Three-dimensional structure of cyclodextrin glycosyltransferase from Bacillus circulans at 3·4 Å resolution

• Published in: Journal of molecular biology Vol. 209; no. 4; pp. 793 - 800
• Main Authors: Hofmann, Birgit E., Bender, Hans, Schulz, George E.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.10.1989
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/0022-2836(89)90607-4

Cyclodextrin glycosyltransferase (EC 2.4.1.19) from Bacillus circulans has been purified, crystallized and analyzed by X-ray diffraction. The enzyme is monomeric. SDS/polyacrylamide gel electrophoresis gave an M r of 73,600(±1000), corresponding to 670(±10) amino acid residues. The structure of the crystalline enzyme has been elucidated at a resolution of 3·4 Å, using multiple isomorphous replacement and solvent flattening for phase determination. The resulting electron density map allowed tracing of the polypeptide chain; 664 residue positions have been assigned. The chain fold has been subdivided into five domains. The N-terminal domain forms a (βα) 8-barrel, which contains the second domain of about 55 residues as an insert after the third β-strand. The three remaining domains form almost exclusively β-pleated sheet structures and consist of about 90, 80 and 95 residues. The chain fold of the three N-terminal domains of 492 residues resembles closely the two known structures of α-amylases. This geometric similarity corresponds to the observed amino acid sequence homology. On the basis of the sequence homology with α-amylases, the active center can be located. The fourth domain has an immunoglobulin fold and is far away from the active center, while the fifth domain participates in the formation of the broad depression at the active center. Accordingly, the cyclodextrin glycosyltransferase chain fold can be considered as an α-amylase chain fold with two additional domains.