1. Department of Biology, University of Padova, via Loredan 10, I-35131 Padova, Italy.
2. †Department of Physical Chemistry, University of Padova, via Loredan 6, I-35131 Padova, Italy.
3. Institute of Biochemistry, University of Zurich, Wintherturerstrasse 190, CH-8057 Zurich, Switzerland.