Expression and characterization of a raw-starch glucoamylase from Aspergillus fumigatus

The raw-starch glucoamylase (RSGA) digested starch at temperatures lower than the gelatinization point, resulting in lower operational costs. In this study, a RSGA from Aspergillus fumigatus A1163 was characterized after being expressed in Escherichia coli BL21(DE3) and Pichia pastoris (currently known as Komagataella phaffii) GS115, respectively. The extracellular enzyme activity of P. pastoris (pRSGA) was 20 times that of E. coli (eRSGA). The optimal temperatures of pRSGA and eRSGA were 70 °C and 60 °C, respectively. Furthermore, the half-life of pRSGA at 60 °C reached 97 min, which is 78 min longer than that of eRSGA. EndoH reaction and mutation analysis show that glycosylation at N422 is responsible for the differences in catalytic properties between the two recombinant enzymes. pRSGA converted 92.2 % of raw corn starch (200 g/L) into glucose after 36 h at 40 °C in the presence of α-amylase and pullulanase. Our findings show that an efficient RSGA and its producing strain can be used to degrade raw starch.