All three surface tryptophans in Type IIa cellulose binding domains play a pivotal role in binding both soluble and insoluble ligands

• Published in: FEBS letters Vol. 429; no. 3; pp. 312 - 316
• Main Authors: Nagy, Tibor, Simpson, Peter, Williamson, Michael P., Hazlewood, Geoffrey P., Gilbert, Harry J., Orosz, Laszlo
• Format: Journal Article
• Language: English
• Published: England Elsevier B.V 16-06-1998
• Subjects: Bacterial Proteins - metabolism; Binding Sites; Cellulose - metabolism; Cellulose binding domain; Endo-1,4-beta Xylanases; Ligands; Mutagenesis; Nuclear Magnetic Resonance, Biomolecular; Oligosaccharides - metabolism; Protein Binding; Pseudomonas fluorescens; Pseudomonas fluorescens - enzymology; Solubility; Surface Properties; Tryptophan; Tryptophan mutant; Xylanase A; Xylosidases - metabolism; Tryptophan mutant; Xylanase A; Pseudomonas fluorescens; Cellulose binding domain
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/S0014-5793(98)00625-5

The three surface tryptophans of the Type IIa cellulose binding domain of
Pseudomonas fluorescens subsp.
cellulosa xylanase A (CBD
XYLA) were independently mutated to alanine, to create the mutants W13A, W49A and W66A. The three mutant proteins were purified, and their capacity to bind to a variety of ligands was determined. The mutant proteins have native-like structures but exhibited much weaker affinity for crystalline and amorphous cellulose and for cellohexaose than the wild type. These data indicate that all three tryptophans are important for binding to cellulose, and support a model in which the three tryptophans form an aromatic strip on the surface of the protein that binds to a single cellulose.