title: Routine phasing of coiled-coil protein crystal structures with AMPLE.
abstract: Coiled-coil protein folds are among the most abundant in nature. These folds consist of long wound α-helices and are architecturally simple, but paradoxically their crystallographic structures are notoriously difficult to solve with molecular-replacement techniques. The program AMPLE can solve crystal structures by molecular replacement using ab initio search models in the absence of an existent homologous protein structure. AMPLE has been benchmarked on a large and diverse test set of coiled-coil crystal structures and has been found to solve 80% of all cases. Successes included structures with chain lengths of up to 253 residues and resolutions down to 2.9 Å, considerably extending the limits on size and resolution that are typically tractable by ab initio methodologies. The structures of two macromolecular complexes, one including DNA, were also successfully solved using their coiled-coil components. It is demonstrated that both the ab initio modelling and the use of ensemble search models contribute to the success of AMPLE by comparison with phasing attempts using single structures or ideal polyalanine helices. These successes suggest that molecular replacement with AMPLE should be the method of choice for the crystallo-graphic elucidation of a coiled-coil structure. Furthermore, AMPLE may be able to exploit the presence of a coiled coil in a complex to provide a convenient route for phasing.
authors: Institute of Integrative Biology, University of Liverpool , Liverpool L69 7ZB, England.
authors: Jens M H
authors: JM
authors: Thomas
authors: Research Complex at Harwell, STFC Rutherford Appleton Laboratory , Didcot OX11 0FA, England.
authors: Ronan M
authors: RM
authors: Keegan
authors: Institute of Integrative Biology, University of Liverpool , Liverpool L69 7ZB, England.
authors: Jaclyn
authors: J
authors: Bibby
authors: Science and Technology Facilities Council, Daresbury Laboratory , Warrington WA4 4AD, England.
authors: Martyn D
authors: MD
authors: Winn
authors: Institute of Integrative Biology, University of Liverpool , Liverpool L69 7ZB, England.
authors: Olga
authors: O
authors: Mayans
authors: Institute of Integrative Biology, University of Liverpool , Liverpool L69 7ZB, England.
authors: Daniel J
authors: DJ
authors: Rigden
keywords: ab initio modelling; coiled-coil proteins; macromolecular complexes; molecular replacement; search-model ensembles