1. E. C. Slater Institute, Biochemistry/FS, University of Amsterdam, Plantage Muidergracht 12, NL-1018 TV Amsterdam, The Netherlands, Department of Biochemistry, George S. Wise Faculty of Life Sciences, Ramat Aviv, 69978, Tel Aviv, Israel, and Biophysics Research Division, University of Michigan, 930 North University, Ann Arbor, Michigan 48109-1055