FastEP

The FastEP pipeline is an automated experimental phasing pipeline run on the output of FastDP, if an anomalous scatterer is defined, to answer the question “can I determine my heavy atom substructure”.

Pipeline description

The FastEP pipeline (Figure 1) first performs an initial analysis to decide if there is an anomalous signal present. If this is the case then SHELXC is run to generate the input files needed for substructure determination with SHELXD. These are then duplicated and modified to generate input files for: all possible (enantiomorph-unique) spacegroups and all sensible numbers of heavy atom sites. Each of these tasks are then run on the cluster using the multi-processor version of SHELXD, and the solution with the highest combined figure-of-merit taken as correct. This solution is then phased in both enantiomorphs and with solvent fractions in the range 25% – 75% in 5% steps. The solution with the highest CC is then taken as correct and converted to MTZ format for viewing in Coot, typically within three minutes (Figure 2).

Figure 1: Workflow for experimental phasing with FastEP.

Figure 2: Illustration of results of experimental phasing with FastEP.

Viewing the pipeline outputs in ISPyB

In the downstream processing window, the FastEP results are presented with a summary table of the heavy atom sites:

as well as a graph showing the map correlation coefficent and the figure of merit versus the dataset resolution:

The found heavy atoms can be seen in an UglyMol window by selecting the Map/Model viewer:

Showing:

A summary html can be found in the Logs and Files window for FastEP: