title: Metabolic engineering of Agrobacterium sp. strain ATCC 31749 for production of an alpha-Gal epitope.
abstract: BACKGROUND
  Oligosaccharides containing a terminal Gal-alpha1,3-Gal moiety are collectively known as alpha-Gal epitopes. alpha-Gal epitopes are integral components of several medical treatments under development, including flu and HIV vaccines as well as cancer treatments. The difficulty associated with synthesizing the alpha-Gal epitope hinders the development and application of these treatments due to the limited availability and high cost of the alpha-Gal epitope. This work illustrates the development of a whole-cell biocatalyst for synthesizing the alpha-Gal epitope, Gal-alpha1,3-Lac.
  
  
  RESULTS
  Agrobacterium sp. ATCC 31749 was engineered to produce Gal-alpha1,3-Lac by the introduction of a UDP-galactose 4'-epimerase:alpha1,3-galactosyltransferase fusion enzyme. The engineered Agrobacterium synthesized 0.4 g/L of the alpha-Gal epitope. Additional metabolic engineering efforts addressed the factors limiting alpha-Gal epitope production, namely the availability of the two substrates, lactose and UDP-glucose. Through expression of a lactose permease, the intracellular lactose concentration increased by 60 to 110%, subsequently leading to an improvement in Gal-alpha1,3-Lac production. Knockout of the curdlan synthase gene increased UDP-glucose availability by eliminating the consumption of UDP-glucose for synthesis of the curdlan polysaccharide. With these additional engineering efforts, the final engineered strain synthesized approximately 1 g/L of Gal-alpha1,3-Lac.
  
  
  CONCLUSIONS
  The Agrobacterium biocatalyst developed in this work synthesizes gram-scale quantities of alpha-Gal epitope and does not require expensive cofactors or permeabilization, making it a useful biocatalyst for industrial production of the alpha-Gal epitope. Furthermore, the engineered Agrobacterium, with increased lactose uptake and improved UDP-glucose availability, is a promising host for the production of other medically-relevant oligosaccharides.
authors.affiliation: School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332-0100, USA.
authors.forename: Anne M
authors.initials: AM
authors.lastname: Ruffing
authors.forename: Rachel R
authors.initials: RR
authors.lastname: Chen
mesh_terms: D000939:Epitopes / Q000235:genetics / Q000378:metabolism*; D005818:Genetic Engineering; D005964:Glucosyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012231:Rhizobium / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D000939:Epitopes; D011993:Recombinant Fusion Proteins; C036655:1,3-alpha-D-glucan synthase; D005964:Glucosyltransferases