Phasing the AP2 core complex with Xe, Hg and Se.

The 200 kDa core of the heterotetrameric AP2 clathrin adaptor complex was phased with xenon, mercury and selenomethionine derivatives. The phasing has been analysed in retrospect to determine how many of the derivative data sets were necessary for optimum phasing and what features were most useful in deciding which derivatives would make a positive contribution. The relative contributions of the different derivatives indicate that the most important phasing came from the two Xe data sets collected at long wavelengths (1.74 and 1.98 A) to enhance the anomalous signal. The mercury derivatives were less powerful but made a useful contribution, although inclusion of a poor second wavelength set was detrimental, probably because of radiation damage. The SeMet data were less useful for phasing because of incomplete incorporation of selenium owing to the expression conditions needed, but they were useful in chain-tracing.