The invention discloses a preparation method of raw
starch-digesting glucoamylase and application of the raw
starch-digesting glucoamylase to raw
starch hydrolysis and preparation of
ethanol by simultaneous saccharification and
fermentation of raw starch. The raw starch-digesting glucoamylase is obtained after
codon optimization, and a
nucleotide sequence of the raw starch-digesting glucoamylase is shown as any of from A1) to A5): A1), sequence 3 in a sequence table; A2), nucleotides from 1st position to 1878th position in the sequence 3 in the sequence table; A3),
DNA molecules shown by nucleotides in 19th position to 1878th position in the sequence 3 in the sequence table; A4),
DNA molecules shown by nucleotides in 19th position to 1857th position in the sequence 3 in the sequence table; A5), a
protein sequence shown in sequence 4 in a coding sequence table and showing 98% identity with the sequence limited by A1), A2), A3) or A4). Through experiments, it is proven that raw starch-digesting glucoamylase genes can be effectively expressed in a
heterologous expression
system to obtain the raw starch-digesting glucoamylase rPoGA15A, and the raw starch-digesting glucoamylase rPoGA15A and alpha-
amylase act synergistically to hydrolyze the raw starch rapidly and efficiently and prepare the
ethanol by simultaneous saccharification and
fermentation of the raw starch.