PDF(Pubmed)
Abstract：
Glutaminyl-peptide cyclotransferases (QCs) convert the N-terminal glutamine or glutamate residues of protein and peptide substrates into pyroglutamate (pE) by releasing ammonia or a water molecule. The N-terminal pE modification protects peptides/proteins against proteolytic degradation by amino- or exopeptidases, increasing their stability. Mammalian QC is abundant in the brain and a large amount of evidence indicates that pE peptides are involved in the onset of neural human pathologies such as Alzheimer\'s and Huntington\'s disease and synucleinopathies. Hence, human QC (hQC) has become an intensively studied target for drug development against these diseases. Soon after its characterization, hQC was identified as a Zn-dependent enzyme, but a partial restoration of the enzyme activity in the presence of the Co(II) ion was also reported, suggesting a possible role of this metal ion in catalysis. The present work aims to investigate the structure of demetallated hQC and of the reconstituted enzyme with Zn(II) and Co(II) and their behavior in the presence of known inhibitors. Furthermore, our structural determinations provide a possible explanation for the presence of the mononuclear metal binding site of hQC, despite the presence of the same conserved metal binding motifs present in distantly related dinuclear aminopeptidase enzymes.
摘要：
谷氨酰胺肽环转移酶（QC）通过释放氨或水分子将蛋白质和肽底物的N末端谷氨酰胺或谷氨酸残基转化为焦谷氨酸（pE）。N末端pE修饰保护肽/蛋白质免受氨基或外肽酶的蛋白水解降解，提高其稳定性。哺乳动物QC在大脑中丰富，大量证据表明pE肽参与神经人类病理的发作，例如阿尔茨海默氏病和亨廷顿氏病以及突触核蛋白病。因此，人类QC（hQC）已成为针对这些疾病的药物开发的深入研究目标。在其表征后不久，hQC被鉴定为锌依赖性酶，但也报道了在Co（II）离子存在下酶活性的部分恢复，表明这种金属离子在催化中的可能作用。本工作旨在研究脱金属hQC的结构以及具有Zn（II）和Co（II）的重构酶的结构及其在已知抑制剂存在下的行为。此外，我们的结构测定为hQC的单核金属结合位点的存在提供了可能的解释，尽管在远缘相关的双核氨肽酶中存在相同的保守金属结合基序。
