L-Arabinose-binding protein-sugar complex at 2.4 A resolution. Stereochemistry and evidence for a structural change.

The L-arabinose molecule (in the C1 pyranose chair conformation) has been fitted to the electron density corresponding to the bound sugar in the 2.4 A resolution Fourier map of the L-arabinose-binding protein. The sugar molecule is buried in the cleft between the two lobes of the bilobate protein. All sugar hydroxyls are hydrogen-bonded to side chain residues: beta-OH(1) to Lys-10 and Asp-90, OH(2) to Lys-10, OH(3) to Asn-205 and Glu-14 (possibly via a water molecule), and OH(4) to Asn-232. Lys-10, Glu-14, and Asp-90 are associated with one domain while Asn-205 and Asn-232 are lodged in the other. Protein structural change accompanying binding is indicated by the inaccessibility of the bound L-arabinose to the aqueous environment.