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Identification and Functional Characterization of a Fructooligosaccharides-Forming Enzyme from Aspergillus aculeatus

Virgen-Ortíz, José Juan, Ibarra-Junquera, Vrani, Escalante-Minakata, Pilar, Centeno-Leija, Sara, Serrano-Posada, Hugo, de Jesús Ornelas-Paz, José, Pérez-Martínez, Jaime David, Osuna-Castro, Juan Alberto
Applied biochemistry and biotechnology 2016 v.179 no.3 pp. 497-513
Aspergillus aculeatus, amino acid sequences, genome, glycosides, glycosylation, heat treatment, kestose, models, nystose, pH, prebiotics
Although fructosyltransferases from Aspergillus aculeatus have received a considerable interest for the prebiotics industry, their amino acid sequences and structural features remain unknown. This study sequenced and characterized a fructosyltransferase from A. aculeatus (AcFT) isolated by heat treatment of Pectinex Ultra SP-L. The AcFT enzyme showed two isoforms, low-glycosylated AcFT1 and high-glycosylated AcFT2 forms, with similar optimum activity at 60 °C. The purified heat-resistant AcFT1 and AcFT2 isoforms produced identical patterns of fructooligosaccharides (FOS; kestose, nystose and fructosylnystose) with a notable transfructosylation capability (~90 % transferase/hydrolase ratio). In contrast, the pI and optimum pH values exhibited discrete differences, attributable to their glycosylation pattern. Partial protein sequencing showed that AcFT enzyme corresponds to Aspac1_37092, a putative 654-residue fructosyltransferase encoded in the genome of A. aculeatus ATCC16872. A homology model of AcFT also revealed the typical fold common to members of the glycoside hydrolase family 32 (GH32), with an N-terminal five-blade β-propeller domain enclosing catalytic residues D60, D191, and E292, linked to a C-terminal β-sandwich domain. To our knowledge, this is the first report describing the amino acid sequence and structural features of a heat-resistant FOS-forming enzyme from A. aculeatus, providing insights into its potential applications in the prebiotics industry.