Center for Theoretical Biological Physics, Rice University, Houston, Texas, United States of America.|Center for Theoretical Biological Physics, Rice University, Houston, Texas, United States of America.|Center for Theoretical Biological Physics, Rice University, Houston, Texas, United States of America.|Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland, United States of America.|Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland, United States of America.|Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland, United States of America.|Center for Theoretical Biological Physics, Rice University, Houston, Texas, United States of America.|Theoretical Biology and Biophysics Group, Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States of America.