Comparative biochemical analysis of full-length and truncated BaqA α-amylases from Bacillus aquimaris MKSC 6.2

Abstract

BaqA is a raw starch degrading α-amylase produced by the marine bacterium Bacillus aquimaris MKSC 6.2, associated with soft corals. This α-amylase belongs to a new subfamily Glycoside Hydrolases (GH) 13_45 which has several unique characteristics, namely, a pair of tryptophan residues Trp201 and Trp202, a distinct LPDIx signature in the Conserved Sequence Region-V (CSR-V), and an elongated C-terminus containing five aromatic residues. The research aims to investigate physicochemical, kinetics, and biochemical properties of BaqA. In this study, the full-length enzyme (BaqA) and a truncated form of BaqA (designated as BaqAΔC), lacking the C-terminal 34 amino acids were constructed and expressed in Escherichia coli ArcticExpress (DE3). BaqA formed inclusion bodies, while BaqAΔC was produced as a soluble protein. Purified and refolded BaqA exhibited a catalytic efficiency (kcat/Km) of 53.1 ± 6.3 mL mg−1 s−1 at 40 °C and pH 7.5, whereas the purified BaqAΔC displayed kcat/Km of 11.4 ± 1.3 mL mg−1 s−1 under the optimum condition of 50 °C and pH 6.5. Moreover, BaqAΔC showed a slight reduction in the binding affinity towards sago granules. Interestingly, BaqAΔC displayed robust stability and halotolerant properties compared to BaqA. BaqAΔC maintained 50 % amylolytic activity for up to 6 h, whereas BaqA lost over 50 % of its activity within 90 min. Furthermore, BaqAΔC showed a remarkable increase in amylolytic activity upon the addition of NaCl, with an optimum concentration of 0.5 M. Even at a high salt concentration (1.5 M NaCl), BaqAΔC retained over 50 % of its residual activity. Taken together, its solubility, amylolytic activity, stability, ability to degrade raw starch, and moderate halotolerance make BaqAΔC a promising candidate for various starch processing industries.

Keywords

• α-Amylase
• BaqA
• BaqΔC
• C-terminal region
• Moderately halotolerant
• Raw starch