Maltodextrin-dependent crystallization of cyclomaltodextrin glucanotransferase from Bacillus circulans

Crystals of cyclomaltodextrin glucanotransferase from Bacillus circulans (EC 2.4.1.19) suitable for high-resolution X-ray analysis were obtained by vapor diffusion against 60% (v/v) 2-methyl 2,4-pentanediol buffered with 100 mM-sodium Hepes, pH 7.55. The crystals have P2(1)2(1)2(1) space group symmetry, with a = 120.4 A, b = 110.9 A and c = 66.4 A, and contain one molecule of 68,000 in the asymmetric unit. Growth of single enzyme crystals was found to require the presence of either alpha-cyclodextrin, beta-cyclodextrin, gamma-cyclodextrin, or maltose in high molar excess, a requirement that could not be fulfilled by glucose, the basic building block of these compounds. Although the exact role of cyclic and linear maltodextrins in enzyme crystallization is not yet known, we have preliminary evidence that these compounds are degraded by the enzyme in the crystallization droplet.