Improved thermostability of bacillus circulans cyclodextrin glycosyltransferase by the introduction of a salt bridge

Abstract Cyclodextrin glycosyltransferase (CGTase) catalyzes the formation of cyclodextrins from starch. Among the CGTases with known three‐dimensional structure, Thermoanaerobacterium thermosulfurigenes CGTase has the highest thermostability. By replacing amino acid residues in the B‐domain of Bacillus circulans CGTase with those from T. thermosulfurigenes CGTase, we identified a B. circulans CGTase mutant (with N188D and K192R mutations), with a strongly increased activity half‐life at 60°C. Asp188 and Arg192 form a salt bridge in T. thermosulfurigenes CGTase. Structural analysis of the B. circulans CGTase mutant revealed that this salt bridge is also formed in the mutant. Thus, the activity half‐life of this enzyme can be enhanced by rational protein engineering. Proteins 2003. © 2003 Wiley‐Liss, Inc.