1gtr is a 2 chain structure with sequence from Escherichia coli. The April 2001 RCSB PDB Molecule of the Month feature on Aminoacyl-tRNA Synthetases by David S. Goodsell is 10.2210/rcsb_pdb/mom_2001_4. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance.