Crystal Structure of Alkaline Phosphatase from Human Placenta at 1.8 Å Resolution

Abstract

Human placental alkaline phosphatase (PLAP) is one of three tissue-specific human APs extensively studied because of its ectopic expression in tumors. The crystal structure, determined at 1.8-Å resolution, reveals that during evolution, only the overall features of the enzyme have been conserved with respect to Escherichia coli. The surface is deeply mutated with 8% residues in common, and in the active site, only residues strictly necessary to perform the catalysis have been preserved. Additional structural elements aid an understanding of the allosteric property that is specific for the mammalian enzyme (Hoylaerts, M. F., Manes, T., and Millá n, J. L. (1997) J. Biol. Chem. 272, 22781-22787). Allostery is probably favored by the quality of the dimer interface, by a long N-terminal ␣-helix from one monomer that embraces the other one, and similarly by the exchange of a residue from one monomer in the active site of the other. In the neighborhood of the catalytic serine, the orientation of Glu-429, a residue unique to PLAP, and the presence of a hydrophobic pocket close to the phosphate product, account for the specific uncompetitive inhibition of PLAP by L-amino acids, consistent with the acquisition of substrate specificity. The location of the active site at the bottom of a large valley flanked by an interfacial crown-shaped domain and a domain containing an extra metal ion on the other side suggest that the substrate of PLAP could be a specific phosphorylated protein.

Surface density as a significant parameter for the enzymatic activity of two forms of alkaline phosphatase immobilized on phospholipid Langmuir–Blodgett films

“…Data recently reported for bovine intestinal alkaline phosphatase has shown that enzyme adsorption also occurs through the GPI anchor and that the major axis of the aminoacid moiety is parallel to the adsorption surface [15,[28][29][30]; they are in good agreement with our results. According to several authors, the anchor should be located opposite the catalytic site, on the face parallel to the major axis of the enzyme [30,56]. Consequently, DSAP is oriented with its major axis almost parallel to the interface.…”

A thermodynamic study of GPI-anchored and soluble form of alkaline phosphatase films at the air–water interface

“…1B). As the general shape of the protein may be assimilated to a 10 × 5 nm prolate ellipsoid of revolution [10], this molecular area is consistent with a protein oriented with its major axis parallel to the interface as defined by Narsimhan and Uraizee [49]. Actually, the protein area is then 40 nm 2 but some empty space has to be considered between AP molecules.…”

“…The structure of AP from human placenta, which presents about 90% sequence similarity with intestinal AP, has been solved by X-rays [10]. Each monomer shows a typical α/β topology with β-sheets at the center surrounded by α-helices oriented approximately in the same direction.…”

Clinical and ALPL Gene Mutations Analysis in an Early Onset Chinese Odontohypophosphatasia Patient

“…The protein encoded by ALPL contains 5 important domains [17,18]: activation domain, N-terminal coiled region, homodimer, crown domain and calcium binding site. Mutations around these sites may affect the activity of the protein.…”