Department of Biological Sciences and Institute of Molecular and Structural Biology, Birkbeck, University of London, London, UK.|Department of Biological Sciences and Institute of Molecular and Structural Biology, Birkbeck, University of London, London, UK.|Department of Biological Sciences and Institute of Molecular and Structural Biology, Birkbeck, University of London, London, UK.|Department of Biological Sciences and Institute of Molecular and Structural Biology, Birkbeck, University of London, London, UK.