Open AccessGoing soft and SAD with manganese
Author(s) -
Salgado Paula S.,
Walsh Martin A.,
Laurila Minni R. L.,
Stuart David I.,
Grimes Jonathan M.
Publication year - 2005
Publication title -
acta crystallographica section d
Language(s) - English
Resource type - Journals
ISSN - 1399-0047
DOI - 10.1107/s0907444904026800
Subject(s) - phaser , manganese , synchrotron , crystallography , atom (system on chip) , diffraction , molecule , chemistry , physics , molecular physics , materials science , computer science , optics , quantum mechanics , organic chemistry , embedded system
SAD phasing has been revisited recently, with experiments being carried out using previously unconventional sources of anomalous signal, particularly lighter atoms and softer X‐rays. A case study is reported using the 75 kDa RNA‐dependent RNA polymerase of the bacteriophase ϕ6, which binds a Mn atom and crystallizes with three molecules in the asymmetric unit. X‐ray diffraction data were collected at a wavelength of 1.89 Å and although the calculated anomalous signal from the three Mn atoms was only 1.2%, SHELXD and SOLVE were able to locate these atoms. SOLVE / RESOLVE used this information to obtain SAD phases and automatically build a model for the core region of the protein, which possessed the characteristic features of the right‐hand polymerase motif. These results demonstrate that with modern synchrotron beamlines and software, manganese phasing is a practical tool for solving the structure of large proteins.