1. Contribution from the Structural Biology/Bioinformatics, University of Bayreuth, Universitätsstr. 30, BGI, 95447 Bayreuth, Germany, and Département Pharmacochimie de la Communication Cellulaire - UMR 7175 - LC1, Université Louis Pasteur, 74, route du Rhin, F-67401 Illkirch Cedex, France