Characterization of a Novel Maltose-Forming α‑Amylase from Lactobacillus plantarum subsp. <i>plantarum</i> ST-III

A novel maltose (G2)-forming α-amylase from Lactobacillus plantarum subsp. <i>plantarum</i> ST-III was expressed in Escherichia coli and characterized. Analysis of conserved amino acid sequence alignments showed that L. plantarum maltose-producing α-amylase (LpMA) belongs to glycoside hydrolase family 13. The recombinant enzyme (LpMA) was a novel G2-producing α-amylase. The properties of purified LpMA were investigated following enzyme purification. LpMA exhibited optimal activity at 30 °C and pH 3.0. It produced only G2 from the hydrolysis of various substrates, including maltotriose (G3), maltopentaose (G5), maltosyl β-cyclodextrin (G2-β-CD), amylose, amylopectin, and starch. However, LpMA was unable to hydrolyze cyclodextrins. Reaction pattern analysis using 4-nitrophenyl-α-d-maltopentaoside (<i>p</i>NPG5) demonstrated that LpMA hydrolyzed <i>p</i>NPG5 from the nonreducing end, indicating that LpMA is an exotype α-amylase. Kinetic analysis revealed that LpMA had the highest catalytic efficiency (<i>k</i>_cat/<i>K</i>_m ratio) toward G2-β-CD. Compared with β-amylase, a well-known G2-producing enzyme, LpMA produced G2 more efficiently from liquefied corn starch due to its ability to hydrolyze G3