In this report, we structurally and biochemically characterized the unknown gene product SP1746 from Streptococcus pneumoniae serotype 4. Various crystal structures of SP1746 in the apo form and in complex with different nucleotides were determined. SP1746 is a globular protein, which belongs to the histidine-aspartate (HD) domain superfamily with two Fe³⁺ ions in the active site that are coordinated by key active site residues and water molecules. All nucleotides bind in a similar orientation in the active site with their phosphate groups anchored to the diiron cluster. Biochemically, SP1746 hydrolyzes different nucleotide substrates. SP1746 most effectively hydrolyzes diadenosine tetraphosphate (Ap4A) to two ADPs. Based on the aforementioned data, we annotated SP1746 as an Ap4A hydrolase, belonging to the YqeK family. Our in vitro data indicate a potential role for SP1746 in regulating Ap4A homeostasis, which requires validation with in vivo experiments in bacteria in the future.

在本报告中，我们对肺炎链球菌血清型 4的未知基因产物 SP1746 进行了结构和生化表征。确定了 SP1746 的 apo 形式和与不同核苷酸复合物的各种晶体结构。 SP1746 是一种球状蛋白，属于组氨酸-天冬氨酸 (HD) 结构域超家族，活性位点有两个 Fe ³⁺离子，由关键活性位点残基和水分子协调。所有核苷酸以相似的方向结合在活性位点，其磷酸基团锚定在二铁簇上。在生物化学上，SP1746 水解不同的核苷酸底物。 SP1746 最有效地将四磷酸二腺苷 (Ap4A) 水解为两种 ADP。基于上述数据，我们将SP1746注释为Ap4A水解酶，属于YqeK家族。我们的体外数据表明 SP1746 在调节 Ap4A 稳态中的潜在作用，这需要未来通过细菌体内实验进行验证。