Molecular characterization and expression of a cDNA encoding fructan:fructan 6G‐fructosyltransferase from asparagus (Asparagus officinalis)

Abstract

* Fructan:fructan 6G-fructosyltransferase (6G-FFT) catalyses a transfructosylation from fructooligosaccharides to C6 of the glucose residue of sucrose or fructooligosacchrides. In asparagus (Asparagus officinalis), 6G-FFT is important for the synthesis of inulin neoseries fructan. Here, we report the isolation and functional analysis of the gene encoding asparagus 6G-FFT. * A cDNA clone was isolated from asparagus cDNA library. Recombinant protein was produced by expression system of Pichia pastoris. To measure enzymatic activity, recombinant protein was incubated with sucrose, 1-kestose, 1-kestose and sucrose, or neokestose. The reaction products were detected by high performance anion-exchange chromatography. * The deduced amino acid sequence of isolated cDNA was similar to that of fructosyltransferases and vacuolar type invertases from plants. Recombinant protein mainly produced inulin neoseries fructan, such as 1F, 6G-di-beta-D-fructofuranosylsucrose and neokestose. * Recombinant protein demonstrates 6G-FFT activity, and slight fructan:fructan 1-fructosyltransferase (1-FFT) activity. The ratio of 6G-FFT activity to 1-FFT activity was calculated to be 13. The characteristics of the recombinant protein closely resemble those of the 6G-FFT from asparagus roots, except for a difference in accompanying 1-FFT activity.