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.
|Superclasses:||Biosynthesis → Carbohydrates Biosynthesis → Polysaccharides Biosynthesis|
Some taxa known to possess this pathway include : Komagataeibacter xylinus
Expected Taxonomic Range:
Acetan is an acidic heteropolysaccharide produced by the bacterium Gluconacetobacter xylinus (previously known as Acetobacter xylinum) that consists of a cellulose backbone with side-chains attached to alternate glucose units.
The polymer is composed of repeating units of a heptasaccharide with the following structure: α-L-rhamnose-(1->6)-β-D-glucose-(1->6)-α-D-glucose-(1->4)-β-D-glucuronate-(1->2)-α-D-mannose-(1->3)-β-D-glucose-(1->4)-β-D-glucose. These repeating units are attached to each other via β(1->4) links between the terminal two glucose units, forming a cellulose backbone with alternating pentasaccharide branches [Jansson93, Colquhoun95].
The biosynthetic pathway by which acetan is produced involves several steps:
(1) assembly of heptasaccharide subunits attached to an inner-membrane polyprenol phosphate carrier
(2) addition of acetyl groups
(3) polymerization of the heptasaccharide repeating units and secretion out of the cell.
The genes that encode the enzymes of this pathway are located in a cluster, which was identified and isolated using PCR amplification of a conserved region of UDP-glycosyl transferase enzymes from other organisms [Griffin94]. The initial work identified three genes - aceA, aceC, and manB - a gene that encodes a bifunctional phosphomannose isomerase/GDP-mannose pyrophosphorylase. Further work identified several additional genes, including aceC, aceP, aceQ and aceR. Gene-disrupted mutants were prepared for almost all genes, and the activity of their products was identified [Griffin96, Griffin96a, Edwards99, Ishida02].
The final assembly of the polymer involves the translocation of the matture pentasaccharide unit from the cytoplasm to the periplasm, polymerization and export via the outer membrane. Two genes proposed to be involved in this process are aceD and aceE [Griffin96a].
Colquhoun95: Colquhoun IJ, Defernez M, Morris VJ (1995). "NMR studies of acetan and the related bacterial polysaccharide, CR1/4, produced by a mutant strain of Acetobacter xylinum." Carbohydr Res 269(2);319-31. PMID: 7780996
Edwards99: Edwards KJ, Jay AJ, Colquhoun IJ, Morris VJ, Gasson MJ, Griffin AM (1999). "Generation of a novel polysaccharide by inactivation of the aceP gene from the acetan biosynthetic pathway in Acetobacter xylinum." Microbiology 145 ( Pt 6);1499-506. PMID: 10411277
Griffin96: Griffin AM, Morris VJ, Gasson MJ (1996). "Identification, cloning and sequencing the aceA gene involved in acetan biosynthesis in Acetobacter xylinum." FEMS Microbiol Lett 137(1);115-21. PMID: 8935665
Griffin96a: Griffin AM, Morris VJ, Gasson MJ (1996). "Genetic analysis of the acetan biosynthetic pathway in Acetobacter xylinum: nucleotide sequence analysis of the aceB, aceC, aceD and aceE genes." DNA Seq 6(5);275-84. PMID: 8988363
Abdian00: Abdian PL, Lellouch AC, Gautier C, Ielpi L, Geremia RA (2000). "Identification of essential amino acids in the bacterial alpha -mannosyltransferase aceA." J Biol Chem 275(51);40568-75. PMID: 11001941
Barreras06: Barreras M, Bianchet MA, Ielpi L (2006). "Crystallization and preliminary crystallographic characterization of GumK, a membrane-associated glucuronosyltransferase from Xanthomonas campestris required for xanthan polysaccharide synthesis." Acta Crystallogr Sect F Struct Biol Cryst Commun 62(Pt 9);880-3. PMID: 16946469
Barreras08: Barreras M, Salinas SR, Abdian PL, Kampel MA, Ielpi L (2008). "Structure and mechanism of GumK, a membrane-associated glucuronosyltransferase." J Biol Chem 283(36);25027-35. PMID: 18596046
Chou97: Chou FL, Chou HC, Lin YS, Yang BY, Lin NT, Weng SF, Tseng YH (1997). "The Xanthomonas campestris gumD gene required for synthesis of xanthan gum is involved in normal pigmentation and virulence in causing black rot." Biochem Biophys Res Commun 233(1);265-9. PMID: 9144435
Geremia96: Geremia RA, Petroni EA, Ielpi L, Henrissat B (1996). "Towards a classification of glycosyltransferases based on amino acid sequence similarities: prokaryotic alpha-mannosyltransferases." Biochem J 318 ( Pt 1);133-8. PMID: 8761462
Geremia99: Geremia RA, Roux M, Ferreiro DU, Dauphin-Dubois R, Lellouch AC, Ielpi L (1999). "Expression and biochemical characterisation of recombinant AceA, a bacterial alpha-mannosyltransferase." Mol Gen Genet 261(6);933-40. PMID: 10485283
Ielpi93: Ielpi L, Couso RO, Dankert MA (1993). "Sequential assembly and polymerization of the polyprenol-linked pentasaccharide repeating unit of the xanthan polysaccharide in Xanthomonas campestris." J Bacteriol 175(9);2490-500. PMID: 7683019
Katzen98: Katzen F, Ferreiro DU, Oddo CG, Ielmini MV, Becker A, Puhler A, Ielpi L (1998). "Xanthomonas campestris pv. campestris gum mutants: effects on xanthan biosynthesis and plant virulence." J Bacteriol 180(7);1607-17. PMID: 9537354
Petroni96: Petroni EA, Ielpi L (1996). "Isolation and nucleotide sequence of the GDP-mannose:cellobiosyl-diphosphopolyprenol alpha-mannosyltransferase gene from Acetobacter xylinum." J Bacteriol 178(16);4814-21. PMID: 8759843
Rubio06: Rubio S, Larson TR, Gonzalez-Guzman M, Alejandro S, Graham IA, Serrano R, Rodriguez PL (2006). "An Arabidopsis mutant impaired in coenzyme A biosynthesis is sugar dependent for seedling establishment." Plant Physiol 140(3);830-43. PMID: 16415216
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