Biology Reference
In-Depth Information
solution with the content of tube #6 of Crystal Screen kit formulation
(30% PEG4000, pH 7.5 and 0.2 M magnesium chloride hexahydrate),
precipitation in the drop appears too heavy, the protein concentration has
to be reduced by half. If there is no immediate precipitation in drop #6 or
even drop #4 (2 M ammonium sulfate, pH 8.5), protein concentration
should be increased twofold for subsequent crystallization trials
(www.hamptonresearch.com/stuff/tips99.html). It should be emphasized
that protein concentration in this pre-crystallization test is not a variable
factor, since it is kept constant from experiment to experiment. There has
also been a report on growing crystals of R14 virus from ammonium sul-
fate at concentration
x
% saturation and
y
(mg/ml) concentration of R14
virus, but only if the product of
x
and
y
is numerically between 5-10 units
(Erickson
et al
., 1983).
Summary
The marketing tagline of Hampton Research Inc. (Laguna Hill, CA, USA)
is: “behind every structure is a crystal.” This small object (
0.1 mm) is the
most important in determining the detailed arrangement of atoms. This
knowledge is necessary for structure-based drug design, which in turn
facilitates the production of effective drugs to treat disease. Traditional
wisdom regarding crystallization indicates that there are no clearly
defined rules governing how to find (or choose) the composition of the
crystallization medium that will result in crystals suitable for the acquisi-
tion of high-resolution diffraction data. It is well known that protein and
precipitant concentrations are two parameters that are crucial for crystal-
lization. It is obvious that if two parameters are relevant to a result, their
product will very likely be relevant too; the product of these two concen-
trations is a decisive parameter to vary. This approach has not yet been
recognized or applied to crystallization. Instead, it has been recommended
that varying protein concentration and keeping precipitant concentration
constant or
vice versa
is a good way to find crystallization conditions.
The general approach of screening for crystallization conditions by
simultaneously varying protein concentration and concentration of
∼
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