slowly by vapor exchange with a large
reservoir solution that is initially poised
at a higher salt concentration. Since the
container is a closed system, the protein
drop will concentrate slowly with time and
hopefully produce crystals once the protein concentration exceeds the solubility.
Protein precipitate has no particular
shape but protein crystals have welldefined facets and edges despite their
large solvent content (Figure 15.9). The
overall morphology of the crystal will
usually reflect the space group of the
crystal. Proteins will often crystallize in
more than one space group as the contacts that stabilize the crystal involve
hydrogen bonds, and salt bridges can
be formed by different combinations of
surface resides.
Some proteins are crystallized easily
whereas others require much effort because the proper conditions, such as pH,
temperature, salt concentration, and protein concentration, can be found only by
trial and error, which requires considerable time, effort, and protein. Sometimes
the crystallization is restricted by limitations in the stability of a protein. All of
these problems are tremendously multiplied in proteomics, which has the goal
of determining the structure of every
protein in a given organism. Despite
these difficulties, efforts are underway in
a number of laboratories to achieve this
goal by developing expression systems
that can yield large quantities of each
gene product and large-scale robotic
control of crystallization.
DIFFRACTION FROM CRYSTALS
The diffraction pattern from a complex molecule cannot be solved directly
from Bragg’s law, but requires a more
CHAPTER 15
X-RAY DIFFRACTION AND EXAFS
323
Salt reservoir
Protein drop
Several days
Several days
Figure 15.8 Crystallization using batch- and
vapor-diffusion methods. The protein drop in the
vapor-diffusion method is usually very small, at
about 1 μl, to minimize the amount of protein.
Figure 15.9 Crystals of the protein phenoxazinone
synthase. See Smith et al. (2004).
9781405124362_4_015.qxd 4/29/08 9:13 Page 323
reservoir solution that is initially poised
at a higher salt concentration. Since the
container is a closed system, the protein
drop will concentrate slowly with time and
hopefully produce crystals once the protein concentration exceeds the solubility.
Protein precipitate has no particular
shape but protein crystals have welldefined facets and edges despite their
large solvent content (Figure 15.9). The
overall morphology of the crystal will
usually reflect the space group of the
crystal. Proteins will often crystallize in
more than one space group as the contacts that stabilize the crystal involve
hydrogen bonds, and salt bridges can
be formed by different combinations of
surface resides.
Some proteins are crystallized easily
whereas others require much effort because the proper conditions, such as pH,
temperature, salt concentration, and protein concentration, can be found only by
trial and error, which requires considerable time, effort, and protein. Sometimes
the crystallization is restricted by limitations in the stability of a protein. All of
these problems are tremendously multiplied in proteomics, which has the goal
of determining the structure of every
protein in a given organism. Despite
these difficulties, efforts are underway in
a number of laboratories to achieve this
goal by developing expression systems
that can yield large quantities of each
gene product and large-scale robotic
control of crystallization.
DIFFRACTION FROM CRYSTALS
The diffraction pattern from a complex molecule cannot be solved directly
from Bragg’s law, but requires a more
CHAPTER 15
X-RAY DIFFRACTION AND EXAFS
323
Salt reservoir
Protein drop
Several days
Several days
Figure 15.8 Crystallization using batch- and
vapor-diffusion methods. The protein drop in the
vapor-diffusion method is usually very small, at
about 1 μl, to minimize the amount of protein.
Figure 15.9 Crystals of the protein phenoxazinone
synthase. See Smith et al. (2004).
9781405124362_4_015.qxd 4/29/08 9:13 Page 323