1. Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, United States
2. Center for Molecular Modeling, Center for Information Technology, National Institutes of Health, Bethesda, Maryland 20892, United States
3. Department of Biochemistry & Molecular Biology, University of Chicago, Chicago, Illinois 60637, United States
4. Department of Bioengineering, University of Illinois at Chicago, Chicago, Illinois 60607, United States