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Solving the phase problem for carbohydrate-binding proteins using selenium derivatives of their ligands: a case study
Lieven Buts1, Remy Loris, Erwin De Genst
1Department of Ultrastructure, Vrije Universiteit Brussel, Vlaams Interuniversitair Instituut voor Biotechnologie (VIB), Pleinlaan 2, 1050 Brussels, Belgium.
Abstract:
The Escherichia coli adhesin F17-G is a carbohydrate-binding protein that allows the bacterium to attach to the intestinal epithelium of young ruminants. The structure of the 17 kDa lectin domain of F17-G was determined using the anomalous dispersion signal of a selenium-containing analogue of the monosaccharide ligand N-acetyl-d-glucosamine in which the anomeric oxygen was replaced by an Se atom. A three-wavelength MAD data set yielded good experimental phases to 2.6 A resolution. The structure was refined to 1.75 A resolution and was used to solve the structures of the ligand-free protein and the F17-G-N-acetyl-d-glucosamine complex. This selenium-carbohydrate phasing method could be of general use for determining the structures of carbohydrate-binding proteins.