1. Center
for Theoretical Biological Physics and Department of Chemistry, Rice University, 6100 Main Street, Houston, Texas 77005, United States
2. Maxwell
Institute for Mathematical Sciences and School of Mathematics, The University of Edinburgh, Peter Guthrie Tait Road, Edinburgh EH9 3FD, United Kingdom
3. Department
of Mathematics, Computer Science and Bioinformatics, Freie Universität Berlin, Arnimallee 6, 14195 Berlin, Germany