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Abstract
Modified tetrapyrroles are large macrocyclic compounds, consisting of diverse conjugation and metal chelation systems and imparting an array of colors to the biological structures that contain them. Tetrapyrroles represent some of the most complex small molecules synthesized by cells and are involved in many essential processes that are fundamental to life on Earth, including photosynthesis, respiration, and catalysis. These molecules are all derived from a common template through a series of enzyme-mediated transformations that alter the oxidation state of the macrocycle and also modify its size, its side-chain composition, and the nature of the centrally chelated metal ion. The different modified tetrapyrroles include chlorophylls, hemes, siroheme, corrins (including vitamin B12), coenzyme F430, heme d1, and bilins. After nearly a century of study, almost all of the more than 90 different enzymes that synthesize this family of compounds are now known, and expression of reconstructed operons in heterologous hosts has confirmed that most pathways are complete. Aside from the highly diverse nature of the chemical reactions catalyzed, an interesting aspect of comparative biochemistry is to see how different enzymes and even entire pathways have evolved to perform alternative chemical reactions to produce the same end products in the presence and absence of oxygen. Although there is still much to learn, our current understanding of tetrapyrrole biogenesis represents a remarkable biochemical milestone that is summarized in this review.
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Affiliation(s)
- Donald A Bryant
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717
| | - C Neil Hunter
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, United Kingdom
| | - Martin J Warren
- School of Biosciences, University of Kent, Canterbury CT2 7NJ, United Kingdom
- Quadram Institute Bioscience, Norwich Research Park, Norwich NR4 7UQ, United Kingdom
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Gopinath K, Moosa A, Mizrahi V, Warner DF. Vitamin B(12) metabolism in Mycobacterium tuberculosis. Future Microbiol 2014; 8:1405-18. [PMID: 24199800 DOI: 10.2217/fmb.13.113] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Mycobacterium tuberculosis is included among a select group of bacteria possessing the capacity for de novo biosynthesis of vitamin B12, the largest and most complex natural organometallic cofactor. The bacillus is also able to scavenge B12 and related corrinoids utilizing an ATP-binding cassette-type protein that is distinct from the only known bacterial B12-specific transporter, BtuFCD. Consistent with the inferred requirement for vitamin B12 for metabolic function, the M. tuberculosis genome encodes two B12 riboswitches and three B12-dependent enzymes. Two of these enzymes have been shown to operate in methionine biosynthesis (MetH) and propionate utilization (MutAB), while the function of the putative nrdZ-encoded ribonucleotide reductase remains unknown. Taken together, these observations suggest that M. tuberculosis has the capacity to regulate core metabolic functions according to B12 availability - whether acquired via endogenous synthesis or through uptake from the host environment - and, therefore, imply that there is a role for vitamin B12 in pathogenesis, which remains poorly understood.
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Affiliation(s)
- Krishnamoorthy Gopinath
- MRC/NHLS/UCT Molecular Mycobacteriology Research Unit & DST/NRF Center of Excellence for Biomedical TB Research, Institute of Infectious Disease & Molecular Medicine & Department of Clinical Laboratory Sciences, Faculty of Health Sciences, University of Cape Town, Observatory 7925, Cape Town, South Africa
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Deery E, Schroeder S, Lawrence AD, Taylor SL, Seyedarabi A, Waterman J, Wilson KS, Brown D, Geeves MA, Howard MJ, Pickersgill RW, Warren MJ. An enzyme-trap approach allows isolation of intermediates in cobalamin biosynthesis. Nat Chem Biol 2012; 8:933-40. [PMID: 23042036 PMCID: PMC3480714 DOI: 10.1038/nchembio.1086] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2012] [Accepted: 09/05/2012] [Indexed: 11/16/2022]
Abstract
The biosynthesis of many vitamins and coenzymes has often proved difficult to elucidate due to a combination of low abundance and kinetic lability of the pathway intermediates. Through a serial reconstruction of the cobalamin (vitamin B12) pathway in E. coli, and by His-tagging the terminal enzyme in the reaction sequence, we have observed that many unstable intermediates can be isolated as tightly-bound enzyme-product complexes. Together, these approaches have been used to extract intermediates between precorrin-4 and hydrogenobyrinic acid in their free acid form and permitted the delineation of the overall reaction catalysed by CobL, including the formal elucidation of precorrin-7 as a metabolite. Furthermore, a substrate-carrier protein, CobE, has been identified, which can also be used to stabilize some of the transient metabolic intermediates and enhance their onward transformation. The tight association of pathway intermediates with enzymes provides evidence for a form of metabolite channeling.
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Affiliation(s)
- Evelyne Deery
- School of Biosciences, University of Kent, Canterbury, Kent, UK
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Battersby AR. New intermediates in the B12 pathway. CIBA FOUNDATION SYMPOSIUM 2007; 180:267-79; discussion 280-4. [PMID: 7842858 DOI: 10.1002/9780470514535.ch15] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Vitamin B12 has a complex structure which represents one of the most challenging biosynthetic problems in Nature. Exciting progress has been made by combining the techniques, approaches and strengths of chemistry, spectroscopy and biology. Most of the advances until recently came from experiments based either on labelling simpler precursors with radioactive isotopes followed by controlled degradation of the labelled products, or on the use of stable isotopes, 13C in particular, because it can be detected and its environment can be studied by NMR spectroscopy. These experiments imposed heavy demands on synthesis which provided the specifically labelled starting materials. More recently, the powerful methods of genetics and molecular biology have been added to the armoury, leading to another massive surge forward by allowing the preparation, through gene overexpression, of large quantities of the enzymes of the biosynthetic pathway. Equally important has been the generation of mutant forms of B12-producing organisms in which the biosynthetic pathway is blocked at specific points. Here I focus on the latest advances. The structures of the newly discovered intermediates are described and some of the chemistry involved is explored. In conclusion, the presently known pathway to vitamin B12 is reviewed.
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Scott AI. Recent studies of enzymically controlled steps in B12 biosynthesis. CIBA FOUNDATION SYMPOSIUM 2007; 180:285-303; discussion 303-8. [PMID: 7842859 DOI: 10.1002/9780470514535.ch16] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The acquisition and sequencing of the genes encoding the enzymes for vitamin B12 biosynthesis in Salmonella typhimurium and Pseudomonas denitrificans has dramatically altered the direction of research on the pathway from uroporphyrinogen III to the corrinoids. Through a combination of molecular biology, organic chemistry and NMR spectroscopy, logical progression along the sequence is being made. Recent work from our laboratory is focused on the discovery and specificities of the methyltransferases connecting uroporphyrinogen III with cobyrinic acid, the temporal resolution of cobalt insertion and a comparison of the anaerobic pathway in S. typhimurium and the aerobic pathway in Ps. denitrificans. The implication of two parallel routes to corrins in these bacteria is discussed.
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Affiliation(s)
- A I Scott
- Department of Chemistry, Texas A&M University, College Station 77843-3255
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Scott AI, Roessner CA. Recent discoveries in the pathways to cobalamin (coenzyme B12) achieved through chemistry and biology. PURE APPL CHEM 2007. [DOI: 10.1351/pac200779122179] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The genetic engineering of Escherichia coli for the over-expression of enzymes of the aerobic and anaerobic pathways to cobalamin has resulted in the in vivo and in vitro biosynthesis of new intermediates and other products that were isolated and characterized using a combination of bioorganic chemistry and high-resolution NMR. Analyses of these products were used to deduct the functions of the enzymes that catalyze their synthesis. CobZ, another enzyme for the synthesis of precorrin-3B of the aerobic pathway, has recently been described, as has been BluB, the enzyme responsible for the oxygen-dependent biosynthesis of dimethylbenzimidazole. In the anaerobic pathway, functions have recently been experimentally confirmed for or assigned to the CbiMNOQ cobalt transport complex, CbiA (a,c side chain amidation), CbiD (C-1 methylation), CbiF (C-11 methylation), CbiG (lactone opening, deacylation), CbiP (b,d,e,g side chain amidation), and CbiT (C-15 methylation, C-12 side chain decarboxylation). The dephosphorylation of adenosylcobalamin-phosphate, catalyzed by CobC, has been proposed as the final step in the biosynthesis of adenosylcobalamin.
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Affiliation(s)
- A. Ian Scott
- 1Center for Biological NMR, Department of Chemistry, Texas A and M University, College Station, TX 77843-3255, USA
| | - Charles A. Roessner
- 1Center for Biological NMR, Department of Chemistry, Texas A and M University, College Station, TX 77843-3255, USA
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Roessner CA, Scott AI. Fine-tuning our knowledge of the anaerobic route to cobalamin (vitamin B12). J Bacteriol 2006; 188:7331-4. [PMID: 16936030 PMCID: PMC1636268 DOI: 10.1128/jb.00918-06] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Affiliation(s)
- Charles A Roessner
- Department of Chemistry, Center for Biological NMR, Texas A&M University, College Station, 77843-3255, USA.
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Abstract
The chronology of the discoveries along the pathway of vitamin B(12) biosynthesis is reviewed from a personal perspective, including discussion of the most recent finding that two pathways to B(12) exist-one aerobic and one anaerobic-which differ mainly in the ring contraction mechanisms that convert porphyrin to corrin.
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Affiliation(s)
- A Ian Scott
- Center for Biological NMR, Chemistry Department, Texas A&M University, 3255 TAMU, College Station, Texas 77843-3255, USA.
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9
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Abstract
The chronology of the discoveries along the pathway of vitamin B12 biosynthesis is reviewed from a personal perspective, including discussion of the most recent finding that two pathways to B12 exist--one aerobic and one anaerobic--which differ mainly in the ring contraction mechanisms which convert porphyrin to corrin.
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Affiliation(s)
- A I Scott
- Center for Biological NMR, Chemistry Department, Texas A&M University, College Station 77843-3255, USA.
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Roessner CA, Santander PJ, Scott AI. Multiple biosynthetic pathways for vitamin B12: variations on a central theme. VITAMINS AND HORMONES 2001; 61:267-97. [PMID: 11153269 DOI: 10.1016/s0083-6729(01)61009-4] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
The manner in which vitamin B12 is synthesized is detailed with emphasis on the different mechanisms for ring contraction encountered in aerobic and anaerobic organisms. The aerobic process utilizes two enzymes and is dependent on molecular oxygen, in stark contrast to the anaerobic mechanism which is controlled by cobalt and requires only one enzyme.
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Affiliation(s)
- C A Roessner
- Center for Biological NMR, Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA
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Raux E, Schubert HL, Roper JM, Wilson KS, Warren MJ. Vitamin B12: Insights into Biosynthesis's Mount Improbable. Bioorg Chem 1999. [DOI: 10.1006/bioo.1998.1125] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Raux E, Thermes C, Heathcote P, Rambach A, Warren MJ. A role for Salmonella typhimurium cbiK in cobalamin (vitamin B12) and siroheme biosynthesis. J Bacteriol 1997; 179:3202-12. [PMID: 9150215 PMCID: PMC179098 DOI: 10.1128/jb.179.10.3202-3212.1997] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The role of cbiK, a gene found encoded within the Salmonella typhimurium cob operon, has been investigated by studying its in vivo function in Escherichia coli. First, it was found that cbiK is not required for cobalamin biosynthesis in the presence of a genomic cysG gene (encoding siroheme synthase) background. Second, in the absence of a genomic cysG gene, cobalamin biosynthesis in E. coli was found to be dependent upon the presence of cobA(P. denitrificans) (encoding the uroporphyrinogen III methyltransferase from Pseudomonas denitrificans) and cbiK. Third, complementation of the cysteine auxotrophy of the E. coli cysG deletion strain 302delta a could be attained by the combined presence of cobA(P. denitrificans) and the S. typhimurium cbiK gene. Collectively these results suggest that CbiK can function in fashion analogous to that of the N-terminal domain of CysG (CysG(B)), which catalyzes the final two steps in siroheme synthesis, i.e., NAD-dependent dehydrogenation of precorrin-2 to sirohydrochlorin and ferrochelation. Thus, phenotypically CysG(B) and CbiK have very similar properties in vivo, although the two proteins do not have any sequence similarity. In comparison to CysG, CbiK appears to have a greater affinity for Co2+ than for Fe2+, and it is likely that cbiK encodes an enzyme whose primary role is that of a cobalt chelatase in corrin biosynthesis.
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Affiliation(s)
- E Raux
- Department of Molecular Genetics, Institute of Ophthalmology, University College London, United Kingdom
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Wang J, Stolowich NJ, Santander PJ, Park JH, Scott AI. Biosynthesis of vitamin B12: concerning the identity of the two-carbon fragment eliminated during anaerobic formation of cobyrinic acid. Proc Natl Acad Sci U S A 1996; 93:14320-2. [PMID: 8962048 PMCID: PMC26129 DOI: 10.1073/pnas.93.25.14320] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
It has been proved that, during anaerobic biosynthesis of the corrin macrocycle, the two-carbon fragment excised from the precursor, precorrin-3, is acetaldehyde, which originates from C-20 and its attached methyl group. This apparently contradictory finding is rationalized in terms of the subsequent enzymatic oxidation of acetaldehyde to acetic acid, which was previously regarded as the volatile fragment released by the action of the biosynthetic enzymes of Propionibacterium shermanii. The observation that acetaldehyde (rather than acetic acid) is extruded during anaerobic B12 synthesis is in full accord with the structure of factor IV, a new intermediate on the pathway.
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Affiliation(s)
- J Wang
- Department of Chemistry, Texas A&M University, College Station 77843, USA
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Roessner CA, Scott AI. Genetically engineered synthesis of natural products: from alkaloids to corrins. Annu Rev Microbiol 1996; 50:467-90. [PMID: 8905088 DOI: 10.1146/annurev.micro.50.1.467] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Because many natural products are of biological and medicinal importance, methods are continually being sought for studying their biosynthetic pathways, which may eventually result in increased production and the generation of novel compounds. Advances in genetic engineering have enabled the homologous or heterologous expression of many natural product biosynthetic genes from divergent sources, resulting in a supply of enzymes not readily available by isolation from the producing organism. Mixing and matching of these enzymes in cell-free reactions can provide information, not available by any other means, about enzyme mechanisms, pathway intermediates, and possible variations in the structure of the final product.
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Affiliation(s)
- C A Roessner
- Department of Chemistry, Texas A&M University, College Station 77843-3255, USA
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Roessner CA, Scott AI. Achieving natural product synthesis and diversity via catalytic networking ex vivo. CHEMISTRY & BIOLOGY 1996; 3:325-30. [PMID: 8807860 DOI: 10.1016/s1074-5521(96)90114-3] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Recent studies on ex vivo synthesis of natural products reveal that even complex multistep pathways can be successfully reconstructed. Genetic engineering of such reconstituted pathways has already been used to generate 'unnatural' natural products related to the original compound. In the future, it may be possible to use these approaches to make natural products that are currently inaccessible to conventional synthesis.
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Affiliation(s)
- C A Roessner
- Center for Biological NMR, Department of Chemistry, Texas A&M University, College Station, TX 77843-3255, USA
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Stolowich NJ, Wang J, Spencer JB, Santander PJ, Roessner CA, Scott AI. Absolute Stereochemistry of Precorrin-3x and Its Relevance to the Dichotomy of Ring Contraction Mechanism in Vitamin B12 Biosynthesis. J Am Chem Soc 1996. [DOI: 10.1021/ja952739s] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Neal J. Stolowich
- Contribution from the Center for Biological NMR, Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255
| | - Jianji Wang
- Contribution from the Center for Biological NMR, Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255
| | - Jonathan B. Spencer
- Contribution from the Center for Biological NMR, Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255
| | - Patricio J. Santander
- Contribution from the Center for Biological NMR, Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255
| | - Charles A. Roessner
- Contribution from the Center for Biological NMR, Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255
| | - A. Ian Scott
- Contribution from the Center for Biological NMR, Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255
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Sattler I, Roessner CA, Stolowich NJ, Hardin SH, Harris-Haller LW, Yokubaitis NT, Murooka Y, Hashimoto Y, Scott AI. Cloning, sequencing, and expression of the uroporphyrinogen III methyltransferase cobA gene of Propionibacterium freudenreichii (shermanii). J Bacteriol 1995; 177:1564-9. [PMID: 7883713 PMCID: PMC176773 DOI: 10.1128/jb.177.6.1564-1569.1995] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
We cloned, sequenced, and overexpressed cobA, the gene encoding uroporphyrinogen III methyltransferase in Propionibacterium freudenreichii, and examined the catalytic properties of the enzyme. The methyltransferase is similar in mass (27 kDa) and homologous to the one isolated from Pseudomonas denitrificans. In contrast to the much larger isoenzyme encoded by the cysG gene of Escherichia coli (52 kDa), the P. freudenreichii enzyme does not contain the additional 22-kDa peptide moiety at its N-terminal end bearing the oxidase-ferrochelatase activity responsible for the conversion of dihydrosirohydrochlorin (precorrin-2) to siroheme. Since it does not contain this moiety, it is not a likely candidate for synthesis of a cobalt-containing early intermediate that has been proposed for the vitamin B12 biosynthetic pathway in P. freudenreichii. Uroporphyrinogen III methyltransferase of P. freudenreichii not only catalyzes the addition of two methyl groups to uroporphyrinogen III to afford the early vitamin B12 intermediate, precorrin-2, but also has an overmethylation property that catalyzes the synthesis of several tri- and tetra-methylated compounds that are not part of the vitamin B12 pathway. The enzyme catalyzes the addition of three methyl groups to uroporphyrinogen I to form trimethylpyrrocorphin, the intermediate necessary for biosynthesis of the natural products, factors S1 and S3, previously isolated from this organism. A second gene found upstream from the cobA gene encodes a protein homologous to CbiO of Salmonella typhimurium, a membrane-bound, ATP-dependent transport protein thought to be part of the cobalt transport system involved in vitamin B12 synthesis. These two genes do not appear to constitute part of an extensive cobalamin operon.
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Affiliation(s)
- I Sattler
- Center for Biological NMR, Chemistry Department, Texas A&M University, College Station 77843
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Blanche F, Cameron B, Crouzet J, Debussche L, Thibaut D, Vuilhorgne M, Leeper FJ, Battersby AR. Vitamin B12: Wie das Problem seiner Biosynthese gelöst wurde. Angew Chem Int Ed Engl 1995. [DOI: 10.1002/ange.19951070404] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Roessner CA, Spencer JB, Stolowich NJ, Wang J, Nayar GP, Santander PJ, Pichon C, Min C, Holderman MT, Scott AI. Genetically engineered synthesis of precorrin-6x and the complete corrinoid, hydrogenobyrinic acid, an advanced precursor of vitamin B12. CHEMISTRY & BIOLOGY 1994; 1:119-24. [PMID: 9383380 DOI: 10.1016/1074-5521(94)90050-7] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
BACKGROUND Genetically engineered synthesis, in which the gene products, cofactors, and substrates of a complete pathway are combined in vitro in a single flask to give the target, can be a viable alternative to conventional chemical construction of molecules of complex structure and stereochemistry. We chose to attempt to synthesize the metal-free corrinoid hydrogenobyrinic acid, an advanced precursor of vitamin B12. RESULTS Cloning and overexpression of the genes necessary for the S-adenosyl methionine dependent conversion of 5-aminolevulinic acid (ALA) to precorrin-3 and those required for the synthesis of hydrogenobyrinic acid from precorrin-3 completed the repertoire of the 12 biosynthetic enzymes involved in corrin synthesis. Using these enzymes and the necessary cofactors, the multi-enzyme synthesis of hydrogenobyrinic acid from ALA can be achieved in 20% overall yield in a single reaction vessel, corresponding to an average of at least 90% conversion for each of the 17 steps involved. CONCLUSIONS By replacing the cell wall with glass, and by mixing the soluble biosynthetic enzymes and necessary cofactors, the major segment of the physiological synthesis of vitamin B12 has been accomplished. Since only those enzymes necessary for the synthesis of hydrogenobyrinic acid from ALA are supplied, none of the intermediates is deflected from the direct pathway. This results in an efficiency which in fact surpasses that of nature.
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Affiliation(s)
- C A Roessner
- Department of Chemistry, Texas A&M University, College Station 77843-3255, USA
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Abstract
In part because humans cannot synthesize vitamin B12 and must obtain it from organisms that produce it and because B12 deficiency leads to pernicious anemia, it has been important to understand how microorganisms build this quite complex substance. As shown here, an interdisciplinary attack was needed, which combined the strengths of genetics, molecular biology, enzymology, chemistry, and spectroscopy. This allowed the step-by-step synthetic pathway of B12 to be elucidated, and this approach has acted as a model for future research on the synthesis of substances in living organisms. One practical outcome of such an approach has been the improved availability of B12 for animal feedstuffs and human health.
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