分子生物学课件蛋白质的翻译后加工

SS
SS
p-Chymotrypsinogen (inactive)
SS
SS
p-Chymotrypsin (inactive)
SS
SS
-Chymotrypsin (active)
Protein Sorting & Targeting
Signal peptide hypothesis (Proposed by GÜNTER BLOBEL -1999 Nobel Laureate in Physiology or Medicine): Proteins have intrinsic signals that govern their transport and localization in the cell. These signals are special aa sequences, which are like the zip codes or address tags. In the absence of signal peptides, a protein will remain in the cytoplasm
N端氨基酸的去除：
共价修饰：
➢ phosphorylation, ➢ acetylation, ➢ methylation, ➢ γ-carboxylation ➢ hydroxylation ➢ glycosylation, ➢ lipidation, ➢ prosthetic group attachment, ➢ disulfide cross-linking,
迄今发现的150多种内蛋白子仅存在于单细胞生物中； 酵母、细菌、病毒等；
a self-catalyzed process
释放出的内蛋白子可以作为核酸内切酶，催化 自身DNA的转移（mobile element）.
多肽链的折叠：
一级结构决定高级结构； 有些蛋白质的折叠需要分子伴侣molecular chaperone
Protein Splicing
Protein splicing is defined as the excision of an intervening sequence (the Intein) from a protein precursor and the concomitant ligation of the flanking protein fragments (the Extein) to form a mature host protein and the free intein
+
3~5 nonconsecutive K or R, often with
S & T, no E & D
+
Generally rich in S & T and small
hydrophobic AAs and poor in E & D
_
Usually SKL
Nucleus
Internal
_
One cluster of 5 basic AAs or two
N-linked oligosaccharide N-terminal
Chloroplast N-terminal
Peroxisome C-terminal
_
KDEL
_
Stop seqeunce
Added in a unique marker in the form of GB mannose-6-phosphate (M6P) groups,
蛋白质的翻译后加工
2006
During translation, about 30-40 polypeptide residues are relatively protected by the ribosome. Once the polypeptide chain emerges from the ribosome it starts to fold and can be subject to post-translational modifications.
Why post-translational processing? 1) adds functionality 2) effects targeting 3) regulates activity 4) changes recognition
Processing types
1) remove of the N terminal AA 2) covalent modification 3) splicing 4) polypeptide chain folding 5) cleavage and trimming
Brings protein to ER
Binds signal sequence on protein
Binds SRP receptor on ER
RNA-protein complex
线粒体蛋白的 定向：
叶绿体蛋白的定向：
细胞核蛋白质 的定向
过氧化物酶体 蛋白的定向
Nature of signal peptide
N-terminal
+
Core of 6~12 hydrophobic AAs often
preceded by one or more basic AAs
ER Transmembrane lysome
Mitochondria
C-terminal C-terminal
2) post-translational targeting: nucleus, mitochondria, chloroplasts, peroxisomes
Target organelle
ER, GB, lysome, plasma membrane, outside cell
Signal location Signal within protein removal
的帮助： 有些蛋白质的折叠需要二硫键异构酶protein disulfide
isomerase (PDI)； 有些蛋白质的折叠需要脯氨酰顺反异构酶peptide prolyl
cis-trans isomerase (PPI)；
多肽链的剪切：
Βιβλιοθήκη Baidu同一前体剪切产生多个蛋白质； 非活性前体剪切产生有活性的成熟蛋白；
蛋白质的定向与分拣：
在核糖体上新合成的多肽被送到细胞的各个部分，行 使各自的生物功能，这个转移和定位的过程称为蛋白 质定向与分拣。
Two Pathways
1) co-translational targeting :ER, Golgi, lysosomes, plasma membrane, secreted proteins
smaller cluster of basic AAs separated
by ~10 AAs
ER信号肽：
一般长约10-20个氨基酸； 主要由疏水性氨基酸残基组成； N端有一个碱性氨基酸； C端有一个极性氨基酸或丙氨酸；
Signal recognition particle (SRP)