1. Fraunhofer IAIS, Schloss Birlinghoven, D-53754 Sankt Augustin, Germany, Department of Life Science Informatics, B-IT, LIMES Program Unit Chemical Biology and Medicinal Chemistry, Rheinische Friedrich-Wilhelms-Universität, Dahlmannstr. 2, D-53113 Bonn, Germany, and Institute of Computer Science III, Rheinische Friedrich-Wilhelms-Universität, Römerstr. 164, D-53117 Bonn, Germany