Rational design to change product specificities and thermostability of cyclodextrin glycosyltransferase from Paenibacillus sp.

Abstract

Functional modification of cyclodextrin glycosyltransferase (CGTases) for better product specificity and thermostability is of great importance for industrial applications. In the present study, we aimed to improve enzymatic product specificity and thermostability by rational design using β-CGTase from Paenibacillus sp. (pCGTase) as a model enzyme. pCGTase showed optimal activity in sodium phosphate buffer (pH 7.0) at 60 °C and retained >80% residual activity at pH 6–8 and 40 °C for 30 min. The biochemical data demonstrated that Y100I/T, S145G/P, Y167H, and A315H/R/S mutants increased starch conversion activity, particularly the β-cyclodextrin-forming activity. The structural analysis elucidated that new hydrophobic interactions might be formed with substrates. Furthermore, the substitution of tyrosine with isoleucine/histidine strengthens the hydrophobic reaction. The Ala315 was located in the calcium-binding site, and mutations on Ala315, which is surrounded by a patch of polar residues, appear to increase electrostatic interactions with peripheral residues. Therefore, Ala315 mutants were designed to improve thermostability, and A315D mutant exhibited the highest thermostability at 60–70 °C for 30 min. This study provides an effective approach for improving the product specificity and thermostability of CGTases.