Structural basis for cyclodextrin recognition by Thermoactinomyces vulgaris cyclo/maltodextrin-binding protein

Area of Science:

• Structural biology
• Biochemistry
• Microbiology

Background:

• Bacterial sugar-binding proteins, like maltodextrin-binding protein (MBP), are crucial for nutrient uptake.
• These proteins undergo conformational changes between open and closed forms to bind and transport sugars.
• Thermoactinomyces vulgaris cyclo/maltodextrin-binding protein (TvuCMBP) is a bacterial protein with potential roles in carbohydrate metabolism.

Purpose of the Study:

• To determine the crystal structure of TvuCMBP complexed with gamma-cyclodextrin.
• To elucidate the structural basis for TvuCMBP's interaction with cyclodextrins.
• To compare the structural features of TvuCMBP with other bacterial sugar-binding proteins.

Main Methods:

• X-ray crystallography to determine the 3D structure of the TvuCMBP-gamma-cyclodextrin complex.
• Fluorescence spectroscopy to assess binding affinities for cyclodextrins and maltooligosaccharides.

Main Results:

• The crystal structure reveals TvuCMBP forms a complex with gamma-cyclodextrin, adopting a closed conformation similar to Escherichia coli MBP.
• Fluorescence data indicate TvuCMBP exhibits comparable affinities for cyclodextrins and maltooligosaccharides.
• Structural analysis highlights significant differences in the sugar-binding site of TvuCMBP's N-domain, particularly the protruding Leu59 and a wider cleft, suggesting a key role in gamma-cyclodextrin specificity.

Conclusions:

• TvuCMBP complexed with gamma-cyclodextrin adopts a closed form, indicative of its functional state for sugar transport.
• The unique structural features of TvuCMBP's N-domain sugar-binding site, including Leu59 and a wider cleft, are critical for its specific binding of gamma-cyclodextrin.