Bujnicki Janusz M, Prigge Sean T, Caridha Diana, Chiang Peter K
Bioinformatics Laboratory, International Institute of Molecular and Cell Biology, Warsaw, Poland.
Proteins. 2003 Sep 1;52(4):624-32. doi: 10.1002/prot.10446.
S-adenosylhomocysteine hydrolase (SAHH) is a key regulator of S-adenosylmethionine-dependent methylation reactions and an interesting pharmacologic target. We cloned the SAHH gene from Plasmodium falciparum (PfSAHH), with an amino acid sequence agreeing with that of the PlasmoDB genomic database. Even though the expressed recombinant enzyme, PfSAHH, could use 3-deaza-adenosine (DZA) as an alternative substrate in contrast to the human SAHH, it has a unique inability to substitute 3-deaza-(+/-)aristeromycin (DZAri) for adenosine. Among the analogs of DZA, including neplanocin A, DZAri was the most potent inhibitor of the PfSAHH enzyme activity, with a K(i) of about 150 nM, whether Ado or DZA was used as a substrate. When the same DZA analogs were tested for their antimalarial activity, they also inhibited the in vitro growth of P. falciparum parasites potently. Homology-modeling analysis revealed that a single substitution (Thr60-Cys59) between the human and malarial PfSAHH, in an otherwise similar SAH-binding pocket, might account for the differential interactions with the nucleoside analogs. This subtle difference in the active site may be exploited in the development of novel drugs that selectively inhibit PfSAHH. We performed a comprehensive phylogenetic analysis of the SAHH superfamily and inferred that SAHH evolved in the common ancestor of Archaea and Eukaryota, and was subsequently horizontally transferred to Bacteria. Additionally, an analysis of the unusual and uncharacterized AHCYL1 family of the SAHH paralogs extant only in animals reveals striking divergence of its SAH-binding pocket and the loss of key conserved residues, thus suggesting an evolution of novel function(s).
S-腺苷同型半胱氨酸水解酶（SAHH）是S-腺苷甲硫氨酸依赖性甲基化反应的关键调节因子，也是一个有趣的药理学靶点。我们从恶性疟原虫中克隆了SAHH基因（PfSAHH），其氨基酸序列与疟原虫基因组数据库中的一致。尽管与人类SAHH不同，表达的重组酶PfSAHH可以使用3-脱氮腺苷（DZA）作为替代底物，但它却独特地无法用3-脱氮-（+/-）阿瑞司他霉素（DZAri）替代腺苷。在包括奈普拉霉素A在内的DZA类似物中，无论使用Ado还是DZA作为底物，DZAri都是PfSAHH酶活性最有效的抑制剂，其抑制常数（K(i)）约为150 nM。当测试相同的DZA类似物的抗疟活性时，它们也能有效抑制恶性疟原虫的体外生长。同源建模分析表明，在人源和疟原虫源的PfSAHH之间，在其他方面相似的SAH结合口袋中有一个单氨基酸替换（Thr60-Cys59），这可能解释了与核苷类似物的不同相互作用。活性位点的这种细微差异可用于开发选择性抑制PfSAHH的新型药物。我们对SAHH超家族进行了全面的系统发育分析，推断SAHH在古菌和真核生物的共同祖先中进化，随后水平转移到细菌中。此外，对仅存在于动物中的SAHH旁系同源物中不寻常且未表征的AHCYL1家族的分析表明，其SAH结合口袋存在显著差异，关键保守残基缺失，因此暗示了新功能的进化。
