| Feature | NAALADL2 summary | Evidence/citation |
|---|---|---|
| Enzyme classification and family | NAALADL2 corresponds to glutamate carboxypeptidase III (GCPIII), a type II transmembrane, di-zinc metallopeptidase in the M28 peptidase family, M28B subfamily; it cleaves C-terminal glutamate from acidic dipeptide-like substrates (pqac-00000009) | (pqac-00000009) |
| Alternative names | N-acetylated-alpha-linked acidic dipeptidase-like 2; NAALADL2; glutamate carboxypeptidase III (GCPIII); historically also called NAALADase II in early literature (pqac-00000007, pqac-00000009) | (pqac-00000007, pqac-00000009) |
| Structural features | GCPIII is a type II transmembrane glycoprotein with a short intracellular N-terminus, a single membrane-spanning segment, and a large extracellular catalytic region. The extracellular portion forms homodimers, and each monomer contains protease-like, apical, and C-terminal/dimerization domains; the protein is N-glycosylated and structurally close to GCPII (pqac-00000009) | (pqac-00000009) |
| Primary substrates and products | Physiologically relevant substrates include NAAG, polyglutamylated folates (FolGluₙ), and β-citryl-L-glutamate (BCG). NAAG is hydrolyzed to N-acetyl-L-aspartate (NAA) + L-glutamate; FolGluₙ to folate + free L-glutamate; BCG to citrate + L-glutamate (pqac-00000007, pqac-00000008) | (pqac-00000007, pqac-00000008) |
| Substrate specificity: NAAG | GCPIII cleaves NAAG, but human GCPII processes NAAG with ~3-fold to >10-fold higher catalytic efficiency depending on reaction conditions; GCPIII nonetheless clearly retains NAAG-hydrolyzing activity (pqac-00000007) | (pqac-00000007) |
| Substrate specificity: FolGluₙ | GCPIII also cleaves polyglutamylated folates, but for FolGlu₂–₆ GCPII is almost two orders of magnitude more efficient. Cleavage of monoglutamylated folate (FolGlu₁) is more comparable between the two enzymes (pqac-00000008) | (pqac-00000008) |
| Substrate specificity: BCG | BCG is the clearest substrate preference distinguishing GCPIII from GCPII: human GCPII can process BCG only very weakly, whereas human GCPIII hydrolyzes it with 3–5 orders of magnitude greater efficiency, making BCG a functionally specific substrate of GCPIII (pqac-00000008) | (pqac-00000008) |
| Catalytic properties and metal sensitivity | GCPIII is a di-zinc metallopeptidase, but unlike GCPII it is metal-sensitive. For NAAG and FolGlu₁ cleavage, GCPIII activity can be stimulated by added Mn²⁺ or Zn²⁺ and inhibited by Ca²⁺; for BCG, the trend differs, with stimulation by Mn²⁺ or Ca²⁺ and inhibition by Zn²⁺. GCPII is comparatively metal-insensitive (pqac-00000007, pqac-00000008) | (pqac-00000007, pqac-00000008) |
| Comparison with FOLH1/GCPII: sequence identity and overall similarity | GCPIII/NAALADL2 and GCPII/FOLH1 share 67% amino-acid identity and 81% similarity, with highly similar overall 3D organization and catalytic architecture as homodimeric M28B glutamate carboxypeptidases (pqac-00000009) | (pqac-00000009) |
| Comparison with FOLH1/GCPII: key structural differences | Important active-site differences include lower zinc occupancy in GCPIII, linked to substitution of GCPII Asn519 by GCPIII Ser509, and absence in GCPIII of the GCPII arene-binding site because GCPII Trp541 is replaced by Lys531 in GCPIII. These changes alter ligand recognition, metal behavior, and substrate preference (pqac-00000007) | (pqac-00000007) |
| Key enzymatic differences from GCPII | Relative to GCPII, GCPIII has lower efficiency for NAAG and polyglutamyl folate hydrolysis, far greater activity toward BCG, distinct salt/pH optima, lower/variable Zn2 occupancy in the active site, and stronger dependence on divalent metal composition during catalysis (pqac-00000007, pqac-00000008) | (pqac-00000007, pqac-00000008) |
| Functional pathway implication | In cancer metabolomics, NAALADL2 has been interpreted as contributing with FOLH1 to NAAG-to-NAA conversion, potentially feeding NAA/NAAG-associated metabolic rewiring in castration-resistant prostate cancer; this is a pathway-level inference rather than a direct kinetic characterization in that study (pqac-00000005) | (pqac-00000005) |


*Table: This table summarizes the molecular function, structure, substrates, and catalytic behavior of human NAALADL2/GCPIII, including how it differs from the closely related enzyme FOLH1/GCPII. It is useful for quickly distinguishing experimentally supported enzymatic properties from broader pathway-level interpretations.*