Identification and characterization of novel transglycosylating α-glucosidase from Aspergillus neoniger.

Aim Aspergillus niger is well established for secreting α-glucosidase having transglycosylation activity, which is used as processing-aid for synthesis of isomaltooligosaccharides (IMO). The present study focuses on identification and characterization of a non-niger Aspergillus isolate and its gene conferring strong transglycosylation activity. Methods and results The soil isolate was identified as Aspergillus neoniger belonging to Aspergillus section Nigri using ITS (internal transcribed spacer) and β-tubulin analysis. The sequence analysis of gene responsible for α-glucosidase synthesis revealed significant nucleotide variations when compared to other Aspergillus species. Molecular docking studies using the homology model revealed the presence of threonine at 694 subsite position instead of asparagine as in case of A. niger's α-glucosidase. The enzyme was purified to several-fold using DEAE Sepharose-CL6B column and on SDS-PAGE analysis, it was found to be 145 kDa. MS/MS analysis of the purified enzyme validated the presence of threonine at 694 position. Commercial α-glucosidase (Transglucosidase L "Amano") derived from A. niger and the α-glucosidase from isolate were compared for transglycosylation activity using constant test conditions. α-glucosidase from the isolate produced 27.4% higher panose when compared to that of commercial enzyme. Moreover, the rate of secondary hydrolysis of panose is much lower in case of the isolate's enzyme. Conclusions Fungal isolate A. neoniger was characterized, and its gene conferring α-glucosidase activity was established for strong transglycosylation activity having higher panose yields. Significance To the best of our knowledge, this is the first report to establish a variant of α-glucosidase having strong transglycosylation activity from A. neoniger strain. We have demonstrated that this enzyme when used as processing-aid could improve panose significantly, which is a potential prebiotic. Also, the sequence analysis established in our studies could provide pointers for directed evolution of this enzyme to further improve transglycosylation activity.