title: Comparison of helical scan and standard rotation methods in single-crystal X-ray data collection strategies.
abstract: X-ray radiation in macromolecular crystallography can chemically alter the biological material and deteriorate the integrity of the crystal lattice with concomitant loss of resolution. Typical alterations include decarboxylation of glutamic and aspartic residues, breaking of disulfide bonds and the reduction of metal centres. Helical scans add a small translation to the crystal in the rotation method, so that for every image the crystal is shifted to expose a fresh part. On beamline PROXIMA 2A at Synchrotron SOLEIL, this procedure has been tested with various parameters in an attempt to understand how to mitigate the effects of radiation damage. Here, the strategies used and the crystallographic metrics for various scenarios are reported. Among these, the loss of bromine from bromophenyl moieties appears to be a useful monitor of radiation damage as the carbon-bromine bond is very sensitive to X-ray irradiation. Two cases are focused on where helical scans are shown to be superior in obtaining meaningful data compared with conventional methods. In one case the initial resolution of the crystal is extended over time, and in the second case the anomalous signal is preserved to provide greater effective multiplicity and easier phasing.
authors.affiliation: Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette, France.
authors.forename: Ivan
authors.initials: I
authors.lastname: Polsinelli
authors.affiliation: Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette, France.
authors.forename: Martin
authors.initials: M
authors.lastname: Savko
authors.affiliation: CEA, iBiTec-S, Service d'Ingénierie Moléculaire des Protéines (SIMOPRO), F-91191 Gif-sur-Yvette, France.
authors.forename: Cecile
authors.initials: C
authors.lastname: Rouanet-Mehouas
authors.affiliation: Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette, France.
authors.forename: Lidia
authors.initials: L
authors.lastname: Ciccone
authors.affiliation: Dipartimento di Farmacia, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy.
authors.forename: Susanna
authors.initials: S
authors.lastname: Nencetti
authors.affiliation: Dipartimento di Farmacia, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy.
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Orlandini
authors.affiliation: Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette, France.
authors.forename: Enrico A
authors.initials: EA
authors.lastname: Stura
authors.affiliation: Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette, France.
authors.forename: William
authors.initials: W
authors.lastname: Shepard
mesh_terms: D018360:Crystallography, X-Ray; D046911:Macromolecular Substances; D008958:Models, Molecular; D012399:Rotation; D014965:X-Rays
chemical_list: D046911:Macromolecular Substances
keywords: PROXIMA 2A; bromophenyl ligands; helical scans; micro-focus; radiation damage