1. Department of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200 F, 3001 Heverlee, Belgium, Institut Curie, Service Bioinformatique, 26 Rue d'Ulm, Paris Cedex 05, 75248 France, Department of Physics and Computer Methods, University of Warmia and Masuria in Olsztyn, ul. Żolnierska 14, 10-561 Olsztyn, Poland, Hasselt University, Biomedical Research Institute, Agoralaan, Building D, B-3590 Diepenbeek, Belgium