1. Department of Chemistry, Instrumental Analysis and Bioanalysis, Saarland University, 66123 Saarbrücken, Germany, Division for Simulation of Biological Systems, Center for Bioinformatics, Eberhard-Karls University, 72076 Tübingen, Germany, Institute of Computer Science, Algorithms in Bioinformatics, Free University of Berlin, 14195 Berlin, Germany, and European Commission, Joint Research Centre, IHCP, 21020 Ispra, Italy