Processing L498 thermolysin

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This page contains instructions for reproducing the results reported in the 2014 cctbx.xfel paper<ref name="Hattne:2014">Hattne, J et al. Accurate macromolecular structures using minimal measurements from X-ray free-electron lasers. Nat. Methods In press (2014).</ref>. The data are available from the Coherent X-ray Imaging Data Bank (CXIDB ID 23; raw XTC files, 4.0 TiB), and must be downloaded to a local disk prior to starting the analysis. Furthermore, the PSDM Software Distribution must be set up, along with a test release and an empty analysis package. A MySQL database is required to merge the integrated diffraction intensities. In the interest of keeping this guide as general as possible, no particular queuing system is assumed to be available. Processing time depends strongly on the computational resources available; using 48 processors on a 64-core 1.4 GHz Opteron-based computer, the analysis takes around 24 hours. The instructions assume some familiarity with cctbx.xfel and its installation and configuration procedure.


Installing a cctbx.xfel snapshot from March 28, 2013

The thermolysin data for the cctbx.xfel paper was processed around March 28, 2013. Unfortunately, regular nightly releases are not available for that time, but a custom source-code bundle has been prepared. This bundle differs from the regular cctbx bundles in that LABELIT is included, and that the directory layout is identical to that of a developer installation. To download and unpack the bundle in the current directory:

$ wget http://adder.lbl.gov/cctbx.xfel/downloads/cctbx.xfel-20130328.tar.gz
$ tar -xpvzf cctbx.xfel-20130328.tar.gz

Next, create a build directory (called phenix-build-20130328 below, but that is an arbitrary choice), in which the sources are configured and compiled. The Python interpreter required to complete this step must be the one supplied by the PSDM Software Distribution. Once the PSDM software has been set up, this interpreter can be located using

$ find $SIT_ROOT/sw/external/python -perm /0111 -type f -wholename "*/$SIT_ARCH/*/python"

To prepare the build directory using this interpreter

$ mkdir phenix-build-20130328
$ cd phenix-build-20130328
$ python ../phenix-src-20130328/cctbx_project/libtbx/configure.py cxi_xdr_xes xfel
$ . setpaths.sh

where python is the path to the Python interpreter located using the previous find-command. Note that csh-users should run source setpaths.csh instead of . setpaths.sh. Then compile the sources:

$ make
$ make

Note that the make command may need to be run twice in order to complete the build. Once make does not produce any output from the compiler, the build is complete.

To make the cctbx.xfel analysis modules available to PSDM's pyana,

$ cd /path/to/test/release
$ sit_setup
$ cd my_ana_pkg
$ ln -fns /path/to/phenix-src-20130328/cctbx_project/xfel/cxi/cspad_ana src
$ cd ..
$ scons

where /path/to/test/release and my_ana_pkg are the path to the test release and the name of the analysis package chosen while setting up the PSDM software distribution, respectively. /path/to denotes the path to the directory containing the unpacked cctbx.xfel sources. The last step compiles the cctbx.xfel analysis modules.


Creating a dark image

To meaningfully process the thermolysin diffraction data, an average of all the images in a dark run—a run without any X-rays impinging on the detector—must be subtracted from the individual diffraction images. The configuration file below can be used to produce such an average, as well as an image of the standard deviation of all the pixels over the course of the run.

[pyana]
modules = my_ana_pkg.mod_average
num-cpu = 4

[my_ana_pkg.mod_average]
address         = CxiDs1-0|Cspad-0
calib_dir       = /path/to/phenix-src-20130328/cctbx_project/xfel/metrology/CSPad/run4/CxiDs1.0_Cspad.0
avg_basename    = Ds1-avg
avg_dirname     = r0031
stddev_basename = Ds1-stddev
stddev_dirname  = r0031

/path/to refers to the directory containing the unpacked cctbx.xfel sources. All other options with values set in italics can be modified without adversely affecting averaging. The above file will use four simultaneous processes, and write the average and standard deviation images to files whose names start with Ds1-avg and Ds1-stddev, respectively, both in a directory called r0031.

The data deposited at the CXIDB contains a dark run, r0031. To average the images in that run, save the above configuration file to disk, e.g. L498-dark.cfg, apply modifications as necessary, and execute

$ cxi.pyana -c L498-dark.cfg /path/to/xtc/files/e157-r0031-*.xtc

where /path/to/xtc/files is the path to the directory containing the raw XTC files downloaded from CXIDB. The files written to the r0031 directory will have a current date stamp appended, which can safely be removed to simplify subsequent configuration files.

$ cd r0031
$ mv Ds1-avg20140308104336073.pickle Ds1-avg.pickle
$ mv Ds1-stddev20140308104336371.pickle Ds1-stddev.pickle
$ cd ..

Note that the date stamp on the generated files above depends on the time of their creation. Further details are available on the Create a dark image page of the tutorials.


Indexing the thermolysin data

A configuration file for processing the primary lattices in the thermolysin data is shown below.

[pyana]
modules = my_ana_pkg.mod_hitfind:threshold \
          my_ana_pkg.mod_hitfind:index
num-cpu = 48

[my_ana_pkg.mod_hitfind]
address     = CxiDs1-0|Cspad-0
calib_dir   = /path/to/phenix-src-20130328/cxi_xdr_xes/cftbx/metrology/CSPad/run4/CxiDs1.0:Cspad.0
dark_path   = r0031/Ds1-avg.pickle
dark_stddev = r0031/Ds1-stddev.pickle
db_logging  = False
detz_offset = 575

[my_ana_pkg.mod_hitfind:threshold]
dispatch        = nop
distl_flags     = permissive
distl_min_peaks = 16
threshold       = 450
xtal_target     = hitfind

[my_ana_pkg.mod_hitfind:index]
dispatch             = index
integration_dirname  = integration-first-lattice
integration_basename = int-
xtal_target          = thermolysin27

The configuration file above instructs mod_hitfind to use 48 processes. It disables all image output, which reduces the amount of disk space required to perform the analysis to about 3.4 GiB. /path/to again refers to the directory containing the unpacked cctbx.xfel sources, and dark_path as well as dark_stddev may have to be changed to reflect the location of the previously generated dark images. Integration results will be written to the directory integration-first-lattice.

Due to particularities of the thermolysin measurement, processing needs to proceed in two batches. To analyze the first batch, runs 16 through 27, save the above configuration file to disk, e.g. L498-indexigrate.cfg, apply modifications as necessary, and execute

$ cxi.pyana -c L498-indexigrate.cfg /path/to/xtc/files/e157-r0016-*.xtc
$ cxi.pyana -c L498-indexigrate.cfg /path/to/xtc/files/e157-r0017-*.xtc
$ …
$ cxi.pyana -c L498-indexigrate.cfg /path/to/xtc/files/e157-r0027-*.xtc

where /path/to/xtc/files is the path to the directory containing the raw XTC files. The second batch, runs 71 through 73, was recorded using a different distance between the interaction region and the detector. Whilst the changes to the detector position are automatically handled by cctbx.xfel, the resulting difference in shadowing is not. Different areas of the detector should be ignored at the different distances, and this is accounted for by the value of the xtal_target option in the configuration file. To analyze this set of runs, edit L498-indexigrate.cfg, change thermolysin27 to thermolysin73, and

$ cxi.pyana -c L498-indexigrate.cfg /path/to/xtc/files/e157-r0071-*.xtc
$ cxi.pyana -c L498-indexigrate.cfg /path/to/xtc/files/e157-r0072-*.xtc
$ cxi.pyana -c L498-indexigrate.cfg /path/to/xtc/files/e157-r0073-*.xtc

On successful completion, the number of files in the integration-first-lattice directory corresponds to the number of successfully integrated images. Owing to variations in hardware and compiler internals, it may deviate slightly from 11,583, the number reported in the cctbx.xfel paper<ref name="Hattne:2014"/>. Further details are available on the indexing and integration page of the tutorials.


Indexing the secondary lattice

Indexing the secondary lattice is very similar to indexing the primary lattice, but requires a change to the source code. Edit /path/to/phenix-src-20130328/labelit_regression/xfel/xfel_targets.py, and uncomment (i.e. remove the leading # character) "outlier_detection.switch=True" on line 25. Then edit the configuration file, L498-indexigrate.cfg above, and change integration-first-lattice to integration-second-lattice in order not to overwrite the results of the previous analysis of the primary lattice. Before reanalyzing the first batch, ensure that xtal_target is set to thermolysin27.

$ cxi.pyana -c L498-indexigrate.cfg /path/to/xtc/files/e157-r0016-*.xtc
$ cxi.pyana -c L498-indexigrate.cfg /path/to/xtc/files/e157-r0017-*.xtc
$ …
$ cxi.pyana -c L498-indexigrate.cfg /path/to/xtc/files/e157-r0027-*.xtc

Then set xtal_target is set to thermolysin73 in the configuration file, and process the second batch.

$ cxi.pyana -c L498-indexigrate.cfg /path/to/xtc/files/e157-r0071-*.xtc
$ cxi.pyana -c L498-indexigrate.cfg /path/to/xtc/files/e157-r0072-*.xtc
$ cxi.pyana -c L498-indexigrate.cfg /path/to/xtc/files/e157-r0073-*.xtc

The number of integrated secondary lattices should be close to 2,021, the number reported in the cctbx.xfel paper<ref name="Hattne:2014"/>.

Merging all integrated images

The phil-file below defines values suitable for merging the primary and secondary lattices previously integrated.

data                         = integration-first-lattice
data                         = integration-second-lattice
d_min                        = 2.10
merge_anomalous              = True
min_corr                     = -1
model                        = 2tli.pdb
nproc                        = 16
plot_single_index_histograms = False
raw_data.sdfac_auto          = True
rescale_with_average_cell    = True
significance_filter.apply    = True
set_average_unit_cell        = True
pixel_size                   = 0.11
mysql {
    database = db_name
    passwd   = db_passwd
    runtag   = L498_thermolysin
    user     = db_user
}
output {
    n_bins = 10
    prefix = L498_thermolysin
}
scaling {
    algorithm  = mark0
    mtz_file   = 2tli.mtz
    show_plots = False
    log_cutoff = 0.0
}

integration-first-lattice and integration-second-lattice may need to be adjusted to point to the directories where the indexing and integration step left its results. db_name, db_user, and db_passwd must be substituted with the database name and access credentials to a MySQL database. Databases on hosts other than the one used to merge the thermolysin data can be accessed by additionally specifying the mysql.host and mysql.port options. The model and structure factors for the scaling reference, model and scaling.mtz_file above, are both available for download from the RCSB Protein Data Bank (PDB ID 2tli). If the PHENIX suite is installed, these are conveniently obtained at the command line using

$ phenix.fetch_pdb --mtz 2tli

To merge the thermolysin data, save the suitably modified configuration file to e.g. L498-merge.phil, and run

$ cxi.merge L498-merge.phil
$ cxi.xmerge L498-merge.phil

Merging statistics are printed on standard output. The merged MTZ-file is written to a file whose name is determined by the value of output.prefix in the configuration file (with the values shown above, the output file would be L498_thermolysin.mtz). Note that the version of merging programs from 28 March, 2013 do not not report the Rsplit statistic.

References

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