Institute of Structural and Molecular Biology, UCL, Darwin Building, Gower Street, WC1E 6BT, UK.|Institute of Structural and Molecular Biology, UCL, Darwin Building, Gower Street, WC1E 6BT, UK.|Institute of Structural and Molecular Biology, UCL, Darwin Building, Gower Street, WC1E 6BT, UK.|Institute of Structural and Molecular Biology, UCL, Darwin Building, Gower Street, WC1E 6BT, UK.|Institute of Structural and Molecular Biology, UCL, Darwin Building, Gower Street, WC1E 6BT, UK.|Institute of Structural and Molecular Biology, UCL, Darwin Building, Gower Street, WC1E 6BT, UK.