Page 82 - Macromolecular Crystallography

FIRST ANALYSIS OF MACROMOLECULAR CRYS TALS 71

Table 4.4 The 65 space groups that are possible for macromolecular crystals

Crystal system Diffraction symmetry a Space groups b
Triclinic ¯ 1 P1
Monoclinic 2/m P2, P2 1 ,C2
Orthorhombic mmm P222, P222 1 ,P2 1 2 1 2, P2 1 2 1 2 1 , C222, C222 1 , F222, [I222,
I2 1 2 1 2 1 ]
Tetragonal 4/m P4, (P4 1 ,P4 3 ),P4 2 , I4, I4 1
4/mmm P422, (P4 1 22, P4 3 22), P4 2 22, P42 1 2, (P4 1 2 1 2, P4 3 2 1 2),
P4 2 2 1 2, I422, I4 1 22
Trigonal ¯ 3 P3, (P3 1 ,P3 2 ),R3
¯ 3m [P321, P312], [(P3 1 21, P3 2 21), (P3 1 12, P3 2 12)], R32
Hexagonal 6/m P6, (P6 1 ,P6 5 ), (P6 2 ,P6 4 ),P6 3
6/mmm P622, (P6 1 22, P6 5 22), (P6 2 22, P6 4 22), P6 3 22
Cubic m3 P23, P2 1 3, F23, [I23, I2 1 3]
m3m P432, (P4 1 32, P4 3 32), P4 2 32, F432, F4 1 32, I432, I4 1 32
a The overbar indicates an inversion axis, while m represents an mirror plane.
b Space groups in brackets and parentheses are indistinguishable from diffraction patterns. Those in parentheses are enantiomorphs.

Pflugrath (Pflugrath, 1997, 1999), which is marketed which are hexagonal and tetragonal are easily recog-
with MSC X-ray detectors (this program evolved nizable from their external morphology and cubic
from MADNESS) and XDS written by Wolfgang crystals may be identified from their lack of polar-
Kabsch and incorporating the IDXREF autoindex- ization. Other rectangular habits turn out often to
ing algorithm (Kabsch, 1988a, 1988b, 1993a, 1993b), be either monoclinic or orthorhombic. Coming at
which starts by calculating vectors between reflec- an indexing problem armed with this morphological
tions with low indices and building up to full information is very helpful.
data indexing. Otwinowski and Minor have writ- 2. Collect a wedge of data (say 10 frames) and also
ten the commercial, macromolecular autoindexing collect a frame at 45 and 90 away from the start-
◦
◦
routines within the PROTEUM which supports data ing oscillation position (for a crystal say whose habit
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collection of Bruker detectors. appears to have faces at 90 to each other and whose
ELVEShasbeendevelopedasanexpertsystem, by space group could be monoclinic, orthorhombic, or
James Holton and Tom Alber, to go from data collec- cubic). Collecting frames away from the starting
tion frames to structure without human intervention oscillation position can save considerable time col-
and will obviate the need for intermediate space- lecting worthless data if these frames are found to
group determination described above. Very recently, be have pathologies such as very high mosaicity
12 different European sites have been collaborat- or splitting as they will be probably encountered
ing to develop a software package known as DNA later in a full data collection when the full oscillation
(automateD collectioN of datA) for the automatic range is swung through.
collection and indexing of macromolecular diffrac- 3. Make sure you have an accurate values for the
tion data. Further information is available at the web direct-beam position on the detector you are using
site www.dna.ac.uk. and the crystal-film distance. If these have been
recorded from a previous successful data collection
and processing, time can be saved by having them
4.7.1 Starting out – preliminary data
collection and indexing as starting parameters for indexing. At many syn-
chrotrons, the prerecording of a wax ring will give
1. Look at the crystals carefully under a dissecting an accurate crystal to detector distance, sometimes
microscope equipped with polarizers. Often crystals the values displayed on the LED may be fallible.