Structural evidence for a functional role of human tissue nonspecific alkaline phosphatase in bone mineralization
Structural evidence for a functional role of human tissue nonspecific alkaline phosphatase in bone mineralization
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DOI：
10.1074/jbc.m102788200
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发表时间：
2001-08-17
影响因子：
4.8
通讯作者：
Le Du, MH
中科院分区：
文献类型：
--
作者：
Mornet, E;Stura, E;Le Du, MH
人类组织非特异性碱性磷酸酶（TNAP）存在于肝脏、肾脏和骨骼中。TNAP基因突变可导致低磷酸酶症，这是一种罕见的先天性疾病，其特征是骨矿化缺陷。TNAP与人胎盘碱性磷酸酶（PLAP）具有74%的同源性，其晶体结构最近已在原子分辨率下确定（Le Du，M. H、Stigbrand，T.，陶西格湾J.，Menez，A.，和Stura，E. A.（2001）J. Biol. Chem，276，9158 -9165）。同源性的程度使我们能够建立一个可靠的TNAP模型，以研究与低磷酸酶相关的突变之间的关系，以及它们对酶的活性或结构的可能后果。突变聚集在五个关键区域内，即活性位点及其附近、活性位点谷、同二聚体界面、冠状结构域和金属结合位点。冠域和金属结合域是PLAP结构中第一次观察到的，并且是PLAP特异性的。冠状结构域含有胶原结合环。同步辐射X射线荧光研究证实，在金属结合位点的金属是钙离子。TNAP中的几个严重突变发生在该钙位点周围，表明钙可能对TNAP功能至关重要。这个额外的金属结合位点的存在为钙的争议性作用提供了新的见解。
The human tissue nonspecific alkaline phosphatase (TNAP) is found in liver, kidney, and bone. Mutations in the TNAP gene can lead to Hypophosphatasia, a rare inborn disease that is characterized by defective bone mineralization. TNAP is 74% homologous to human placental alkaline phosphatase (PLAP) whose crystal structure has been recently determined at atomic resolution (Le Du, M. H., Stigbrand, T., Taussig, M. J., Menez, A., and Stura, E. A. (2001) J. Biol. Chem, 276,9158-9165). The degree of homology allowed us to build a reliable TNAP model to investigate the relationship between mutations associated with hypophosphatasia and their probable consequences on the activity or the structure of the enzyme. The mutations are clustered within five crucial regions, namely the active site and its vicinity, the active site valley, the homodimer interface, the crown domain, and the metal-binding site. The crown domain and the metal-binding domain are mammalian-specific and were observed for the first time in the PLAP structure. The crown domain contains a collagen binding loop. A synchrotron radiation x-ray fluorescence study confirms that the metal in the metal-binding site is a calcium ion. Several severe mutations in TNAP occur around this calcium site, suggesting that calcium may be of critical importance for the TNAP function. The presence of this extra metal-binding site gives new insights on the controversial role observed for calcium.