[1] Univ Cambridge, Dept Biochem, Cambridge CB2 1QW, England
[2] Royal Prince Alfred Hosp, Inst Clin Neurosci, Dept Neurosurg, Sydney, NSW, Australia
[3] Univ Sydney, Sch Mol & Microbial Biosci, Sydney, NSW, Australia
[4] Univ London Imperial Coll Sci Technol & Med, Dept Biol Chem, London, England
[5] Univ Sydney, Dept Surg, Sydney, NSW, Australia