Astbury Centre for Structural Molecular Biology, Department of Biochemistry and Microbiology, University of Leeds, Leeds LS2 9JT, UK.|Astbury Centre for Structural Molecular Biology, Department of Biochemistry and Microbiology, University of Leeds, Leeds LS2 9JT, UK.|Astbury Centre for Structural Molecular Biology, Department of Biochemistry and Microbiology, University of Leeds, Leeds LS2 9JT, UK.