Comparative Analysis of the Primary Structures of Glycoside Hydrolases

Fructan-modifying enzymes are divided into fructan-producing enzymes (fructosyl transferases) and fructan hydrolyzing enzymes (invertases, inulinases, levanases). Fructosyl transferases break the glycosidic bond of sucrose and use the energy of this bond to attach the resulting fructosyl to another sucrose molecule or other acceptor, increasing the fructan chain. Invertases hydrolyze sucrose and small fructooligosaccharides. Oligo- and polyfructans are cleaved by inulinases and levanases. A difference of only three amino acid residues affects the ability of glycoside hydrolases to cleave various substrates, in particular inulin and levan, or to exhibit transfructosylating activity. In this regard, the aim of the work was to carry out a comparative analysis of the primary structures of glycoside hydrolases of various origins. The paper presents the results of a comparative analysis of the amino acid sequences of glycoside hydrolases from the NCBI database (https://www.ncbi.nlm.nih.gov/). The overlap percentage (Query cover) of the sequences and their identity (Ident) were calculated using the Blast program (https://blast.ncbi.nlm.nih.gov/Blast.cgi). It was found that the affinity of endoinulinase from Aspergillus ficuum with 6- and 1-fructan exohydrolases from Arabidopsis thaliana and Arabidopsis lyrata subsp. Lyrata was higher (89% overlap and 24% identity) than exoinulinase from Kluyveromyces marxianus (38 and 57% overlap, 29 and 26% identity, respectively). Fructan 1-exohydrolase I from Cichorium intybus was also closer in primary structure to fungal endoinulinase (90% overlap and 25% identity) than to yeast exoinulinase (51% overlap and 27% identity). From the results obtained, the following conclusion can be drawn: the mechanism of substrate hydrolysis does not in all cases determine the degree of homology of glycoside hydrolases and related enzymes. It is possible that some glycoside hydrolases, including inulinases, can act both as endo and exo-enzymes, i.e., possess both types of catalytic activity towards fructans.