BIOCHEMISTRY OF ENERGY-DEPENDENT (INTRACELLULAR) PROTEIN DEGRADATION

调节蛋白的快速细胞内降解已经被证实是一种重要的生物学机制。 被认为是控制重要细胞的重要因素， 过程，如对热冲击和其他应力的反应， 细胞周期事件，DNA损伤的修复，以及适应 营养和环境条件。去年的研究表明， 主要集中在生物化学性质和体内功能的一个主要的 E. coli、Clp蛋白酶。clpP基因，编码 对于这种双组分蛋白酶的蛋白水解亚基， 被测序并显示是独一无二的。虽然与任何已知的 蛋白酶，Clp P具有广泛的氨基酸同源性的蛋白质未知 由植物叶绿体DNA编码的功能。免疫化学筛查 表明在多种组织中存在与Clp P密切相关的蛋白质， 其它细菌、酵母和其它低等真核生物，以及动物细胞。CLP P属于丝氨酸蛋白酶家族和两个活性位点残基， 其中Ser111和His136被鉴定。这些突变改变 残基消除了蛋白水解活性，同时允许适当的折叠， Clp P和与调节组分Clp A的结合相互作用。在 用纯化的Clp蛋白酶进行的体外研究表明，Clp P具有非常高的 与低分子量底物的弱内切蛋白水解活性， 由Clp A和ATP激活>100倍。CLP切割许多不同的 肽键和特异性不受调节 件.每个肽键大约有两个ATP分子被水解 劈开的Clp P的电子显微照片显示由两个 叠加的六边形环，这承担着惊人的相似之处， 在真核细胞中发现的ATP依赖性多催化蛋白酶。

The rapid intracellular degradation of regulatory proteins has been recognized as an important element in the control of vital cellular processes such as the response to heat shock and other stresses, the timing of cell cycle events, the repair of DNA damage, and the adaptation to nutritional and environmental conditions. Research over the last year has focused on the biochemical properties and in vivo functions of a major ATP-dependent protease from E. coli, Clp protease. The clpP gene, coding for the proteolytic subunit of this two-component protease, has been sequenced and shown to be unique. Although not closely related to any known proteases, Clp P has extensive amino acid homology to a protein of unknown function encoded by plant chloroplasts DNA. Immunochemical screening indicates the presence of proteins closely related to Clp P in a variety of other bacteria, yeast and other lower eukaryotes, and in animal cells. Clp P belongs to the serine protease family and two active site residues, Ser111 and His136, have been identified. Mutational alteration of these residues eliminates proteolytic activity while allowing proper folding of Clp P and binding interaction with the regulatory component, Clp A. In vitro studies with purified Clp protease revealed that Clp P has a very weak endoproteolytic activity with low molecular weight substrates and is activated >100 fold by Clp A and ATP. Clp cleaves a number of different peptide bonds and the specificity is not affected by the regulatory components. About two molecules of ATP are hydrolyzed per peptide bond cleaved. Electron micrographs of Clp P show a structure composed of two superimposed hexagonal rings, which bears a striking resemblance to the ATP-dependent multicatalytic protease found in eukaryotic cells.