Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland.|Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA.|Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA.|Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA.|Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland.|Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA.