- Source: Levansucrase
Levansucrase (EC 2.4.1.10) is an enzyme that catalyzes the chemical reaction
sucrose + (2,6-beta-D-fructosyl)n
⇌
{\displaystyle \rightleftharpoons }
glucose + (2,6-beta-D-fructosyl)n+1
Thus, the two substrates of this enzyme are sucrose and (2,6-beta-D-fructosyl)n, whereas its two products are glucose and (2,6-beta-D-fructosyl)n+1.
This enzyme belongs to the family of glycosyltransferases, specifically the hexosyltransferases. The systematic name of this enzyme class is sucrose:2,6-beta-D-fructan 6-beta-D-fructosyltransferase. Other names in common use include sucrose 6-fructosyltransferase, beta-2,6-fructosyltransferase, and beta-2,6-fructan:D-glucose 1-fructosyltransferase. This enzyme participates in starch and sucrose metabolism and two-component system - general.
Structural studies
As of late 2007, 3 structures have been solved for this class of enzymes, with PDB accession codes 1OYG, 1PT2, and 1W18.
References
Hehre EJ (1951). "Enzymic Synthesis of Polysaccharides: A Biological type of Polymerization". Advances in Enzymology and Related Areas of Molecular Biology. Advances in Enzymology - and Related Areas of Molecular Biology. Vol. 11. pp. 297–337. doi:10.1002/9780470122563.ch6. ISBN 978-0-470-12256-3. PMID 24540594. {{cite book}}: |journal= ignored (help)
AVIGAD G, FEINGOLD DS, HESTRIN S (1956). "The mechanism of polysaccharide production from sucrose. 3 Donor-acceptor specificity of levansucrase from Aerobacter levanicum". Biochem. J. 64 (2): 340–51. doi:10.1042/bj0640340. PMC 1199737. PMID 13363847.
Reese ET, Avigad G (1966). "Purification of levansucrase by precipitation with levan". Biochim. Biophys. Acta. 113 (1): 79–83. doi:10.1016/s0926-6593(66)80123-6. PMID 5940635.
SacB counter-selection relies on the toxic product produced by the SacB gene. sacB comes from the gram-positive bacteria Bacillus subtilis and encodes the enzyme levansucrase that converts sucrose into a toxic metabolite in gram-negative bacteria. Plating on sucrose medium will select for cells that contain constructs that have lost the sacB gene.