Structure of N-formylglycinamide ribonucleotide amidotransferase II (PurL) from Thermus thermophilus HB8.

The crystal structure of PurL from Thermus thermophilus HB8 (TtPurL; TTHA1519) was determined in complex with an adenine nucleotide, PO4 3− and Mg2+ at 2.35 A resolution. TtPurL consists of 29 α-helices and 28 β-strands, and one loop is disordered. TtPurL consists of four domains, A1, A2, B1 and B2, and the structures of the A1–B1 and A2–B2 domains were almost identical to each other. Although the sequence identity between TtPurL and PurL from Thermotoga maritima (TmPurL) is higher than that between TtPurL and the PurL domain of the large PurL from Salmonella typhimurium (StPurL), the secondary structure of TtPurL is much more similar to that of StPurL than to that of TmPurL.