1. Center for Education and Research on Macromolecules (CERM), Laboratory of Histology and Cytology, and Center for Protein Engineering (CIP), University of Liege, B6 Sart-Tilman, B-4000 Liege, Belgium, PhysIOL SA, Parc Scientifique du Sart-Tilman, Allee des noisetiers 4, B-4031 Liege, Belgium, and Service de Chimie Materiaux Nouveaux, Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium