Structure
The three domains of the extracellular portion of GCPII –the protease, apical and C-terminal domains- collaborate in substrate recognition. The protease domain is a central seven-stranded mixed β-sheet. The β-sheet is flanked by 10 α-helices. The apical domain is located between the first and the second strands of the central β-sheet of the protease domain. The apical domain creates a pocket that facilitates substrate binding. The C-terminal domain is an Up-Down-Up-Down four-helix bundle.
The central pocket is approximately 2 nanometres in depth and opens from the extracellular space to the active site. This active site contains two zinc ions. During inhibition, each acts as a ligand to an oxygen in 2-PMPA or phosphate.
There is also one calcium ion coordinated in GCPII, far from the active site. It has been proposed that calcium holds together the protease and apical domains.
In addition, ten glycosylation sites have been identified in human GCPII. Glycosylation far from the catalytic domain still affects the ability of GCPII to hydrolyze NAAG.
Read more about this topic: Glutamate Carboxypeptidase II
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