Figure 1.

A, Diamond shaped SpeG crystals in ligand-free form were obtained in Tris pH 7.5, PEG 4000, and 0.2 M lithium sulfate. B, SpeG crystals grown in the presence of spermine and 30% ethanol produced small irregular crystals. Small single crystals could be mounted in the loop. C, Tertiary structure of BtSpeG monomer in cartoon format. Secondary structures including β-strands, α-helices, and connecting loops colored in purple, cyan and orange respectively. The BtSpeG protomer is comprised of a 7-stranded anti-parallel sheet, with the exception of parallel strands β5 and β6, wrapped around 4-α -helices. D, The secondary structure elements represent the N-acetyltransferase sequence motifs C (β1-α1), D (β2—β3), A (β4-α3) and B (β5-α4) highlighted in colored boxes in blue, green, red and brown, respectively. The least conserved secondary structure elements Motif C, β-strand 6 and β7 and helix α2, can be absent in some GNAT proteins. Topology of BtSpeG and associated primary sequence is presented in cartoon form. E, A dimer was present in the asymmetric unit of BtSpeG in ligand-free form. A spermine molecule positioned in the allosteric site is shown in stick mode (red), and modelled AcCoA molecule (yellow) is shown in the active site (yellow).