Department of Biochemistry and Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montreal, Canada.
FEBS J. 2017 Nov;284(21):3718-3726. doi: 10.1111/febs.14266. Epub 2017 Sep 30.
The ecto-nucleotide pyrophosphatase/phosphodiesterase (NPP) family of proteins mediates purinergic signaling by degrading extracellular nucleotides and also participates in phospholipid metabolism. NPP5 (ENPP5) is the least characterized member of this group and its specific role is unknown. This enzyme does not display activity on certain nucleotides and on other typical NPP substrates. In order to gain insights into its function, we determined the crystal structure of human and murine NPP5. Structural comparison with close homologs revealed a key phenylalanine to tyrosine substitution that prevents efficient hydrolysis of nucleotide diphosphates and triphosphates; reversal of this mutation enabled degradation of these molecules. Interestingly, NPP5 is able to cleave nicotinamide adenine dinucleotide (NAD), suggesting a potential role of this enzyme in NAD-based neurotransmission. An NPP5-specific metal binding motif is found adjacent to the active site, although its significance is unclear. These findings expand our understanding of substrate specificity within the NPP family.
Structural data are available in the Protein Data Bank under the accession numbers 5VEM, 5VEN, and 5VEO.
外核苷酸焦磷酸酶/磷酸二酯酶 (NPP) 蛋白家族通过降解细胞外核苷酸来介导嘌呤能信号转导，还参与磷脂代谢。NPP5（ENPP5）是该组中特征性最低的成员，其具体作用尚不清楚。该酶对某些核苷酸和其他典型的 NPP 底物没有活性。为了深入了解其功能，我们测定了人源和鼠源 NPP5 的晶体结构。与近缘同源物的结构比较揭示了一个关键的苯丙氨酸到酪氨酸取代，该取代阻止了核苷酸二磷酸和三磷酸的有效水解；该突变的逆转使这些分子能够被降解。有趣的是，NPP5 能够切割烟酰胺腺嘌呤二核苷酸 (NAD)，表明该酶在 NAD 为基础的神经递质传递中可能发挥作用。在活性位点附近发现了一个特定于 NPP5 的金属结合基序，尽管其意义尚不清楚。这些发现扩展了我们对 NPP 家族中底物特异性的理解。
结构数据可在蛋白质数据库 (PDB) 中以 5VEM、5VEN 和 5VEO 的条目号获得。
