Protein Structure and Function Group, International Centre for Genetic Engineering and Biotechnology, Area Science Park, 34012 Trieste, Italy. murvai@icgeb.trieste.it|Protein Structure and Function Group, International Centre for Genetic Engineering and Biotechnology, Area Science Park, 34012 Trieste, Italy. murvai@icgeb.trieste.it|Protein Structure and Function Group, International Centre for Genetic Engineering and Biotechnology, Area Science Park, 34012 Trieste, Italy. murvai@icgeb.trieste.it