National Magnetic Resonance Facility at Madison and Biochemistry Department, University of Wisconsin-Madison, Madison, WI 53706, USA. whlee@nmrfam.wisc.edu|National Magnetic Resonance Facility at Madison and Biochemistry Department, University of Wisconsin-Madison, Madison, WI 53706, USA. whlee@nmrfam.wisc.edu|National Magnetic Resonance Facility at Madison and Biochemistry Department, University of Wisconsin-Madison, Madison, WI 53706, USA. whlee@nmrfam.wisc.edu|National Magnetic Resonance Facility at Madison and Biochemistry Department, University of Wisconsin-Madison, Madison, WI 53706, USA. whlee@nmrfam.wisc.edu|National Magnetic Resonance Facility at Madison and Biochemistry Department, University of Wisconsin-Madison, Madison, WI 53706, USA. whlee@nmrfam.wisc.edu