Institute of Structural and Molecular Biology, University College London, London, United Kingdom.|Institute of Structural and Molecular Biology, University College London, London, United Kingdom.|Institute of Structural and Molecular Biology, University College London, London, United Kingdom.|Department of Biochemical Engineering, University College London, London, United Kingdom.|Department of Biochemical Engineering, University College London, London, United Kingdom.|Institute of Structural and Molecular Biology, University College London, London, United Kingdom.