蛋白质分选下课件

1、Chapter 7 Protein sorting II- free-ribosome system secretory pathway 1.1 Synthesis and Targeting of Mitochondrial线粒体具有1000多种蛋白质，其自身合成的仅十余种，因此大量蛋白质是在细胞质中合成的。 线粒体前体蛋白质在在运输以前，以未折叠的形式存在，N端有一段信号序列称为导肽或引肽，完成转运后被信号肽酶（signal peptidase）切除，就成为成熟蛋白，这种现象就叫做后转译（posttranslation）。信号肽的特点是： 多位于肽链的N端，由大约20个氨基酸构成； 形成一

2、个两性螺旋，带正电荷的氨基酸残基和不带电荷的疏水氨基酸残基分别位于螺旋的两侧； 对所牵引的蛋白质没有特异性要求。MatrixOuter membraneIntermembrane spaceCross section of mitochondrionInner membraneMitochondrial Proteins That Are Synthesized in the CytosolProteins Are Targeted to Sub-mitochondrial Compartments Protein import into mitochondriaProtein Transpo

3、rt into Inner Membrane and Intermembrane Space Requires Two Signal Sequences线粒体转运与叶绿体非常相似1.2 Sort to Chloroplast Compartment叶绿体蛋白转运运输机理与线粒体的相似。如： 都发生后转译； 每一种膜上有特定的转位因子； 具有接触点（contact site）； 需要能量，同样利用ATP和质子动力势； 前体蛋白N端有信号序列，使用后被信号肽酶切除。 但两者的蛋白质转运体系中除了某些hsp分子相同外，转位因子复合体是不同的。Import of rubisco small (S) s

4、ubunits into the chloroplast stroma 转运肽内囊体膜蛋白转运需要两段信号1.3 Synthesis and Targeting of Peroxisome Proteins 核基因合成，后转运方式运输C- and N-Terminal Targeting SequencesPTS1PTS21.4 Protein sort to nucleusThe nuclear pore complex0.1um Side view of nuclear pore1.4.1Nuclear protein transport mechanism nuclear localiz

5、ation signals ,NLSnuclear export signals, NESimportinexportin Mechanism of protein importProteins selected for import into nucleus have a nuclear localization signal (NLS) e.g.-Pro-Pro-Lys-Lys-Lys-Arg-NLS is recognized by cytosolic nuclear import receptors which bind to nuclear pore fibrils extendin

6、g into cytosolPore opens and protein plus import receptor enter nucleus. Import receptor exported for re-useNuclear localization signals Nuclear localisation signal (NLS)Nuclear localization signals Nucleoplasmin label and injection Nucleoplasmin location effect Mechanism of transport through nuclea

7、r poresNLS need not cut after transport Nuclear importProtein transport by nucleus pore complexTransport is selective Restrict transport particle Require energy expenditure saturated dynamic Transport is double direction Import and export 1.4.2 Mechanism of export from nucleusMost of traffic moving

8、out of nucleus consists of different types of RNA moleculesRNA moves through nuclear pore as complex of ribonucleoprotein (RNP):核糖核蛋白颗粒Protein component of RNP contains a nuclear export signal (NES) that is recognised by export proteinsmRNA is bound by hnRNP only after fully spliced so only mature RNA is exportednuclear RNA and protein export mRNA export 核内不均一核糖核蛋白 (heterogeneous ribonucleop