1、Chapter 7 Protein sorting II- free-ribosome system secretory pathway 1.1 Synthesis and Targeting of Mitochondrial線粒體具有1000多種蛋白質(zhì)，其自身合成的僅十余種，因此大量蛋白質(zhì)是在細(xì)胞質(zhì)中合成的。 線粒體前體蛋白質(zhì)在在運(yùn)輸以前，以未折疊的形式存在，N端有一段信號(hào)序列稱為導(dǎo)肽或引肽，完成轉(zhuǎn)運(yùn)后被信號(hào)肽酶（signal peptidase）切除，就成為成熟蛋白，這種現(xiàn)象就叫做后轉(zhuǎn)譯（posttranslation）。信號(hào)肽的特點(diǎn)是： 多位于肽鏈的N端，由大約20個(gè)氨基酸構(gòu)成； 形成一

2、個(gè)兩性螺旋，帶正電荷的氨基酸殘基和不帶電荷的疏水氨基酸殘基分別位于螺旋的兩側(cè)； 對所牽引的蛋白質(zhì)沒有特異性要求。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線粒體轉(zhuǎn)運(yùn)與葉綠體非常相似1.2 Sort to Chloroplast Compartment葉綠體蛋白轉(zhuǎn)運(yùn)運(yùn)輸機(jī)理與線粒體的相似。如： 都發(fā)生后轉(zhuǎn)譯； 每一種膜上有特定的轉(zhuǎn)位因子； 具有接觸點(diǎn)（contact site）； 需要能量，同樣利用ATP和質(zhì)子動(dòng)力勢； 前體蛋白N端有信號(hào)序列，使用后被信號(hào)肽酶切除。 但兩者的蛋白質(zhì)轉(zhuǎn)運(yùn)體系中除了某些hsp分子相同外，轉(zhuǎn)位因子復(fù)合體是不同的。Import of rubisco small (S) s

4、ubunits into the chloroplast stroma 轉(zhuǎn)運(yùn)肽內(nèi)囊體膜蛋白轉(zhuǎn)運(yùn)需要兩段信號(hào)1.3 Synthesis and Targeting of Peroxisome Proteins 核基因合成，后轉(zhuǎn)運(yùn)方式運(yùn)輸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):核糖核蛋白顆粒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 核內(nèi)不均一核糖核蛋白 (heterogeneous ribonucleop