Program in Molecular Structure and Function, Hospital for Sick Children, Toronto, Ontario, Canada. peregrin@ebi.ac.uk|Program in Molecular Structure and Function, Hospital for Sick Children, Toronto, Ontario, Canada. peregrin@ebi.ac.uk|Program in Molecular Structure and Function, Hospital for Sick Children, Toronto, Ontario, Canada. peregrin@ebi.ac.uk|Program in Molecular Structure and Function, Hospital for Sick Children, Toronto, Ontario, Canada. peregrin@ebi.ac.uk