1. Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
2. Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
3. Department of Biochemistry, University of Toronto, Toronto, Ontario M5S IA8, Canada
4. Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5S IA8, Canada