This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Synonyms: 1-butanol synthesis
|Superclasses:||Biosynthesis → Secondary Metabolites Biosynthesis → Alcohols Biosynthesis|
|Generation of Precursor Metabolites and Energy → Fermentation → Pyruvate Fermentation|
Note: This is an engineered pathway. It does not occur naturally in any known organism, and has been constructed in a living cell by metabolic engineering.
The enzymes catalyzing the steps of this pathway have been assembled from the following organisms : Clostridium acetobutylicum , Clostridium acetobutylicum ATCC 824 , Escherichia coli K-12 substr. MG1655 , Euglena gracilis
Biomass is gaining increasing attention as a renewable energy source due to environmental and energy concerns [Atsumi08]. n-butanol is a biomass product that has many advantages compared to ethanol as a substitute for gasoline because of its hydrophobicity and higher energy content. Clostridium acetobutylicum is a Gram-positive strict anaerobe and a key microbial producer of n-butanol [Lin83] (see pyruvate fermentation to butanol I). However, the concomitant synthesis of the byproducts butyrate, acetone and ethanol makes n-butanol production difficult to control experimentally [Jones86] (see superpathway of Clostridium acetobutylicum solventogenic fermentation). Furthermore, Clostridium acetobutylicum is a slow growing organism which is not as well understood as some other microorganisms, making it an arduous task to optimize n-butanol production [Atsumi08].
About this Pathway
The Clostridium n-butanol biosynthesis pathway was reconstructed in Escherichia coli, a well studied organism [Atsumi08]. The Clostridium acetobutylicum genes necessary to produce n-butanol from acetyl-CoA were introduced, and included acetyl-CoA C-acetyltransferase thl and aldehyde/alcohol dehydrogenase adhE2, 3-hydroxybutyryl-CoA dehydrogenase hbd, 3-hydroxybutyryl-CoA dehydratase crt and butyryl-CoA dehydrogenase/electron transfer flavoprotein bcd/etfAB.
To increase n-butanol production, the host genes that would compete with the n-butanol pathway for the precursor acetyl-CoA or the cofactor NADH were deleted. These included the genes ldhA, adhE and frdBC. Native adhE in E.coli was replaced with adhE2 from Clostridium acetobutylicum because adhE has higher activity towards acetyl-CoA than adhE2 [Atsumi08].
The enzyme mitochondrial trans-2-enoyl-CoA reductase (TER) from Euglena gracilis catalyzes the reaction of crotonyl-CoA to butanoyl-CoA [Tucci07]. In Clostridium acetobutylicum this reaction is perfomed by butyryl-CoA dehydrogenase bcd [Lan11], which also requires the expression of etfAB, an electron transfer flavoprotein (ETF) proposed to be involved in electron transfer to butyryl-CoA dehydrogenase [Woods93, Boynton96a]. mitochondrial trans-2-enoyl-CoA reductase performs better than Clostridium acetobutylicum Bcd-EtfAB complex by utilizing NADH as the reducing cofactor and making the reaction irreversible [BondWatts11].
Superpathways: 1-butanol autotrophic biosynthesis
Variants: pyruvate fermentation to acetate and alanine , pyruvate fermentation to acetate and lactate I , pyruvate fermentation to acetate and lactate II , pyruvate fermentation to acetate I , pyruvate fermentation to acetate II , pyruvate fermentation to acetate III , pyruvate fermentation to acetate IV , pyruvate fermentation to acetate V , pyruvate fermentation to acetate VI , pyruvate fermentation to acetate VII , pyruvate fermentation to acetate VIII , pyruvate fermentation to acetone , pyruvate fermentation to butanoate , pyruvate fermentation to butanol I , pyruvate fermentation to ethanol I , pyruvate fermentation to ethanol II , pyruvate fermentation to ethanol III , pyruvate fermentation to hexanol , pyruvate fermentation to isobutanol (engineered) , pyruvate fermentation to lactate , pyruvate fermentation to opines , pyruvate fermentation to propanoate I , pyruvate fermentation to propanoate II (acrylate pathway) , superpathway of Clostridium acetobutylicum acidogenic and solventogenic fermentation , superpathway of Clostridium acetobutylicum acidogenic fermentation , superpathway of Clostridium acetobutylicum solventogenic fermentation , superpathway of fermentation (Chlamydomonas reinhardtii)
Atsumi08: Atsumi S, Cann AF, Connor MR, Shen CR, Smith KM, Brynildsen MP, Chou KJ, Hanai T, Liao JC (2008). "Metabolic engineering of Escherichia coli for 1-butanol production." Metab Eng 10(6);305-11. PMID: 17942358
Boynton96a: Boynton ZL, Bennet GN, Rudolph FB (1996). "Cloning, sequencing, and expression of clustered genes encoding beta-hydroxybutyryl-coenzyme A (CoA) dehydrogenase, crotonase, and butyryl-CoA dehydrogenase from Clostridium acetobutylicum ATCC 824." J Bacteriol 1996;178(11);3015-24. PMID: 8655474
Acebron09: Acebron SP, Martin I, del Castillo U, Moro F, Muga A (2009). "DnaK-mediated association of ClpB to protein aggregates. A bichaperone network at the aggregate surface." FEBS Lett 583(18);2991-6. PMID: 19698713
Alber06: Alber BE, Spanheimer R, Ebenau-Jehle C, Fuchs G (2006). "Study of an alternate glyoxylate cycle for acetate assimilation by Rhodobacter sphaeroides." Mol Microbiol 61(2);297-309. PMID: 16856937
Aristarkhov96: Aristarkhov A, Mikulskis A, Belasco JG, Lin EC (1996). "Translation of the adhE transcript to produce ethanol dehydrogenase requires RNase III cleavage in Escherichia coli." J Bacteriol 178(14);4327-32. PMID: 8763968
Beloin04: Beloin C, Valle J, Latour-Lambert P, Faure P, Kzreminski M, Balestrino D, Haagensen JA, Molin S, Prensier G, Arbeille B, Ghigo JM (2004). "Global impact of mature biofilm lifestyle on Escherichia coli K-12 gene expression." Mol Microbiol 51(3);659-74. PMID: 14731270
Campbell03: Campbell JW, Morgan-Kiss RM, E Cronan J (2003). "A new Escherichia coli metabolic competency: growth on fatty acids by a novel anaerobic beta-oxidation pathway." Mol Microbiol 47(3);793-805. PMID: 12535077
Colby92: Colby GD, Chen JS (1992). "Purification and properties of 3-hydroxybutyryl-coenzyme A dehydrogenase from Clostridium beijerinckii ("Clostridium butylicum") NRRL B593." Appl Environ Microbiol 58(10);3297-302. PMID: 1444364
Cornillot97: Cornillot E, Nair RV, Papoutsakis ET, Soucaille P (1997). "The genes for butanol and acetone formation in Clostridium acetobutylicum ATCC 824 reside on a large plasmid whose loss leads to degeneration of the strain." J Bacteriol 179(17);5442-7. PMID: 9286999
Dekishima11: Dekishima Y, Lan EI, Shen CR, Cho KM, Liao JC (2011). "Extending Carbon Chain Length of 1-Butanol Pathway for 1-Hexanol Synthesis from Glucose by Engineered Escherichia coli." J Am Chem Soc 133(30);11399-401. PMID: 21707101
DiazMejia09: Diaz-Mejia JJ, Babu M, Emili A (2009). "Computational and experimental approaches to chart the Escherichia coli cell-envelope-associated proteome and interactome." FEMS Microbiol Rev 33(1);66-97. PMID: 19054114
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