Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, PA 15260, USA and Department of Biochemistry and Molecular Biophysics, University of Pennsylvania, Philadelphia, PA 19104, USA Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, PA 15260, USA and Department of Biochemistry and Molecular Biophysics, University of Pennsylvania, Philadelphia, PA 19104, USA.|Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, PA 15260, USA and Department of Biochemistry and Molecular Biophysics, University of Pennsylvania, Philadelphia, PA 19104, USA.