title: Characterization of substrate and product specificity of the purified recombinant glycogen branching enzyme of Rhodothermus obamensis.
abstract: BACKGROUND
  Glycogen and starch branching enzymes catalyze the formation of α(1→6) linkages in storage polysaccharides by rearrangement of preexisting α-glucans. This reaction occurs through the cleavage of α(1→4) linkage and transfer in α(1→6) of the fragment in non-reducing position. These enzymes define major elements that control the structure of both glycogen and starch.
  
  
  METHODS
  The kinetic parameters of the branching enzyme of Rhodothermus obamensis (RoBE) were established after in vitro incubation with different branched or unbranched α-glucans of controlled structure.
  
  
  RESULTS
  A minimal chain length of ten glucosyl units was required for the donor substrate to be recognized by RoBE that essentially produces branches of DP 3-8. We show that RoBE preferentially creates new branches by intermolecular mechanism. Branched glucans define better substrates for the enzyme leading to the formation of hyper-branched particles of 30-70nm in diameter (dextrins). Interestingly, RoBE catalyzes an additional α-4-glucanotransferase activity not described so far for a member of the GH13 family.
  
  
  CONCLUSIONS
  RoBE is able to transfer α(1→4)-linked-glucan in C4 position (instead of C6 position for the branching activity) of a glucan to create new α(1→4) linkages yielding to the elongation of linear chains subsequently used for further branching. This result is a novel case for the thin border that exists between enzymes of the GH13 family.
  
  
  CONCLUSIONS
  This work reveals the original catalytic properties of the thermostable branching enzyme of R. obamensis. It defines new approach to produce highly branched α-glucan particles in vitro.
authors.affiliation: UGSF, UMR CNRS 8576, Université Lille 1, Villeneuve d'Ascq, France.
authors.forename: Xavier
authors.initials: X
authors.lastname: Roussel
authors.forename: Christine
authors.initials: C
authors.lastname: Lancelon-Pin
authors.forename: Anders
authors.initials: A
authors.lastname: Viksø-Nielsen
authors.forename: Agnès
authors.initials: A
authors.lastname: Rolland-Sabaté
authors.forename: Florent
authors.initials: F
authors.lastname: Grimaud
authors.forename: Gabrielle
authors.initials: G
authors.lastname: Potocki-Véronèse
authors.forename: Alain
authors.initials: A
authors.lastname: Buléon
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Putaux
authors.forename: Christophe
authors.initials: C
authors.lastname: D'Hulst
mesh_terms: D015061:1,4-alpha-Glucan Branching Enzyme / Q000737:chemistry* / Q000302:isolation & purification* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000302:isolation & purification* / Q000378:metabolism; D002384:Catalysis; D004795:Enzyme Stability; D045245:Rhodothermus / Q000201:enzymology*; D013379:Substrate Specificity / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D015061:1,4-alpha-Glucan Branching Enzyme