β-1,2-Glucans are bacterial carbohydrates that exist in cyclic or linear forms and play an important role in infections and symbioses involving Gram-negative bacteria. Although several β-1,2-glucan-associated enzymes have been characterized, little i ...
β-1,2-Glucans are bacterial carbohydrates that exist in cyclic or linear forms and play an important role in infections and symbioses involving Gram-negative bacteria. Although several β-1,2-glucan-associated enzymes have been characterized, little is known about how β-1,2-glucan and its shorter oligosaccharides (Sop n
s) are captured and imported into the bacterial cell. Here, we report the biochemical and structural characteristics of the Sop n
-binding protein (SO-BP, Lin1841) associated with the ATP-binding cassette (ABC) transporter from the Gram-positive bacterium Listeria innocua Calorimetric analysis revealed that SO-BP specifically binds to Sop n
s with a degree of polymerization of 3 or more, with K d values in the micromolar range. The crystal structures of SO-BP in an unliganded open form and in closed complexes with tri-, tetra-, and pentaoligosaccharides (Sop 3-5 ) were determined to a maximum resolution of 1.6 Å. The binding site displayed shape complementarity to Sop n
, which adopted a zigzag conformation. We noted that water-mediated hydrogen bonds and stacking interactions play a pivotal role in the recognition of Sop 3-5 by SO-BP, consistent with its binding thermodynamics. Computational free-energy calculations and a mutational analysis confirmed that interactions with the third glucose moiety of Sop n
s are significantly responsible for ligand binding. A reduction in unfavorable changes in binding entropy that were in proportion to the lengths of the Sop n
s was explained by conformational entropy changes. Phylogenetic and sequence analyses indicated that SO-BP ABC transporter homologs, glycoside hydrolases, and other related proteins are co-localized in the genomes of several bacteria. This study may improve our understanding of bacterial β-1,2-glucan metabolism and promote the discovery of unidentified β-1,2-glucan-associated proteins.
Organizational Affiliation:
the Faculty of Agriculture, Niigata University, Niigata 950-2181, Japan.,the Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.,Department of Biomaterial Sciences, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.,From the Department of Biotechnology.,Agricultural Bioinformatics Research Unit, and.,the VTT Technical Research Centre of Finland, Espoo FI-02044 VTT, Finland, and.,From the Department of Biotechnology, asfushi@mail.ecc.u-tokyo.ac.jp.
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