title: Intrinsic Levanase Activity of Bacillus subtilis 168 Levansucrase (SacB).
abstract: Levansucrase catalyzes the synthesis of fructose polymers through the transfer of fructosyl units from sucrose to a growing fructan chain. Levanase activity of Bacillus subtilis levansucrase has been described since the very first publications dealing with the mechanism of levan synthesis. However, there is a lack of qualitative and quantitative evidence regarding the importance of the intrinsic levan hydrolysis of B. subtilis levansucrase and its role in the levan synthesis process. Particularly, little attention has been paid to the long-term hydrolysis products, including its participation in the final levan molecules distribution. Here, we explored the hydrolytic and transferase activity of the B. subtilis levansucrase (SacB) when levans produced by the same enzyme are used as substrate. We found that levan is hydrolyzed through a first order exo-type mechanism, which is limited to a conversion extent of around 30% when all polymer molecules reach a structure no longer suitable to SacB hydrolysis. To characterize the reaction, Isothermal Titration Calorimetry (ITC) was employed and the evolution of the hydrolysis products profile followed by HPLC, GPC and HPAEC-PAD. The ITC measurements revealed a second step, taking place at the end of the reaction, most probably resulting from disproportionation of accumulated fructo-oligosaccharides. As levanase, levansucrase may use levan as substrate and, through a fructosyl-enzyme complex, behave as a hydrolytic enzyme or as a transferase, as demonstrated when glucose and fructose are added as acceptors. These reactions result in a wide variety of oligosaccharides that are also suitable acceptors for fructo-oligosaccharide synthesis. Moreover, we demonstrate that SacB in the presence of levan and glucose, through blastose and sucrose synthesis, results in the same fructooligosaccharides profile as that observed in sucrose reactions. We conclude that SacB has an intrinsic levanase activity that contributes to the final levan profile in reactions with sucrose as substrate.
authors.affiliation: Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México.
authors.forename: Luz
authors.initials: L
authors.lastname: Méndez-Lorenzo
authors.affiliation: Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México.
authors.forename: Jaime R
authors.initials: JR
authors.lastname: Porras-Domínguez
authors.affiliation: Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México.
authors.forename: Enrique
authors.initials: E
authors.lastname: Raga-Carbajal
authors.affiliation: Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México.
authors.forename: Clarita
authors.initials: C
authors.lastname: Olvera
authors.affiliation: Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México.
authors.forename: Maria Elena
authors.initials: ME
authors.lastname: Rodríguez-Alegría
authors.affiliation: Laboratorio de Biofisicoquímica, Departamento de Fisicoquímica, Facultad de Química, Universidad Nacional Autónoma de México, Distrito Federal, México.
authors.forename: Ernesto
authors.initials: E
authors.lastname: Carrillo-Nava
authors.affiliation: Laboratorio de Biofisicoquímica, Departamento de Fisicoquímica, Facultad de Química, Universidad Nacional Autónoma de México, Distrito Federal, México.
authors.forename: Miguel
authors.initials: M
authors.lastname: Costas
authors.affiliation: Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México.
authors.forename: Agustín
authors.initials: A
authors.lastname: López Munguía
mesh_terms: D001412:Bacillus subtilis / Q000201:enzymology*; D002151:Calorimetry; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D005630:Fructans / Q000378:metabolism; D005632:Fructose; D005947:Glucose / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000378:metabolism*; D006602:Hexosyltransferases / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D008970:Molecular Weight
chemical_list: D005630:Fructans; D005632:Fructose; D006602:Hexosyltransferases; C021513:levansucrase; D006026:Glycoside Hydrolases; C021512:levanase; D005947:Glucose