Structure of ligases
Like all enzymes, ligases are proteins which have an active site for the enzymatic reaction and a target molecule recognition site which gives the reaction its specificity.
Function of ligases
There are many types of ligase depending on the type of covalent bond which they catalyse (carbon-carbon bond, carbon-nitrogen bond, carbon-sulphur bond, etc.). They generally use the energy of a molecule of ATP (or GTP) to catalyse the reaction.
The ligases include aminoacyl tRNA-synthetases (which bind amino acids onto the corresponding tRNA and the DNA ligases (which bring two pieces ofDNA together).
Aminoacyl tRNA synthetase (in brown ) is a ligase which binds the amino acid covalently onto the corresponding tRNA (coloured). © Yikrazuul, Wikimedia, CC by-sa 3.0