Page 185 - Macromolecular Crystallography

174 MACROMOLECULAR CRYS TALLOGRAPHY

exceeded 110, with at least 45 in the United States is required. This requirement and those of the cur-
alone. This number has grown more than five-fold rent efforts in structural proteomics place a premium
since 1990 (Helliwell, 1990). on highly automated evaluation of crystals, data
Rapid collection of diffraction data depends on collection, and data processing.
access to such powerful X-ray sources. This chapter
describes how high-quality, high-throughput data
collection can be achieved. We use SGX-CAT, the 12.2 Access to synchrotrons
SGX CollaborativeAccess Team beamline, located at Crystallographers have traditionally travelled to
the Advanced Photon Source of Argonne National synchrotrons for data collection. However, this
Laboratory, as an example to illustrate the con- approach is not generally compatible with high-
cepts behind the design of, and the hardware used throughput data collection. For example, signifi-
at, synchrotron beamlines. Many of these features cant time is often expended merely in transporting
are found, individually or in combination, at other technical staff to the synchrotron facility.
beamlines. Data collection at synchrotron sources Two related alternatives for ‘mail-in’ use of syn-
produces enormous quantities of data. We, there- chrotrons have arisen. Several facilities permit users
fore, also discuss the information technology infras- to send crystals to the synchrotron beamline, where
tructure and software that is necessary for effective local staff load them onto a robot that places the
data management. crystals into the X-ray beam (see Section 12.3.3).
High-throughput data collection requires seam- The user then operates the beamline remotely, dur-
less interoperation of various hardware compo- ing a specific period allocated for their experiments.
nents. In addition, user-supplied descriptions of Considerable effort has been expended by vari-
protein crystals must be directly linked with the ous synchrotron facilities to provide robust, secure
diffraction data. Such linkages can be achieved effi- internet connections between the beamline and the
ciently with computer databases. A database that end user.
tracks production of the protein samples, crystal- Even greater efficiencies can be achieved when the
lization, and diffraction from the resultant crystals entire process of data collection is delegated to the
serves as the glue that holds the entire gene-to- staff of the beamline and the automated facilities
structure process together. In this chapter, we they operate. This latter approach is used exclu-
first discuss data collection processes and hard- sively at SGX-CAT. All decisions on data collection
ware. We then illustrate how a well-constructed protocols are made by the local staff aided by facil-
database ensures information flow through the steps ity software systems. Such reliance on professional
of data acquisition. With such a database, syn- experts for data collection was anticipated nearly a
chrotron beamline measurements can be directly decade ago (Sweet, 1998).
and efficiently integrated into the process of protein
crystallographic structure determination.
Theapproachestodataacquisitionsummarizedin 12.3 Beamline hardware
this chapter apply to both the de novo determination
12.3.1 X-ray optics
of protein structures and, as is routine in drug dis-
covery, examination of protein–ligand cocrystals. Synchrotron X-ray sources include both bending
Each type of experiment benefits from the advan- magnets and insertion devices. For protein crystal-
tagesofmodernsynchrotronX-raysources. Recently lography, an undulator insertion device is preferred
in pharmaceutical development there has been an because it provides greater intensity at a specific
emphasis on discovering lead compounds through wavelength and has lower beam divergence. This
structure-guided molecular elaboration that begins latter property results in smaller X-ray reflections.
with small chemical fragments (Jhoti, 2004). Because The configuration of X-ray optical elements at the
of the large number of cocrystals to be examined SGX-CAT undulator beamline is shown in Fig. 12.1.
in this approach, often exceeding several hun- Generally, beamline components are housed in lead-
dred, rapid access to high-quality diffraction data walled enclosures or hutches. In Fig. 12.1, the first