I should like to point out here that almost ANY protein will pick up something from the crystallization solution (cations, anions). Unfortunately, in the majority of cases these partially occupied ions will not be seen or will be mistakenly interpreted as water molecules. One way to 'see' such things is to carefully inspect an anomalous difference Fourier electron density map from good quality data collected at longer wavelength (even CuKa is good enough for that.
See: Mueller-Dieckmann et al (2007). Acta Cryst D63, 366-380. A most spectacular example is the recent PDB entry 2RKP, where at least 16 chlorides have been identified based on a data set collected at a wavelength of 2.0 A. Cheers, Manfred. ******************************************************************** * * * Dr. Manfred S. Weiss * * * * Team Leader * * * * EMBL Hamburg Outstation Fon: +49-40-89902-170 * * c/o DESY, Notkestr. 85 Fax: +49-40-89902-149 * * D-22603 Hamburg Email: [EMAIL PROTECTED] * * GERMANY Web: www.embl-hamburg.de/~msweiss/ * * * ********************************************************************
