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A hair seeding technique has been developed to obtain diffraction quality
crystals of yeast (Saccharomyces cerevisiae) iso-2-cytochrome c, a model for
studies of protein folding and biological electron transfer reactions. Deep red
crystals of this protein were obtained from 88 to 92% saturated solutions of
ammonium sulfate containing 20 mg protein/ml, 0.1 M-sodium phoshate, 0.3
M-sodium chloride, 0.04 M-dithiothreitol and adjusted to phosphate, 0.3 M-sodium
chloride, 0.04 M-dithiothreitol and adjusted to pH 6.0. Rapid crystal growth was
observed, but only along the path of the seeding hair stroke. The space group is
P4(3)2(1)2 (or P4(1)2(1)2) with a = b = 36.4 A, c = 137.8 A (1 A = 0.1 nm) and Z
= 8. Crystals are stable in the X-ray beam for more than 10 days and diffract to
at least 2.5 A resolution. The same hair seeding methodology has proven useful
in obtaining crystals of specifically designed mutant iso-2 proteins and in
other protein systems where consistent crystal growth had previously proven
difficult to attain.
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