This work was done as part of the National Biomedical Computation resource project, NBCR. NBCR is supported by the National Institutes of Health (NIH) through a National Center for Research Resources program grant (P 41 RR08605) to researchers at the University of California, San Diego, including the San Diego Supercomputer Center (SDSC), the California Institute of Telecommunications and Information Technology (Cal-(IT)2), the Center for Research on Biological Structure (CRBS), The Scripps Research Institute (TSRI), and Washington University in St. Louis.