 This variety of function may be a means to create ligand-specific signals.This supports the notion that trafficking, a term for the modification of proteins subsequent to mRNA translation, may be vital to the function of receptor signaling.Included in a number of the structural features that can be recognized in all protein tyrosine kinases are an ATP binding site, three residues that are thought to be associated with the function of the third phosphate group (often called the gamma-phosphate group) of an ATP molecule bound to the enzyme, and a possible catalytic site of the enzyme that is an amino acid.