title: Crystal structure of the solute-binding protein BxlE from Streptomyces thermoviolaceus OPC-520 complexed with xylobiose.
abstract: BxlE from Streptomyces thermoviolaceus OPC-520 is a xylo-oligosaccharide (mainly xylobiose)-binding protein that serves as the initial receptor for the bacterial ABC-type xylo-oligosaccharide transport system. To determine the ligand-binding mechanism of BxlE, X-ray structures of ligand-free (open form) and ligand (xylobiose)-bound (closed form) BxlE were determined at 1.85 Å resolution. BxlE consists of two globular domains that are linked by two β-strands, with the cleft at the interface of the two domains creating the ligand-binding pocket. In the ligand-free open form, this pocket consists of a U-shaped and negatively charged groove located between the two domains. In the xylobiose-bound closed form of BxlE, both the N and C domains move to fold the ligand without conformational changes in either domain. Xylobiose is buried in the groove and wrapped by the N-domain mainly via hydrogen bond interactions and by the C-domain primarily via non-polar interactions with Trp side chains. In addition to the concave shape matching the binding of xylobiose, an inter-domain salt bridge between Asp-47 and Lys-294 limits the space in the ligand-binding site. This domain-stabilized mechanism of ligand binding to BxlE is a unique feature that is not observed with other solute-binding proteins.
authors.affiliation: Department of Physical Chemistry.
authors.forename: Koji
authors.initials: K
authors.lastname: Tomoo
authors.affiliation: Department of Physical Chemistry.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Miki
authors.affiliation: Department of Physical Chemistry.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Morioka
authors.affiliation: Department of Physical Chemistry.
authors.forename: Kiho
authors.initials: K
authors.lastname: Seike
authors.affiliation: Department of Physical Chemistry.
authors.forename: Toshimasa
authors.initials: T
authors.lastname: Ishida
authors.affiliation: Department of Microbiology, Osaka University of Pharmaceutical Sciences, Takatsuki, Osaka 569-1094, Japan.
authors.forename: Sadao
authors.initials: S
authors.lastname: Ikenishi
authors.affiliation: Department of Microbiology, Osaka University of Pharmaceutical Sciences, Takatsuki, Osaka 569-1094, Japan.
authors.forename: Katsushiro
authors.initials: K
authors.lastname: Miyamoto
authors.affiliation: Rigaku Corporation, 3-9-12 Matsubara-cho, Akishima, Tokyo 196-8666, Japan.
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Hasegawa
authors.affiliation: Rigaku Corporation, 3-9-12 Matsubara-cho, Akishima, Tokyo 196-8666, Japan.
authors.forename: Akihito
authors.initials: A
authors.lastname: Yamano
authors.affiliation: Rigaku Corporation, 3-9-12 Matsubara-cho, Akishima, Tokyo 196-8666, Japan.
authors.forename: Kensaku
authors.initials: K
authors.lastname: Hamada
authors.affiliation: Department of Microbiology, Osaka University of Pharmaceutical Sciences, Takatsuki, Osaka 569-1094, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tsujibo
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D002151:Calorimetry; D018360:Crystallography, X-Ray; D004187:Disaccharides / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D013302:Streptomyces / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D004187:Disaccharides; C004173:xylobiose
keywords: bacterial ABC transport; crystal structure; ligand-dependent conformational change; xylooligosaccharide-binding protein