[1
]Department of Biological
Sciences and Institute of Structural and Molecular Biology,
Birkbeck
College, University of London, Malet Street, London WC1E 7HX, U.K.
[2
]I07, Diamond
Light Source, Diamond House, Harwell Science &
Innovation Campus,
Didcot, Oxfordshire OX11 0DE, U.K.
[3
]Institut Laue-Langevin, 71 avenue des Martyrs - CS 20156-38042, Grenoble 38000 Cedex
9, France