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Chapter 5.5 Protein sorting
The Structure of Proteins
Proteins consist of one or more polypeptide chains. A
polypeptide consists of a series of amino acids joined
ny peptide bonds. These chains are folded in a very
precise fashion and if this folding is abolished than the
protein generally becomes non-functional.
Secondary and tertiary structure
Typically the three dimensional structure of a protein is
composed of a series of fairly rigid sections strongly
stabilised by hydrogen bonds (mainly alpha-helix and
beta pleated sheet) and flexible zones.
The flexibility means that a molecule binding at one point
on the surface of the protein will produce sympathetic
changes at other points, in particular in the sites which
bind the substrate and catalyse the reaction.
5.5.1 Signal hypothesis
1 signal peptide
exist in N-protein
16-26 aa,including hydrophobic center, Nprotein and C-protein
信号肽的一级序列
信号肽一级序列由疏水核心（h）、C端（c）和N端（n）三个区域
构成。
信号假说
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蛋白质的合成的命运决定于其氨基酸序列，在氨
基酸序列中包含有分选信号 的，便转移到内质
网膜上进行合成，这一分选信号称为信号肽。因
此凡是附着到ER膜的核蛋白体，必然在它转译的
肽链中包含一个氨基酸序列，作为信号指导游离
的核蛋白体附着到ER膜的表面，并结合于该处；
核蛋白体所转译的肽链中没有这样一个信号序列，
就留在胞液中。
Signal hypothesis
Cotrnaslocation :
Synthesis and transport occurred at
the same time
Start transfer sequence:
lead peptide go through ER
Stop transfer sequence:
stop-transfer signal
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Hydrophobic center of
peptide,peptide have one or more
stop-transfer signal,it can locate middle or
end of the peptide
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N-signal peptide is start-transfer
signal ，if located in the middle,
consider internal signal peptide
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As for mitochodria and
Signal petide was named leader petide
post translocation:
after protein synthesised in the cytosol,then transferd
to organelle,so refered post translocation
In the process of protein transmembrane,need ATP to
get rid of fold ,and some proteins to help to fold
functional proteins
信号识别颗粒
(signal-recognition particle, SRP)
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由6个多肽的亚单位加上小的RNA分子构成的复
合物。
在信号肽序列被翻译后，SRP的一端结合的新生
多肽链的信号肽，另一端结合到核蛋白体并停止
翻译。
从SRP结合到核蛋白体直到SRP-核蛋白体复合
物结合到内质网膜上SRP受体的时间内，翻译是
停止的，只有在SRP-核蛋白体复合物结合到膜
上的SRP受体后，翻译才重新开始。
SRP受体（SRP receptor）
是内质网膜上的一种停泊蛋白(docking
protein, DP)，即是一种膜的整合蛋白，
暴露在胞液面，一旦它与SRP-核蛋白体复
合物结合，SRP即被释放，翻译开始并通
过内质网膜上的转移器，转移生长的多肽
链横过膜
5.5.2 Basic pathway and type of protein
sorting
post transloction:
polypeptide completed synthesis in the
cytosol,and then transfer into orther
organelle
co-translation:
 After Protein start synthesis,peptiede transfer
to RER, protein synthesis company with
tansfering to RER cavity
 蛋白质合成起始后转移至粗面内质网中，新生肽边合
成边转入粗面内质网腔中
protein sorting signal
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Signal peptide
ER Retrivieval signal(KDEL)
Leader peptide for mitochondria
Nucleus location signal
蛋白质的转移方式
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膜内可溶性蛋白质的转移：多肽链通过内
质网膜是随着翻译同时转移到内质网腔中，
这种转移方式称为协同翻译的转移。这是
由于结合到内质网膜的核蛋白体利用蛋白
质合成的能量，迫使其生长的多肽链穿过
内质网膜上由转移器形成的通道。
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跨膜蛋白质的转移
Classify depend on sorting mechanism
Transmembrane transport
 Vesicular transport
 Gated transport指细胞的核、质间蛋白质运输，
通过
核孔复合体来完成
 Cytosol protein sorting
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Protein transmembrane transfer
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Protein transmembrane transfer is more
complex than soluble protein
stop-transfer peptide or halt transfer
peptide locate in middle of peptide ,formed
transmembrane protein
Single transmembrane: only one start
transfer sequence and one stop transfer
sequence
More times transmembrane:more start
transfer sequence and more stop transfer
sequence
跨膜运输
(transmembrane transport)
通过结合在膜上的蛋白质转移器
(protein transportor)穿过膜直接把蛋白
质从细胞质运送到细胞内的不同部位。这
种途径运送的蛋白质必须去折叠(unfold)，
这样，蛋白质更具柔韧性，可蜿蜒穿膜。
如 细胞质中合成后运送到线粒体、叶绿体
中的蛋白质。
5.2.3 Vesicular transport
5.2.3.1Vesicular Type
A Gridding protein coated vesicles网格蛋白有被小泡
B COPⅡ coated vesicles ：ER—Golgi
C COPⅡ coated vesicles
retrieve escaped proteins---ER
A Gridding protein coated vesicles
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Transport protein from TGN golgi to
cytoplasm,lysosome or vacuole
Golgi TGN is origin of gridding protein coated
vesicles
B COPⅡ coated vesicles and regulation
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ER to golgi
COPⅡ coated vesicles select and condense
transfer material
COPⅡ coated vesicles can recognize cytosol
signal of transmembrane ER protein
cavity of transmembrane ER protein
combine with soluble protein of cavity ER
跨膜内质网蛋白的腔面一端作为受体与内质网腔中的
可溶性蛋白（如分泌蛋白）结合
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Sar protein(a small combined GTP protein) ，
can act as molecular switch,regulate vesicular
coat
Sar+GDP=inactive， Sar+GTP=active，Sar
protein combine with membrane of ER，form
COPⅡ coated vesicles
C
COPⅠ coated vesicles
1 Double direction transport
Retrograde transport from Golgi to ER; anterograde
transport from ER to Golgi ;
2 Main function was callback escaped protein from golgi to
ER,
3 Retrieval signal （Lys-asp-glu-leu,or KDEL）, golgi CGN
can recognize retrieval signal,form COPⅠ coated vesicles to
transfort to ER ,If protein was short of retrieval,protein
cannot come back to ER
4 ER is Open prison
Many ER-resident protein
bear a C-Terminal KDEL
Maily located in cis golgi
network and ER-to GOLGI
trasport vesicle
Chief function is bing
proteinwith KDELand
return them to ER
蛋白二硫异构酶和分子“伴
娘”
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内质网驻留蛋白的回收图解
COPⅠvesicle coat regulation
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ARF +GDP=inactive， ARF +GTP=active
ARF change depend on GNRP(鸟嘌呤核苷酸释放蛋
白)and GAP (GTP酶激活蛋白 )
GNRP let ARFrelease GDPand combine with GTP，
ARF becomed active，regulated COPⅠvesicle coat
GAP trigger ARF hydrolyze GTP into GDP， ARF
becomed inactive ， COPⅠ, COPⅠvesicle coat
disaggregation，vesicle fused with target membrane
5.2.3.2 Transport vesicle formation
1 Selective fusion is the key factor for
directional protein trasport.vesicle
from ER only fused with cis CGN(高尔
基体管网区)
2 Rough ER is material source ,and
golgi is important distributing center
3 ER is Open prison
leader peptide
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线粒体、叶绿体中绝大多数蛋白质以及过氧化
物酶体中的蛋白质也是在某种信号序列的指导
下进入这些细胞器中的，这些信号称为导肽或
前导肽，
其基本特征为导肽或前导肽引导蛋白质跨膜过
程中不仅需要ATP使多肽去折叠，而且还需要
一些蛋白质的帮助（如热休克蛋白Hsp70亦
称分子伴娘）使其能够正确地折叠成有功能的
蛋白。
由于这类蛋白质在细胞质基质中合成后再转移
到这些细胞器中，因此称为后转移。
分子“伴娘”
(molecular chaperone)
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通称为结合蛋白(bindin protein,BiP)。
在细胞中这类蛋白能识别正在合成的多肽
或部分折叠的多肽并与多肽的一定部位相
结合，帮助这些多肽的转运、折叠或组装，
但其本身并不参与最终产物的形成，只是
陪伴而已，故得名
例如Hsp60以上的热休克蛋白
分子伴娘是进化上相当保守的一些蛋白
质家族，目前已被确认的有热休克蛋白
Hsp60、70和90等，它们广泛分布于
原核细胞和真核细胞的细胞质、线粒体
和内质网中
5.5.4 Cell assemble system
Self assemble
Aid assemble
Direct assenble
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Cell assemble function
减少和校正蛋白合成中出现的错误
大大减少所需遗传物质信息量
通过装配与去装配更容易调节和控制多种生
物学过程