Cf. Snook et Ba. Wallace, The molecular-replacement solution of an intermediate-sized helical polypeptide, antiamoebin I, ACT CRYST D, 55, 1999, pp. 1539-1545
The successful use of molecular-replacement methods for the solution of the
intermediate-sized helical polypeptide antiamoebin I required the careful
consideration of a number of parameters and exhibited some unusual characte
ristics when compared with molecular-replacement solutions of globular prot
eins. High-resolution data were required owing to several features, includi
ng the comma-like shape of the molecule (which results in a pseudo-symmetri
c structure at low resolution), the relative uniformity of the structure in
the direction along the helix axis and the small differences between the t
wo independent molecules in the P1 asymmetric unit. Other parameters which
were important for the solution of this relatively low solvent content clos
ely packed cell included the radius of integration, the use of normalized s
tructure factors and especially the choice of starting model.