Mathews I I, Erion M D, Ealick S E
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA.
Biochemistry. 1998 Nov 10;37(45):15607-20. doi: 10.1021/bi9815445.
Adenosine kinase (AK) is a key enzyme in the regulation of extracellular adenosine and intracellular adenylate levels. Inhibitors of adenosine kinase elevate adenosine to levels that activate nearby adenosine receptors and produce a wide variety of therapeutically beneficial activities. Accordingly, AK is a promising target for new analgesic, neuroprotective, and cardioprotective agents. We determined the structure of human adenosine kinase by X-ray crystallography using MAD phasing techniques and refined the structure to 1.5 A resolution. The enzyme structure consisted of one large alpha/beta domain with nine beta-strands, eight alpha-helices, and one small alpha/beta-domain with five beta-strands and two alpha-helices. The active site is formed along the edge of the beta-sheet in the large domain while the small domain acts as a lid to cover the upper face of the active site. The overall structure is similar to the recently reported structure of ribokinase from Escherichia coli [Sigrell et al. (1998) Structure 6, 183-193]. The structure of ribokinase was determined at 1.8 A resolution and represents the first structure of a new family of carbohydrate kinases. Two molecules of adenosine were present in the AK crystal structure with one adenosine molecule located in a site that matches the ribose site in ribokinase and probably represents the substrate-binding site. The second adenosine site overlaps the ADP site in ribokinase and probably represents the ATP site. A Mg2+ ion binding site is observed in a trough between the two adenosine sites. The structure of the active site is consistent with the observed substrate specificity. The active-site model suggests that Asp300 is an important catalytic residue involved in the deprotonation of the 5'-hydroxyl during the phosphate transfer.
腺苷激酶（AK）是调节细胞外腺苷和细胞内腺苷酸水平的关键酶。腺苷激酶抑制剂可将腺苷提升至能激活附近腺苷受体并产生多种治疗有益活性的水平。因此，AK是新型镇痛、神经保护和心脏保护药物的一个有前景的靶点。我们利用多波长反常散射（MAD）相位技术通过X射线晶体学确定了人腺苷激酶的结构，并将该结构精修至1.5埃分辨率。该酶结构由一个带有九条β链、八条α螺旋的大α/β结构域和一个带有五条β链、两条α螺旋的小α/β结构域组成。活性位点沿着大结构域中β折叠的边缘形成，而小结构域则作为盖子覆盖活性位点的上表面。整体结构与最近报道的大肠杆菌核糖激酶的结构相似[西格雷尔等人（1998年）《结构》6卷，183 - 193页]。核糖激酶的结构是在1.8埃分辨率下确定的，代表了碳水化合物激酶新家族的首个结构。AK晶体结构中有两个腺苷分子，其中一个腺苷分子位于与核糖激酶中核糖位点匹配的位置，可能代表底物结合位点。第二个腺苷位点与核糖激酶中的ADP位点重叠，可能代表ATP位点。在两个腺苷位点之间的凹槽中观察到一个Mg2 +离子结合位点。活性位点的结构与观察到的底物特异性一致。活性位点模型表明，天冬氨酸300是磷酸转移过程中参与5'-羟基去质子化的重要催化残基。
