Epitaxial jumps

By a combination of seeding and changing the growth medium new crystal form s may be obtained. The procedure is called an epitaxial jump. The seeds use d in the seeding are from crystals of the same or related protein. For exam ple, seeding followed by an increase in precipitant concentration has given higher diffracting crystals of the complex between tissue factor, factor V IIa and the inhibitor 5L15. For both an anti-steroid antibody fragment and human placental alkaline phosphatase a polymorph was obtained by changing a low molecular weight polyethylene glycol (PEG) with one of a higher molecu lar weight. In the first case, in one direction and in the latter case, in the other direction. A change of conformation could also have contributed t o this. A DsbA mutant illustrates how such changes, result in a different p acking from that for the wild-type. Seeding from crystals of wild-type prot ein yields crystals which appear to be morphologically different from both the wild-type and mutant crystal forms. (C) 1999 Elsevier Science B.V. All rights reserved.