Structure
Volume 5, Issue 8, 15 August 1997, Pages 997-1015
Journal home page for Structure

Research Article
Extensive features of tight oligosaccharide binding revealed in high-resolution structures of the maltodextrin transport/chemosensory receptor

https://doi.org/10.1016/S0969-2126(97)00253-0Get rights and content
Under an Elsevier user license
open archive

Abstract

Background: Active-transport processes perform a vital function in the life of a cell, maintaining cell homeostasis and allowing access of nutrients. Maltodextrin/maltose-binding protein (MBP; Mr = 40K) is a receptor protein which serves as an initial high-affinity binding component of the active-transport system of maltooligosaccharides in bacteria. MBP also participates in chemotaxis towards maltooligosaccharides. The interaction between MBP and specific cytoplasmic membrane proteins initiates either active transport or chemotaxis. In order to gain new understanding of the function of MBP, especially its versatility in binding different linear and cyclic oligosaccharides with similar affinities, we have undertaken high-resolution X-ray analysis of three oligosaccharide-bound structures.

Results: The structures of MBP complexed with maltose, maltotriose and maltotetraose have been refined to high resolutions (1.67 to 1.8 Å). These structures provide details at the atomic level of many features of oligosaccharide binding. The structures reveal differences between buried and surface binding sites and show the importance of hydrogen bonds and van der Waals interactions, especially those resulting from aromatic residue stacking. Insights are provided into the structural plasticity of the protein, the binding affinity and the binding specificity with respect to α/β anomeric preference and oligosaccharide length. In addition, the structures demonstrate the different conformations that can be adopted by the oligosaccharide within the complex.

Conclusions: MBP has a two-domain structure joined by a hinge-bending region which contains the substrate-binding groove. The bound maltooligosaccharides have a ribbon-like structure: the edges of the ribbon are occupied by polar hydroxyl groups and the flat surfaces are composed of nonpolar patches of the sugar ring faces. The polar groups and nonpolar patches are heavily involved in forming hydrogen bonds and van der Waals contacts, respectively, with complimentary residues in the groove. Hinge-bending between the two domains enables the participation of both domains in the binding and sequestering of the oligosaccharides. Changes in the subtle contours of the binding site allow binding of maltodextrins of varying length with similarly high affinities. The fact that the three bound structures are essentially identical ensures productive interaction with the oligomeric membrane proteins, which are distinct for transport and chemotaxis.

Keywords

active transport
chemotaxis
maltodextrin-binding protein structure
oligosaccharide conformation
protein–oligosaccharide interactions

Cited by (0)

FA Quiocho (corresponding author), Howard Hughes Medical Institute, Baylor College of Medicine, Department of Biochemistry, Houston, TX 77030, USA; e-mail: [email protected].

JC Spurlino, Howard Hughes Medical Institute, Baylor College of Medicine, Houston, TX 77030, USA.

Present address for JC Spurlino: 3-Dimensional Pharmaceuticals, Inc. 665 Stockton Dr., Exton, PA 19341, USA.

LE Rodseth, Department of Biochemistry and Cell Biology, Rice University, Houston, TX 77021, USA.