1. Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306, Department of Biochemistry & Molecular Biology, School of MedicineMail Code L224, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239-3098, and Center for Computational Sciences and the Department of Chemistry and Biochemistry, Duquesne University, 600 Forbes Avenue, Pittsburgh, Pennsylvania 15282