Department of Neuroscience and Cell Biology, The University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555-0620, USA.
J Mol Biol. 2010 Jul 23;400(4):665-74. doi: 10.1016/j.jmb.2010.05.023. Epub 2010 May 19.
Protein supra-domains are defined as recurring arrangements of two or three domains present adjacent to each other along a polypeptide chain. Such combinations have novel functions beyond those of the individual partner domains that compose them, which can exist in isolation. Here, we describe a new type of large supra-domain (approximately 360 residues) in which one of the component partners (approximately 200 residues) appears to be incapable of existing in a context other than immediately adjacent to the C-terminus of the well-characterized Hsp90-like ATPase domain. We found that this supra-domain has a broad phylogenetic distribution, with examples in Archaea, Bacteria, and Eukarya. There is strong selective pressure for this arrangement to occur as part of repeated regions of unprecedented length. We identified multiple strategies of convergent evolution to attain such configurations. In humans, this supra-domain is present in triplicate at the N-terminus of the protein sacsin (4579 residues), mutated in the neurodegenerative disorder known as spastic ataxia of Charlevoix-Saguenay, and thus, we termed it "sacsin repeating region" (SRR). Biochemical characterization demonstrated that SRRs possess ATPase activity, which appears to be a requirement for sacsin function, as a disease-causing mutation leads to an alternate conformation completely incapable of hydrolyzing ATP. We also found evidence of a convergent evolutionary strategy to place SRRs in proteins containing C-terminal J domains, which we demonstrated here to be capable of stimulating the intrinsic ATPase activity of Hsp70. Our sequence and biochemical analyses indicate that SRRs necessitate nucleotide hydrolysis for their function, provided by the common Hsp90 ATPase domain, which, when coupled to the unique adjacent sequence, may give rise to a novel activity related to protein quality control.
蛋白质超结构域被定义为沿着多肽链彼此相邻存在的两个或三个结构域的重复排列。这种组合具有超越其组成的单个伙伴结构域的新颖功能，这些结构域可以独立存在。在这里，我们描述了一种新型的大型超结构域（约 360 个残基），其中一个组成伙伴（约 200 个残基）似乎无法存在于与其紧邻的特征性 Hsp90 样 ATP 酶结构域的 C 端以外的环境中。我们发现这种超结构域具有广泛的系统发育分布，在古菌、细菌和真核生物中都有例子。这种排列发生的选择压力很强，因为它是前所未有的重复区域的一部分。我们确定了多种趋同进化策略来达到这种构象。在人类中，这种超结构域存在于蛋白 sacsin 的 N 端重复三次（4579 个残基），在已知的神经退行性疾病痉挛性共济失调-沙格奈中突变，因此，我们将其命名为“sacsin 重复区”（SRR）。生化特性表明，SRRs 具有 ATP 酶活性，这似乎是 sacsin 功能的要求，因为致病突变导致完全不能水解 ATP 的替代构象。我们还发现了一种趋同进化策略的证据，即将 SRRs 放置在含有 C 端 J 结构域的蛋白中，我们在这里证明它们能够刺激 Hsp70 的固有 ATP 酶活性。我们的序列和生化分析表明，SRRs 需要核苷酸水解才能发挥其功能，这是由常见的 Hsp90 ATP 酶结构域提供的，当与独特的相邻序列结合时，可能会产生与蛋白质质量控制相关的新活性。
