Le Du Marie-Hélène, Millan Jose Luis
Département d'Ingénierie et d'Etudes des Protéines (DIEP), CEA, Bat 152 C. E. Saclay, 91191 Gif-sur-Yvette Cedex, France.
J Biol Chem. 2002 Dec 20;277(51):49808-14. doi: 10.1074/jbc.M207394200. Epub 2002 Oct 7.
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.
碱性磷酸酶（AP）基因家族的进化导致人类体内存在一种组织非特异性（TNAP）和三种组织特异性同工酶，即肠型（IAP）、生殖细胞型（GCAP）和胎盘型AP（PLAP）。为了确定这些同工酶之间的结构差异，我们基于PLAP(1)的1.8结构构建了TNAP、IAP和GCAP分子模型，并进行了比较结构分析。我们研究了单体-单体界面，因为该区域对蛋白质稳定性和酶活性至关重要。我们发现该界面允许IAP、GCAP和PLAP之间形成异二聚体，但TNAP与三种组织特异性同工酶中的任何一种之间都不能形成。其次，活性位点裂隙被划分为三个区域，即活性位点本身、裂隙顶部和裂隙底部。该分析得出了每种AP同工酶活性位点的结构指纹，这表明该同工酶家族在底物特异性方面存在差异。
