Smurfit Institute of Genetics, Trinity College Dublin, Dublin 2, Ireland.
Plant J. 2010 Mar;61(5):741-51. doi: 10.1111/j.1365-313X.2009.04099.x. Epub 2009 Dec 9.
The N-end rule relates the in vivo half-life of a protein to the identity of its N-terminal amino acid residue. While some N-terminal residues result in metabolically stable proteins, other, so-called destabilizing residues, lead to rapid protein turnover. The N-end rule pathway, which mediates the recognition and degradation of proteins with N-terminal destabilizing residues, is present in all organisms examined, including prokaryotes. This protein degradation pathway has a hierarchical organization in which some N-terminal residues, called primary destabilizing residues, are directly recognized by specific ubiquitin ligases. Other destabilizing residues, termed secondary and tertiary destabilizing residues, require modifications before the corresponding proteins can be targeted for degradation by ubiquitin ligases. In eukaryotes, the N-end rule pathway is a part of the ubiquitin/proteasome system and is known to play essential roles in a broad range of biological processes in fungi, animals and plants. While the structure of the N-end rule pathway has been extensively studied in yeast and mammals, knowledge of its organization in plants is limited. Using both tobacco and Arabidopsis, we identified the complete sets destabilizing and stabilizing N-terminal residues. We also characterized the hierarchical organization of the plant N-end rule by identifying and determining the specificity of two distinct N-terminal amidohydrolases (Nt-amidases) of Arabidopsis that are essential for the destabilizing activity of the tertiary destabilizing residues Asn and Gln. Our results indicate that both the N-end rule itself and mechanistic aspects of the N-end rule pathway in angiosperms are very similar to those of mammals.
N 端规则将蛋白质的体内半衰期与其 N 端氨基酸残基的身份联系起来。虽然一些 N 端残基导致代谢稳定的蛋白质，但其他所谓的不稳定残基则导致蛋白质快速周转。介导具有 N 端不稳定残基的蛋白质识别和降解的 N 端规则途径存在于所有被研究的生物体中，包括原核生物。这种蛋白质降解途径具有分层组织，其中一些 N 端残基，称为主要不稳定残基，被特定的泛素连接酶直接识别。其他不稳定残基，称为二级和三级不稳定残基，需要修饰才能被泛素连接酶靶向降解相应的蛋白质。在真核生物中，N 端规则途径是泛素/蛋白酶体系统的一部分，已知在真菌、动物和植物中广泛的生物学过程中发挥着重要作用。虽然 N 端规则途径的结构已在酵母和哺乳动物中进行了广泛研究，但对其在植物中的组织知之甚少。我们使用烟草和拟南芥鉴定了完整的不稳定和稳定的 N 端残基集。我们还通过鉴定和确定两种不同的拟南芥 N 端酰胺水解酶（Nt-酰胺酶）的特异性来表征植物 N 端规则的分层组织，这两种酶对于三级不稳定残基 Asn 和 Gln 的不稳定活性是必需的。我们的结果表明，被子植物的 N 端规则本身及其 N 端规则途径的机制方面与哺乳动物非常相似。
