Structural basis for cyclodextrin recognition by Thermoactinomyces vulgaris cyclo/maltodextrin-binding protein.
The crystal structure of a Thermoactinomyces vulgaris cyclo/maltodextrin-binding protein (TvuCMBP) complexed with gamma-cyclodextrin has been determined. Like Escherichia coli maltodextrin-binding protein (EcoMBP) and other bacterial sugar-binding proteins, TvuCMBP consists of two domains, an N- and a C-domain, both of which are composed of a central beta-sheet surrounded by alpha-helices; the domains are joined by a hinge region containing three segments. gamma-Cyclodextrin is located at a cleft formed by the two domains. A common functional conformational change has been reported in this protein family, which involves switching from an open form to a sugar-transporter bindable form, designated a closed form. The TvuCMBP-gamma-cyclodextrin complex structurally resembles the closed form of EcoMBP, indicating that TvuCMBP complexed with gamma-cyclodextrin adopts the closed form. The fluorescence measurements also showed that the affinities of TvuCMBP for cyclodextrins were almost equal to those for maltooligosaccharides. Despite having similar folds, the sugar-binding site of the N-domain part of TvuCMBP and other bacterial sugar-binding proteins are strikingly different. In TvuCMBP, the side-chain of Leu59 protrudes from the N-domain part into the sugar-binding cleft and orients toward the central cavity of gamma-cyclodextrin, thus Leu59 appears to play the key role in binding. The cleft of the sugar-binding site of TvuCMBP is also wider than that of EcoMBP. These findings suggest that the sugar-binding site of the N-domain part and the wide cleft are critical in determining the specificity of TvuCMBP for gamma-cyclodextrin.
Tonozuka
Takashi
T
Department of Applied Biological Science, Tokyo University of Agriculture and Technology, Japan. tonozuka@cc.tuat.ac.jp
Sogawa
Akiko
A
Yamada
Mitsugu
M
Matsumoto
Naoki
N
Yoshida
Hiromi
H
Kamitori
Shigehiro
S
Ichikawa
Kazuhiro
K
Mizuno
Masahiro
M
Nishikawa
Atsushi
A
Sakano
Yoshiyuki
Y
D001426:Bacterial Proteins / Q000737:chemistry*; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry*; D005453:Fluorescence; D008848:Micromonosporaceae / Q000737:chemistry*; D011134:Polysaccharides / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D047408:gamma-Cyclodextrins / Q000378:metabolism*
D001426:Bacterial Proteins; D002352:Carrier Proteins; D011134:Polysaccharides; D047408:gamma-Cyclodextrins; C008315:maltodextrin; C023792:gamma-cyclodextrin