THE SERINE ACETYLTRANSFERASE FROM ESCHERICHIA-COLI - OVER-EXPRESSION, PURIFICATION AND PRELIMINARY CRYSTALLOGRAPHIC ANALYSIS

An expression vector has been constructed which increases the expression of serine acetyltransferase (SAT) from E. coli to 17% of the soluble cell protein. A novel purification procedure, using dye-affinity chromatography, allows purification of SAT to homogeneity. The enzyme has been crystallised from polyethylene glycol, in the presence of L-cysteine (an inhibitor of SAT). The crystals which diffract to beyond 3.0 Angstrom resolution are of the tetragonal spacegroup P4(1)2(1)2 (or P4(3)2(1)2) with cell dimensions a = b = 123 Angstrom, c = 79 Angstrom. Since ultracentrifugation and gel-filtration experiments indicate that purified SAT is a tetramer, there appears to be one-half tetramer in the asymmetric unit (V(m) = 2.55 Angstrom 3/Da).