Structural evidence of functional divergence in human alkaline phosphatases.
The evolution of the alkaline phosphatase (AP) gene family has lead to the existence in humans of one tissue-nonspecific (TNAP) and three tissue-specific isozymes, i.e. intestinal (IAP), germ cell (GCAP), and placental AP (PLAP). To define the structural differences between these isozymes, we have built models of the TNAP, IAP, and GCAP molecules based on the 1.8-structure of PLAP(1) and have performed a comparative structural analysis. We have examined the monomer-monomer interface as this area is crucial for protein stability and enzymatic activity. We found that the interface allows the formation of heterodimers among IAP, GCAP, and PLAP but not between TNAP with any of the three tissue-specific isozymes. Secondly, the active site cleft was mapped into three regions, i.e. the active site itself, the roof of the cleft, and the floor of the cleft. This analysis led to a structural fingerprint of the active site of each AP isozyme that suggests a diversification in substrate specificity for this isozyme family.
Le Du
Marie-Hélène
MH
Département d'Ingénierie et d'Etudes des Protéines (DIEP), CEA, Bat 152 C. E. Saclay, 91191 Gif-sur-Yvette Cedex, France. mhledu@cea.fr
Millan
Jose Luis
JL
D000469:Alkaline Phosphatase / Q000737:chemistry*; D000595:Amino Acid Sequence; D001665:Binding Sites; D002412:Cations; D019281:Dimerization; D005854:Germ Cells / Q000201:enzymology; D006801:Humans; D006860:Hydrogen Bonding; D007422:Intestines / Q000201:enzymology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D010766:Phosphorylation; D010920:Placenta / Q000201:enzymology; D011487:Protein Conformation; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
D002412:Cations; D020033:Protein Isoforms; D000469:Alkaline Phosphatase