Department of Structural Biology, Weizmann Institute of Science, Rehovot, Israel.
PLoS One. 2012;7(11):e50649. doi: 10.1371/journal.pone.0050649. Epub 2012 Nov 28.
The mimivirus genome contains many genes that lack homologs in the sequence database and are thus known as ORFans. In addition, mimivirus genes that encode proteins belonging to known fold families are in some cases fused to domain-sized segments that cannot be classified. One such ORFan region is present in the mimivirus enzyme R596, a member of the Erv family of sulfhydryl oxidases. We determined the structure of a variant of full-length R596 and observed that the carboxy-terminal region of R596 assumes a folded, compact domain, demonstrating that these ORFan segments can be stable structural units. Moreover, the R596 ORFan domain fold is novel, hinting at the potential wealth of protein structural innovation yet to be discovered in large double-stranded DNA viruses. In the context of the R596 dimer, the ORFan domain contributes to formation of a broad cleft enriched with exposed aromatic groups and basic side chains, which may function in binding target proteins or localization of the enzyme within the virus factory or virions. Finally, we find evidence for an intermolecular dithiol/disulfide relay within the mimivirus R596 dimer, the first such extended, intersubunit redox-active site identified in a viral sulfhydryl oxidase.
拟菌病毒基因组包含许多在序列数据库中没有同源物的基因，因此被称为 ORFan 基因。此外，编码属于已知折叠家族的蛋白质的拟菌病毒基因在某些情况下与不能分类的、具有域大小的片段融合。拟菌病毒 R596 酶就是这样一个 ORFan 区域，它是硫氧还蛋白 Erv 家族的成员。我们测定了全长 R596 的一个变体的结构，观察到 R596 的羧基末端区域呈现折叠、紧凑的结构域，这表明这些 ORFan 片段可以是稳定的结构单元。此外，R596 的 ORFan 结构域折叠是新颖的，暗示着在大型双链 DNA 病毒中可能还有尚未发现的丰富的蛋白质结构创新。在 R596 二聚体的背景下，ORFan 结构域有助于形成一个富含暴露芳香族基团和碱性侧链的宽阔裂缝，该裂缝可能在结合靶蛋白或酶在病毒工厂或病毒粒子中的定位中发挥作用。最后，我们在拟菌病毒 R596 二聚体中发现了分子间二硫键/ 巯基氧化还原中继的证据，这是在病毒硫氧还蛋白中首次发现的这种扩展的、亚基间的氧化还原活性位点。
