The levansucrase and inulosucrase enzymes of XXXX 121 catalyse processive and non-processive transglycosylation reactions.

@entity44627 @entity535 @entity6374 @entity71502 @entity969 @entity413
Bacterial fructosyltransferase (FTF) enzymes synthesize fructan polymers from @entity969 . FTFs catalyse two different reactions, depending on the nature of the acceptor, resulting in: (i) transglycosylation, when the growing fructan chain (polymerization), or mono- and oligosaccharides (oligosaccharide synthesis), are used as the acceptor substrate; (ii) hydrolysis, when water is used as the acceptor. @entity6374 121 levansucrase (Lev) and inulosucrase (Inu) enzymes are closely related at the @entity535 sequence level (86 % similarity). Also, the eight @entity535 residues known to be involved in catalysis and/or @entity969 binding are completely conserved. Nevertheless, these enzymes differ markedly in their reaction and product specificities, i.e. in beta(2-->6)- versus beta(2-->1)-glycosidic-bond specificity (resulting in levan and inulin synthesis, respectively), and in the ratio of hydrolysis versus transglycosylation activities [resulting in @entity413 and fructooligosaccharides (FOSs)/polymer synthesis, respectively]. The authors report a detailed characterization of the transglycosylation reaction products synthesized by the Lb. @entity6374 121 Lev and Inu enzymes from @entity969 and related oligosaccharide substrates. Lev mainly converted @entity969 into a large levan polymer (processive reaction), whereas Inu synthesized mainly a broad range of FOSs of the inulin type (non-processive reaction). Interestingly, the two FTF enzymes were also able to utilize various inulin-type FOSs ( @entity44627 , 1,1-nystose and @entity71502 ) as substrates, catalysing a disproportionation reaction; to the best of our knowledge, this has not been reported for bacterial FTF enzymes. Based on these data, a model is proposed for the organization of the sugar-binding subsites in the two Lb. @entity6374 121 FTF enzymes. This model also explains the catalytic mechanism of the enzymes, and differences in their product specificities.
