VII AUSE Congress and II ALBA User's Meeting - 2015

Phasing your XALOC data with ARCIMBOLDO

18 Jun 2015, 10:20

20m

Maxwell auditorium (ALBA Synchrotron)

Oral presentations II ALBA User's Meeting Session 6 - II ALBA User's Meeting 2015

Speaker

Rafael Junqueira Borges (IBMB-CSIC, UNESP)

Description

Phasing your XALOC data with ARCIMBOLDO Macromolecular Ab Initio phasing, from the native intensities alone with no experimental phase information or previous particular structural knowledge has been the object of a long quest, limited by two main barriers: structure size and data resolution. Beyond the first atomic resolution successes, current approaches have been developed, exploiting alternative constraints to atomicity, through use of the Patterson function, density modification and data extrapolation [1]. Our own approach relies on the combination of locating model fragments with the program PHASER [2] and density modification with the program SHELXE [3]. Appropriate search models are polyalanine alpha-helices[4], small polypeptide folds[5], DNA-binding motifs[6] or fragments from distant homologs[7]. Given the difficulties in discriminating correctly positioned fragments, many putative hypotheses have to be tested in parallel, thus calculations are performed on a grid or supercomputer. The method has been called after the Italian painter Arcimboldo, who used to compose portraits out of fruits and vegetables. In the case of our program, most collections of fragments remain a “still-life”, but some are correct enough for density modification to reveal the protein's true portrait (http://chango.ibmb.csic.es/ARCIMBOLDO). Using these methods, a number of unknown macromolecules with a few thousand atoms and resolutions around 2 Å have been solved. Performance of the single-workstation implementation ARCIMBOLDO_LITE available at XALOC will be presented.

References

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