Biologia, Bratislava, 57/Suppl. 11: 93-99, 2002.

ISSN 0006-3088 (Biologia).

 

Review

Structural basis of the synthesis of large cycloamyloses by amylomaltase.

 

Norbert Straeter1*, Ingo Przylas1, Wolfram Saenger1, Yoshinobu Terada2, Kazutoshi Fujii2, Takeshi Takaha2

1 Institut fur Chemie - Kristallographie, Freie Universitaet Berlin, Takustrasse 6, 14195 Berlin, Germany; tel.: ++ 49 30 8385 3456, fax: ++ 49 30 8385 6702, e-mail: strater@chemie.fu-berlin.de

2 Biochemical Research Laboratory, Ezaki Glico Co. Ltd., 4-6-5 Utajima, Nishiyodogawa-ku, Osaka 555-8502, Japan

* corresponding author

Received: October 22, 2001 / Accepted: April 18, 2002

 

Abstract

Large cycloamyloses probably form hydrophobic channels resembling those of V-type amylose helices. Because these channels can accomodate guest molecules, these cycloamyloses may find technical applications similar to the smaller cyclodextrins. Cycloamyloses are synthesized by bacterial amylomaltases and by the related plant D-enzymes. We have analyzed the three-dimensional structures of amylomaltase from Thermus aquaticus and also of a complex of this enzyme with the maltotetraose inhibitor acarbose in order to gain insight into the structural basis of cycloamylose formation. Amylomaltase differs from a-amylase or CGTase in the absence of a C-terminal domain C and in the presence of an additional predominantly a-helical insertion between barrel strands 2 and 3. Two acarbose molecules have bound to the enzyme, one at the active site and a second molecule ~14 away from the nonreducing end of the first acarbose. The subdomains B1, B2 and B3, which are located around the rim of the C-terminal side of the barrel, and in particular the two loops around residues 460 and 250, probably influence the product specificity.

 

Key words: acarbose, a-amylase family, glucanotransferase, protein crystallography.