1. Computational Biochemistry Group, Interdisciplinary Center for Scientific Computing (IWR), University of Heidelberg, Im Neuenheimer Feld 368, D69120 Heidelberg, Germany
2. Department of Physiology and Biophysics, Boston University School of Medicine, 72 East Concord Street, Boston, Massachusetts 02118, USA
3. Department of Biological Sciences, University of Massachusetts Lowell, One University Avenue, Lowell, Massachusetts 01854, USA