Aminotripeptidase (peptidase T) from Salmonella typhimurium and a derivativ
e carrying a C-terminal His tag have been crystallized. In both cases, the
space group was found to be C2, with a single molecule in the asymmetric un
it. Crystals of the native peptidase T diffract to 2.9 Angstrom, but a sele
nomethionine derivative of this protein did not yield good crystals. Crysta
ls of the His-tag peptidase T diffracted to 2.6 Angstrom, however, and coul
d be used for the production of good-quality selenomethionine crystals. All
15 methionines, a native metal ion and two mercury reactive sites could be
located and crystals suitable for MAD data collection have been produced.