CONTAMINANT INCLUSION INTO PROTEIN CRYSTALS ANALYZED BY ELECTROSPRAY MASS-SPECTROMETRY AND X-RAY CRYSTALLOGRAPHY

The inclusion of protein contaminants into crystals of turkey egg whit e lysozyme (TEWL) was investigated by electrospray mass spectrometry o f the dissolved crystals. The results show that significant amounts of the structurally related contaminant hen egg white lysozyme (HEWL) ar e included in the crystals of TEWL. The structurally unrelated contami nant RNAse A, on the other hand, is not included. The X-ray diffractio n data statistics of a hybrid TEWL/HEWL crystal and an uncontaminated TEWL crystal were of similar quality. This indicates that, even though the crystals contain much higher levels of the contaminant than one w ould have expected after a recrystallization experiment, they are stil l suitable for X-ray diffraction experiments. However, attempts to det ect the presence of the contaminant in the crystal by crystallographic structure refinement did not yield conclusive results.