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FEBS Lett. 2005 Feb 14;579(5):1124-8.

Mutational analysis of the role of calcium ions in the Lactobacillus reuteri strain 121 fructosyltransferase (levansucrase and inulosucrase) enzymes.

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Centre for Carbohydrate Bioengineering, TNO-University of Groningen, PO Box 14, 9750 AA Haren, The Netherlands.


Bacterial fructosyltransferase enzymes belonging to glycoside hydrolase family 68 (GH68) are not known to require a metal cofactor. Here, we show that Ca2+ ions play an important structural role in the Lactobacillus reuteri 121 levansucrase (Lev) and inulosucrase (Inu) enzymes. Analysis of the Bacillus subtilis Lev 3D structure [Meng, G. and Futterer, K. (2003) Nat. Struct. Biol. 10, 935-941] has provided evidence for the presence of a bound metal ion, most likely Ca2+. Characterization of site-directed mutants in the putative Ca2+ ion-binding sites of Lb. reuteri Lev and Inu revealed that the Inu Asp520 and Lev Asp500 residues play an important role in Ca2+ binding. Sequence alignments of family GH68 proteins showed that this Ca2+ ion-binding site is (largely) present only in proteins of Gram-positive origin.

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