1gtp is a 20 chain structure with sequence from Escherichia coli. The August 2015 RCSB PDB Molecule of the Month feature on Tetrahydrobiopterin Biosynthesis by David Goodsell is 10.2210/rcsb_pdb/mom_2015_8. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance.