Aminopeptidase

From Proteopedia

Aminopeptidases catalyze a release of an N-terminal amino acid from a peptide, amide, or arylamide.

S. griseus aminopeptidase

S. griseus Aminopeptidase (SGAP) cleaves the N-terminal amino acid from a peptide or protein, and is specific for larger hydrophobic acids, especially leucine. No cleavage occurs if the next residue is proline.

The active site of the enzyme contains two Zn2+ ions with His85 and Asp160 as ligands for one ion, and Glu132 and His247 as ligands for the second ion. Asp97 is a common ligand to both ions. What appears to be a phosphate anion is bound to both zinc atoms, replacing the water molecule/hydroxide ion normally found in this class of enzyme.

The enzyme's activity is modulated by Calcium cations. This structure revealed a calcium binding site near the N-terminus, involving Ile4, Asp262, Asp266, two water molecules, and Asp3. This site, however, is quite distant from the active site, and it was unclear how this might modulate enzymatic activity.