphate to plants. [28] Expression of vgb in Nitrosomonas europaea , a bacterium involved of conversion of ammonia to nitrite in wastewater, enhanced, to some degree, its ability in this conversion. [31] Furthermore, it was shown that the mechanism of haeme protein expression to enhance oxygen supply to the monooxygenase in nitrification under hypoxic conditions is similar to VHb function seen in other applications. [32]

Amino acid residues in several sections of VHb in proximity to the haeme were altered using genetic engineering to change VHb’s affinity for oxygen and to examine the effects on the biotechnological properties of some of the systems studied. [23] Many of the mutations did not have large effects on the ligand binding properties of VHb, or provided at best a modest increase in cell growth compared with cells harboring wild type VHb. [23] [33] Two of the mutant VHb’s, however, provided substantial increases in growth and aromatic compound degradation compared to wild type VHb in Pseudomonas and Burkholderia bacteria transformed to contain vgb. [34]

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References

  1. ↑ Stark BC, Dikshit KL, Pagilla KR (2012). "The Biochemistry of Vitreoscilla hemoglobin". Computational and Structural Biotechnology Journal. 3 (4): e201210002. doi:10.5936/csbj.201210002. PMC   3962134 . PMID   24688662.
  2. 1 2 Isarankura-Na-Ayudhya C, Tansila N, Worachartcheewan A, Bülow L, Prachayasittikul V (2010). "Biochemical and cellular investigation of Vitreoscilla hemoglobin (VHb) variants possessing efficient peroxidase activity". J Microbiol Biotechnol. 20 (3): 532–541. PMID   20372024.
  3. ↑ Webster DA, Dikshit KL, Pagilla KR, Stark BC (August 2021). "The Discovery of Vitreoscilla Hemoglobin and Early Studies on Its Biochemical Functions, the Control of Its Expression, and Its Use in Practical Applications". Microorganisms. 9 (8): 1637. doi: 10.3390/microorganisms9081637 . ISSN   2076-2607. PMC   8398370 . PMID   34442716.
  4. ↑ Wakabayashi S, Matsubara H, Webster DA (July 1986). "Primary sequence of a dimeric bacterial haemoglobin from Vitreoscilla". Nature. 322 (6078): 481–483. Bibcode:1986Natur.322..481W. doi:10.1038/322481a0. ISSN   1476-4687. PMID   3736670.
  5. ↑ Tarricone C, Galizzi A, Coda A, Ascenzi P, Bolognesi M (April 1997). "Unusual structure of the oxygen-binding site in the dimeric bacterial hemoglobin from Vitreoscilla sp". Structure. 5 (4): 497–507. doi: 10.1016/s0969-2126(97)00206-2 . ISSN   0969-2126. PMID   9115439.
  6. 1 2 Dikshit KL, Webster DA (1988-10-30). "Cloning, characterization and expression of the bacterial globin gene from Vitreoscilla in Escherichia coli". Gene. 70 (2): 377–386. doi:10.1016/0378-1119(88)90209-0. ISSN   0378-1119. PMID   2850971.
  7. ↑ Webster DA, Dikshit KL, Pagilla KR, Stark BC (October 2021). "The Discovery of Vitreoscilla Hemoglobin and Early Studies on Its Biochemical Functions, the Control of Its Expression, and Its Use in Practical Applications". Microorganisms. 9 (8): 1637. doi: 10.3390/microorganisms9081637 . ISSN   2076-2607. PMC   8398370 . PMID   34442716.
  8. ↑ Boerman SJ, Webster DA (1982). "Control of Heme Content in Vitreoscilla by Oxygen". The Journal of General and Applied Microbiology. 28 (1): 35–43. doi:10.2323/jgam.28.35.
  9. ↑ Webster DA (1988). "Structure and function of bacterial hemoglobin and related proteins". Advances in Inorganic Biochemistry. 7: 245–265. PMID   3275422.
  10. ↑ Ramandeep, Hwang KW, Raje M, Kim KJ, Stark BC, Dikshit KL, Webster DA (January 2001). "Vitreoscilla Hemoglobin". Journal of Biological Chemistry. 276 (27): 24781–24789. doi: 10.1074/jbc.m009808200 . ISSN   0021-9258. PMID   11331274.
  11. ↑ Park KW, Kim KJ, Howard AJ, Stark BC, Webster DA (September 2002). "Vitreoscilla Hemoglobin Binds to Subunit I of Cytochrome bo Ubiquinol Oxidases". Journal of Biological Chemistry. 277 (36): 33334–33337. doi: 10.1074/jbc.m203820200 . ISSN   0021-9258. PMID   12080058.
  12. ↑ Chung YT, Stark BC, Webster DA (2006-10-06). "Role of Asp544 in subunit I for Na+ pumping by Vitreoscilla cytochrome bo". Biochemical and Biophysical Research Communications. 348 (4): 1209–1214. doi:10.1016/j.bbrc.2006.07.184. ISSN   0006-291X. PMID   16919598.
  13. ↑ Fish PA, Webster DA, Stark BC (2000-03-20). "Vitreoscilla hemoglobin enhances the first step in 2,4-dinitrotoluene degradation in vitro and at low aeration in vivo". Journal of Molecular Catalysis B: Enzymatic. 9 (1): 75–82. doi:10.1016/S1381-1177(99)00086-7. ISSN   1381-1177.
  14. ↑ Kaur R, Pathania R, Sharma V, Mande SC, Dikshit KL (January 2002). "Chimeric Vitreoscilla Hemoglobin (VHb) Carrying a Flavoreductase Domain Relieves Nitrosative Stress in Escherichia coli : New Insight into the Functional Role of VHb". Applied and Environmental Microbiology. 68 (1): 152–160. Bibcode:2002ApEnM..68..152K. doi:10.1128/AEM.68.1.152-160.2002. ISSN   0099-2240. PMC   126558 . PMID   11772621.
  15. 1 2 3 Anand A, Duk BT, Singh S, Akbas MY, Webster DA, Stark BC, Dikshit KL (2010-02-24). "Redox-mediated interactions of VHb (Vitreoscilla haemoglobin) with OxyR: novel regulation of VHb biosynthesis under oxidative stress". Biochemical Journal. 426 (3): 271–280. doi:10.1042/bj20091417. ISSN   0264-6021. PMID   20025616.
  16. ↑ Stark BC, Dikshit KL, Pagilla KR (2011). "Recent advances in understanding the structure, function, and biotechnological usefulness of the hemoglobin from the bacterium Vitreoscilla". Biotechnol Lett. 33 (9): 1705–1714. doi:10.1007/s10529-011-0621-9. PMID   21603987.
  17. ↑ Webster DA, Dikshit KL, Pagilla KR, Stark BC (2021). "The Discovery of Vitreoscilla Hemoglobin and Early Studies on Its Biochemical Functions, the Control of Its Expression, and Its Use in Practical Applications". Microorganisms. 9 (8): 1637. doi: 10.3390/microorganisms9081637 . ISSN   2076-2607. PMC   8398370 . PMID   34442716.
  18. ↑ Liu SC, Liu YX, Webster DA, Stark BC (November 1994). "Sequence of the region downstream of the Vitreoscilla hemoglobin gene: vgb is not part of a multigene operon". Applied Microbiology and Biotechnology. 42 (2): 304–308. doi:10.1007/BF00902733. ISSN   1432-0614. PMID   7765771.
  19. ↑ Dikshit KL, Spaulding D, Braun A, Webster DA (1989). "Oxygen Inhibition of Globin Gene Transcription and Bacterial Haemoglobin Synthesis in Vitreoscilla". Microbiology. 135 (10): 2601–2609. doi: 10.1099/00221287-135-10-2601 . ISSN   1465-2080. PMID   2483729.
  20. ↑ Dikshit KL, Dikshit RP, Webster DA (1990-07-25). "Study of Vitreoscilla globin(vgb) gene expression and promoter activity in E. Coli through transcriptional fusion". Nucleic Acids Research. 18 (14): 4149–4155. doi: 10.1093/nar/18.14.4149 . ISSN   0305-1048. PMC   331172 . PMID   2198533.
  21. ↑ Joshi M, Dikshit KL (1994-07-15). "Oxygen-Dependent Regulation of Vitreoscilla Globin Gene: Evidence for Positive Regulation by FNR". Biochemical and Biophysical Research Communications. 202 (1): 535–542. doi:10.1006/bbrc.1994.1961. ISSN   0006-291X. PMID   8037759.
  22. ↑ Yang J, Webster DA, Stark BC (2005-10-03). "ArcA works with Fnr as a positive regulator of Vitreoscilla (bacterial) hemoglobin gene expression in Escherichia coli". Microbiological Research. 160 (4): 405–415. doi: 10.1016/j.micres.2005.03.004 . ISSN   0944-5013. PMID   16255146.
  23. 1 2 3 Stark BC, Pagilla KR, Dikshit KL (2015-02-01). "Recent applications of Vitreoscilla hemoglobin technology in bioproduct synthesis and bioremediation". Applied Microbiology and Biotechnology. 99 (4): 1627–1636. doi:10.1007/s00253-014-6350-y. ISSN   1432-0614. PMID   25575886.
  24. ↑ Khosravi M, Webster DA, Stark BC (November 1990). "Presence of the bacterial hemoglobin gene improves α-amylase production of a recombinant Escherichia coli strain". Plasmid. 24 (3): 190–194. doi:10.1016/0147-619X(90)90002-T. ISSN   0147-619X. PMID   2136531.
  25. ↑ Sanny T, Arnaldos M, Kunkel SA, Pagilla KR, Stark BC (November 2010). "Engineering of ethanolic E. coli with the Vitreoscilla hemoglobin gene enhances ethanol production from both glucose and xylose". Applied Microbiology and Biotechnology. 88 (5): 1103–1112. doi:10.1007/s00253-010-2817-7. ISSN   1432-0614. PMID   20717665.
  26. ↑ Wei ML, Webster DA, Stark BC (1998-09-05). "Metabolic engineering of Serratia marcescens with the bacterial hemoglobin gene: Alterations in fermentation pathways". Biotechnology and Bioengineering. 59 (5): 640–646. doi:10.1002/(SICI)1097-0290(19980905)59:5<640::AID-BIT15>3.0.CO;2-D. PMID   10099382.
  27. ↑ Geckil H, Barak Z, Chipman DM, Erenler SO, Webster DA, Stark BC (October 2004). "Enhanced production of acetoin and butanediol in recombinant Enterobacter aerogenes carrying Vitreoscilla hemoglobin gene". Bioprocess and Biosystems Engineering. 26 (5): 325–330. doi:10.1007/s00449-004-0373-1. ISSN   1615-7605. PMID   15309606.
  28. 1 2
  29. ↑ Urgun-Demirtas M, Pagilla KR, Stark BC, Webster D (October 2003). "Biodegradation of 2-Chlorobenzoate by Recombinant Burkholderia Cepacia Expressing Vitreoscilla Hemoglobin Under Variable Levels of Oxygen Availability". Biodegradation. 14 (5): 357–365. doi:10.1023/A:1025672528291. ISSN   1572-9729. PMID   14571952.
  30. ↑ So J, Webster DA, Stark BC, Pagilla KR (2004-06-01). "Enhancement of 2,4-dinitrotoluene biodegradation by Burkholderia sp. in sand bioreactors using bacterial hemoglobin technology". Biodegradation. 15 (3): 161–171. doi:10.1023/B:BIOD.0000026496.38594.b2. ISSN   1572-9729. PMID   15228074.
  31. ↑ Kunkel SA, Pagilla KR, Stark BC (2015-08-01). "Engineering of Nitrosomonas europaea to express Vitreoscilla hemoglobin enhances oxygen uptake and conversion of ammonia to nitrite". AMB Express. 5 (1): 43. doi: 10.1186/s13568-015-0135-2 . ISSN   2191-0855. PMC   4522006 . PMID   26231847.
  32. ↑ Arnaldos M, Kunkel SA, Stark BC, Pagilla KR (2014-04-01). "Characterization of heme protein expressed by ammonia-oxidizing bacteria under low dissolved oxygen conditions". Applied Microbiology and Biotechnology. 98 (7): 3231–3239. doi:10.1007/s00253-013-5400-1. ISSN   1432-0614. PMID   24272370.
  33. ↑ Kaur R, Ahuja S, Anand A, Singh B, Stark BC, Webster DA, Dikshit KL (2008-10-15). "Functional implications of the proximal site hydrogen bonding network in Vitreoscilla hemoglobin (VHb): Role of Tyr95 (G5) and Tyr126 (H12)". FEBS Letters. 582 (23–24): 3494–3500. Bibcode:2008FEBSL.582.3494K. doi:10.1016/j.febslet.2008.09.018. ISSN   0014-5793. PMID   18804465.
  34. ↑ Kim Y, Webster DA, Stark BC (2005). "Improvement of bioremediation by Pseudomonas and Burkholderia by mutants of the Vitreoscilla hemoglobin gene (vgb) integrated into their chromosomes". Journal of Industrial Microbiology & Biotechnology. 32 (4): 148–154. doi:10.1007/s10295-005-0215-4. ISSN   1367-5435. PMID   15806390.
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