_EC 6.3.-.- Forming carbon-nitrogen bonds. 819 PDB entries  
EC 6.-.-.- Ligases. [1,619 PDB entries]
EC 6.3.-.- Forming carbon-nitrogen bonds. [819 PDB entries]    
EC 6.3.1.- Acid--ammonia (or amide) ligases (amide synthases). [70 PDB entries]
EC 6.3.2.- Acid--amino-acid ligases (peptide synthases). [340 PDB entries]
EC 6.3.3.- Cyclo-ligases. [71 PDB entries]
EC 6.3.4.- Other carbon--nitrogen ligases. [255 PDB entries]
EC 6.3.5.- Carbon--nitrogen ligases with glutamine as amido-N-donor. [83 PDB entries]