Division of Theoretical Systems Biology, German Cancer Research Center, Heidelberg, Germany, Institute for Theoretical Biology, Charitxc3xa9-Universitxc3xa4tsmedizin, Berlin, Germany, Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California, United States of America.|Institute for Applied Mathematics, University of Heidelberg, Heidelberg, Germany.|Institute for Applied Mathematics, University of Heidelberg, Heidelberg, Germany.|Division of Theoretical Systems Biology, German Cancer Research Center, Heidelberg, Germany, Bioquant Center, University of Heidelberg, Heidelberg, Germany.