Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Chemistry and Pharmacology
The signal recognition particle (SRP) of bacteria consists of only one protein, known as Ffh or the SRP54 homologue, which forms a complex with 4.5S RNA. It also binds to signal peptides and contains a GTPase which displays interesting differences to Ras GTPases. The conserved NG-domain of Ffh from the archaebacterium Acidianus ambivalens was cloned and overexpressed with a C-terminal His tag in Escherichia coli. Crystallization experiments of the native protein as well as of the Thr112Ala mutant, which is deficient in GTP hydrolysis, resulted in crystals suitable for X-ray diffraction. The crystals belong to the orthorhombic space group C2221, with unit-cell parameters a = 64.5, b = 128.3, c = 72.0 Å. At cryogenic temperatures, the crystals diffracted to a resolution limit of 2.8 Å using a rotating-anode generator and contain one molecule per asymmetric unit. A native data set has been collected using synchrotron radiation to around 2.0 Å resolution. Selenomethionine protein was produced; its crystals diffract in-house to about 2.8 Å resolution.
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