protein structure determination using single isomorphous replacement (SIR) or single
wavelength anomalous diffraction (SAD) data is important when it is difficult
to prepare multiple isomorphous derivatives and to collect multiwavelength
anomalous diffraction (MAD) data. However the phase ambiguity intrinsic in
SIR/SAD data obstructs the use of them. The combination of direct methods
with SIR or SAD technique may solve the problem and simplify the
process of structure determination.
MAD and MIR are two major methods of de novo
solution of protein structures. The incorporation of direct methods with MAD or MIR phasing
may lead to better results.
Direct methods are also useful in
the dual-space fragment extension with or without SAD/SIR information.