进一步诱导。
Hsp60的电镜三维镜象照片
3.2 functions of chaperones
◆帮助蛋白质折叠和装配
◆蛋白质的转运和定位 ◆参与细胞器和细胞核结构的发生 ◆应激反应
◆参与信号转导
Action of chaperones during translation
◆该概念有以下特点:
●凡具有“介导”功能的蛋白,都称为分子 伴侣,可以是完全不同的蛋白质;
●作用机理尚不清楚,故用“介导”二字,伸 缩性较大；
●分子伴侣一定不是最终结构的组成部分, 但不一定是一个分离的实体;
●装配的涵意比较广,包括:帮助新生肽的折 叠,越膜定位, 亚基组装等。
◆It is important to note that :
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3 分子伴侣(chaperones)
3.1 分子伴侣的发现及种类
◆The term “chaperone" was first used by Ron Laskey and his colleagues to describe a protein (nucleoplasmin) that is required for the assembly of nucleosomes from histones and DNA.
revised picture of nuclear structure
• Nuclear matrix: a proteinaceous scaffold-like network
• Nucleolus: the center for synthesis and processing of rRNA molecules
chromosomes nuclear matrix nucleoli nucleoplasm
an interphase HeLa cell nucleus
showing some of the major components of the nucleus
8.1.2 Internal Architecture
signals ,NLS) ◆核输出信号(nuclear export
signals, NES) ◆输入蛋白(importin) ◆输出蛋白(exportin)
核定位信号
Nuclear localization signals
核蛋白的输入 ◆核质蛋白(nucleoplasmin)实验 ◆核蛋白输入机理 ●输入蛋白 ●Ran蛋白:小GTPase
Protein import through NPC
Role of the Ran protein in nuclear import
核蛋白输入机理
核内RNA与蛋白质输 出
◆RNA的输出 ●异质核糖核蛋白 (heterogeneous
ribonucleoprotein, hnRNP) ●信使RNP(messenger RNP, mRNP) ●mRNA的输出 ◆核内蛋白质输出 ◆snRNA的输出
Transport of RNA between nucleus and cytoplasm
• active, energy-dependent process • ribonucleoprotein complexes rather
than naked RNAs
mRNA的输 出
核内蛋白质的输出
Molecular traffic through NPC
核孔的被动运输
Small molecular traffic through the NPC by passive diffusion
Small molecules and some proteins with MW< 50 kD pass freely across the nuclear envelope in either direction.
Chap 8 Nucleus and Chromosomes
• Nucleus of a Eukaryotic Cell • Nuclear Envelope • Nuclear Pore Complex • Chromatin • Nucleolus and Ribosome Biogenesis • Nuclear Matrix
Function of the nuclear envelope
❖ a barrier between the nucleus and cytoplasm, as a distinct biochemical compartment ❖ sole channels through the nuclear envelope
● Chaperones do not convey additional information required for the folding of polypeptides into their correct three-dimensional conformations.
● The folded conformation of a protein is determined solely by its amino acid sequence.
分 子 伴 侣 的 基 本 功 能
◆分子内伴侣(intromolecular chaperones)
◆分子伴侣的分布 ●从细菌到人,从动物到植物 ●细胞质、线粒体、叶绿体和微体
分子伴侣结构上的共同特点
◆家族成员具有高度保守性 ◆家族成员结构上具有相似性 ◆大部分在体内为组成型表达,在刺激条件下会被
8.1 The Nucleus of a Eukaryotic Cell
Surrounded by two concentric membranes ❖The inner nuclear membrane ❖ The outer nuclear membrane
8.1.1 Organization of the Nucleus
8.3 Nuclear Pore Complex
• Vertebrate: 50100 proteins • Diameter: 120 nm, 125 MDa • basketlike apparatus • eightfold symmetry
Composition of the NPC
• Cytoplasmic ring • Nuclear ring • Spoke • Central plug
● Rather, chaperones catalyze protein folding by assisting the self-assembly process.
●They appear to function by binding to and stabilizing unfolded or partially folded polypeptides that are intermediates along the pathway leading to the final correctly folded state.
The first step does not require energy, proteins that contain NLSs bind to the NPC but do not pass through the pore.
The second step is an energy-dependent process that requires GTP hydrolysis.
RanGAP:RanGTP激活蛋白:细胞质 中 RCC1：Ran nucleotideexchange factor1.细胞核中
核质 素的 核定 位信 号及 其作
用
Receptors for the NLS transport proteins to the nucleus
Protein import through the NPC can be divided into two steps, distinguished by whether they require energy.
Structure of the nuclear envelope
• outer nuclear membrane • inner nuclear membrane • nuclear lamina • perinuclear space • nuclear pore
nuclear lamina
Nuclear envelopes of Xenopus oocytes visualized by field emission in-lens SEM
Cut-away model of the NPC
Three-dimensional models of the NPC
❖ A structure with eightfold symmetry ❖ The NPC consists of an assembly of eight spokes arranged around a central channel
8.2 The Nuclear Envelope
• The separation of a cell’s genetic material from the surrounding cytoplasm may be single most important feature that distinguishes eukaryotes from prokaryotes.
❖ The spokes are connected to rings at the nuclear and cytoplasmic surfaces
Electron micrograph of NPC
NLSs direct nuclear proteins to the nucleus