Department of Bioinformatics, Boston University, Boston, MA, USA. kcrandall@gwu.edu.|Department of Bioinformatics, Boston University, Boston, MA, USA. kcrandall@gwu.edu.|Department of Bioinformatics, Boston University, Boston, MA, USA. kcrandall@gwu.edu.|Department of Bioinformatics, Boston University, Boston, MA, USA. kcrandall@gwu.edu.|Department of Bioinformatics, Boston University, Boston, MA, USA. kcrandall@gwu.edu.|Department of Bioinformatics, Boston University, Boston, MA, USA. kcrandall@gwu.edu.|Max Planck Institute of Biochemistry, Am Klopferspitz 18, Martinsried 82152, Germany. habermann@biochem.mpg.de.