1. Institute for Cell and Molecular Biosciences, Newcastle University, The Medical School, Newcastle upon Tyne NE2 4HH, U.K.
2. York Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York YO10 5YW, U.K.
3. Department of Biochemistry, Queen's University, Kingston K7L 3N6, Ontario, Canada
4. Novozymes A/S, Brudelysvej 26, 2880 Bagsvaerd, Denmark.