lecture_6-regulation of protein synthesis at the translational level
TRANSCRIPT
-
7/29/2019 Lecture_6-Regulation of Protein Synthesis at the Translational Level
1/12
egulation of Protein Synthesis (6.1)
Lecture 6
Regulation of Protein Synthesis at the Translational Level
Comparison of EF-Tu-GDP and EF-Tu-GTP conformations
EF-Tu-GDP EF-Tu-GTP
Next: Comparison of GDP and GTP binding region in EF-Tu
ase report typos, errors etc. byEMAIL (mention the title of this page).
tp://bass.bio.uci.edu/~hudel/bs99a/lecture25/index.html5/25/2007 9:39:44 AM
mailto:[email protected]:[email protected] -
7/29/2019 Lecture_6-Regulation of Protein Synthesis at the Translational Level
2/12
Regulation of Protein Synthesis (6.1a)
Comparison of GDP and GTP binding region of EF-T
ttp://bass.bio.uci.edu/~hudel/bs99a/lecture25/lecture6_1a.html (1 of 2)5/25/2007 9:39:45 AM
-
7/29/2019 Lecture_6-Regulation of Protein Synthesis at the Translational Level
3/12
Regulation of Protein Synthesis (6.1a)
Next: Molecular Mimicry
ease report typos, errors etc. byEMAIL (mention the title of this page).
ttp://bass.bio.uci.edu/~hudel/bs99a/lecture25/lecture6_1a.html (2 of 2)5/25/2007 9:39:45 AM
mailto:[email protected]:[email protected] -
7/29/2019 Lecture_6-Regulation of Protein Synthesis at the Translational Level
4/12
egulation of Protein Synthesis (6.1b)
Molecular mimicry betweenEF-G and EF-Tu-GTP-aminoacyl-tRNA
EF-G EF-Tu-GTP-Aminoacyl-tRNA
Next: Rates and Energetics of Translation
ase report typos, errors etc. byEMAIL (mention the title of this page).
tp://bass.bio.uci.edu/~hudel/bs99a/lecture25/lecture6_1b.html5/25/2007 9:39:46 AM
mailto:[email protected]:[email protected] -
7/29/2019 Lecture_6-Regulation of Protein Synthesis at the Translational Level
5/12
Regulation of Protein Synthesis (6.2)
Rates and energetics of translation
At 37 C, the rate of translation inE. coli is about 15 amino acids
per second.
The translational rate is equivalent to the transcriptional rate which
is ~45 nucleotides per second.
nergy cost for synthesis of a protein with N amino acids:
2N ATPs to charge tRNA (ATP -> AMP + PP -> AMP + 2Pi)
1 GTP for initiation (IF2)
N-1 GTPs to position tRNA for N-1 peptide bonds (EF-Tu)
N-1 GTPs for N-1 translocation steps (EF-G)
1 GTP for termination (RF-3)
===
4N
Total of 4 high-energy phosphate bonds cleaved per amino acid
ach ATP or GTP cleavage generates ~40 kJ/mol
ach peptide bond costs ~160 kJ/mol in the cell, yet an uncatalyzed chemical
action to form a peptide bond costs only ~20 kJ/mol.
ttp://bass.bio.uci.edu/~hudel/bs99a/lecture25/lecture6_2.html (1 of 7)5/25/2007 9:39:47 AM
http://bass.bio.uci.edu/~hudel/bs99a/lecture21/lecture2_3.htmlhttp://bass.bio.uci.edu/~hudel/bs99a/lecture21/lecture2_3.htmlhttp://bass.bio.uci.edu/~hudel/bs99a/lecture21/lecture2_3.htmlhttp://bass.bio.uci.edu/~hudel/bs99a/lecture23/lecture4_4.htmlhttp://bass.bio.uci.edu/~hudel/bs99a/lecture24/lecture5_3.htmlhttp://bass.bio.uci.edu/~hudel/bs99a/lecture24/lecture5_3.htmlhttp://bass.bio.uci.edu/~hudel/bs99a/lecture24/lecture5_5.htmlhttp://bass.bio.uci.edu/~hudel/bs99a/lecture24/lecture5_5.htmlhttp://bass.bio.uci.edu/~hudel/bs99a/lecture24/lecture5_5.htmlhttp://bass.bio.uci.edu/~hudel/bs99a/lecture24/lecture5_3.htmlhttp://bass.bio.uci.edu/~hudel/bs99a/lecture24/lecture5_3.htmlhttp://bass.bio.uci.edu/~hudel/bs99a/lecture23/lecture4_4.htmlhttp://bass.bio.uci.edu/~hudel/bs99a/lecture21/lecture2_3.html -
7/29/2019 Lecture_6-Regulation of Protein Synthesis at the Translational Level
6/12
Regulation of Protein Synthesis (6.2)
Why is it so costly to make a peptide bond on a ribosome?
The excess energy is used for generating an accurate, defined
polypeptide sequence, not a random one or a combination of
multiple possibilities.
wo sources of errors during translation:
q Attachment of an incorrect amino acid to a tRNA
q Mispairing of the tRNA anticodon with the mRNA codon
wo proofreading mechanisms exist to prevent these errors:
q Proofreading before aminoacyl adenylate intermediate is attached to tRN
q Kinetic proofreading before peptide bond formation: A delay is introduc
between the binding of an aminoacyl-tRNA to the codon and the formatio
of the peptide bond to allow errors to be corrected:
r EF-Tu-GTP binds an aminoacyl-tRNA and bring it into the A-site.
r EF-Tu allows the anticodon to interact with the codon but prevents
peptide bond formation.r An incorrect tRNA will bind weakly to the codon and will dissociate
from the codon before an incorrect amino acid is incorporated into t
polypeptide.
r Correct codon-anticodon matching triggers hydrolysis of GTP by th
EF-Tu, after which EF-Tu-GDP dissociates.
r Peptide bond formation proceeds.
ttp://bass.bio.uci.edu/~hudel/bs99a/lecture25/lecture6_2.html (2 of 7)5/25/2007 9:39:47 AM
http://bass.bio.uci.edu/~hudel/bs99a/lecture21/trna_charge2.gifhttp://bass.bio.uci.edu/~hudel/bs99a/lecture21/trna_charge2.gifhttp://bass.bio.uci.edu/~hudel/bs99a/lecture21/trna_charge2.gifhttp://bass.bio.uci.edu/~hudel/bs99a/lecture21/trna_charge2.gif -
7/29/2019 Lecture_6-Regulation of Protein Synthesis at the Translational Level
7/12
Regulation of Protein Synthesis (6.2)
Each major step in protein synthesis, except peptide-bond
formation itself, involves hydrolysis of GTP to GDP.
Regulation of protein synthesis
ROKARYOTES
Short-lived mRNA (few minutes), so little need for complicated
translational regulation. In prokaryotes, most of the regulation is at the
transcriptional level.
Rates vary only by a factor of 100. Variance is due to differences in ShinDalgarno sequences and how strongly a particular sequence base-pairs w
the 16S rRNA of the 30S ribosomal subunit.
UKARYOTES
Long-lived mRNA (hours to days) and thus a greater need to
regulate the rate of protein synthesis.
ttp://bass.bio.uci.edu/~hudel/bs99a/lecture25/lecture6_2.html (3 of 7)5/25/2007 9:39:47 AM
http://bass.bio.uci.edu/~hudel/bs99a/lecture23/lecture4_3.htmlhttp://bass.bio.uci.edu/~hudel/bs99a/lecture23/lecture4_3.htmlhttp://bass.bio.uci.edu/~hudel/bs99a/lecture23/lecture4_3.htmlhttp://bass.bio.uci.edu/~hudel/bs99a/lecture23/lecture4_3.html -
7/29/2019 Lecture_6-Regulation of Protein Synthesis at the Translational Level
8/12
Regulation of Protein Synthesis (6.2)
Several known mechanisms:
q mRNA masking: mRNA is bound to a variety of proteins that prevent
association with ribosomes. When appropriate signal is received, theproteins dissociate from mRNA, leaving the transcript free to associate w
the ribosome. The signal is usually in the form of phosphorylation/
dephosphorylation. mRNA masking is a major form of regulation in earl
embryonic development.
q antisense RNA: short segment of RNA, complementary to mRNA, that
forms double stranded RNA which cannot be translated by ribosome. Tw
known examples:
r blockage of protein synthesis of fruit-ripening enzyme in tomatoes
r the c-myb gene product which promotes smooth muscle developmen
and blockage in injured arteries.
q Heme Control of Globin Synthesis: Red blood cells are programmed to
synthesize large amounts of globin. The globin chains, subsequent to
translation, are assembled with heme into hemoglobin. If there is an
insufficient supply of heme to insert into the newly synthesized globinchains, then translation is turned off. The lack of heme triggers the
accumulation of a heme-controlled inhibitor (HCI) protein. This protein
a kinase which phosphorylates eIF2-GTP. The phosphorylation blocks th
dissociation of eIF2 and eIF2-beta that normally occurs in the initiation
cycle. Thus, the cell becomes rapidly depleted of unphosphorylated eIF2
which is normally recycled for initiation of additonal mRNA. Either the
ttp://bass.bio.uci.edu/~hudel/bs99a/lecture25/lecture6_2.html (4 of 7)5/25/2007 9:39:47 AM
http://bass.bio.uci.edu/~hudel/bs99a/lecture23/lecture4_5.htmlhttp://bass.bio.uci.edu/~hudel/bs99a/lecture23/lecture4_5.html -
7/29/2019 Lecture_6-Regulation of Protein Synthesis at the Translational Level
9/12
Regulation of Protein Synthesis (6.2)
addition of heme, which represses the production of HCI, or the addition
lots of unphosphorylated eIF2, which bypasses the HCI effect, can restart
initiation again.
q Interferon: Interferons are glycoproteins that are secreted by virus-
infected cells. Interferons prevent additional infection by other types of
viruses by inhibiting protein synthesis in infected cells.
Two mechanisms of action:
r induces production of protein kinase, DAI (double-stranded RNA-
activated inhibitor) which in the presence of dsRNA, phosphorylate
eIF2-alpha and stabilizes the eIF2-alpha-eIF2-beta complex in a
manner similar to the heme-controlled inhibitor (HCI).
r induces a cascade effect which ultimately activates an endonuclease
RNase L, that rapidly degrades mRNA.
Inhibition of protein synthesis by antibiotics
ttp://bass.bio.uci.edu/~hudel/bs99a/lecture25/lecture6_2.html (5 of 7)5/25/2007 9:39:47 AM
-
7/29/2019 Lecture_6-Regulation of Protein Synthesis at the Translational Level
10/12
Regulation of Protein Synthesis (6.2)
ntibiotics are bacterially or fungally produced substances that inhibit the
rowth of other organisms. Antibiotics target a wide spectrum of vital
rocesses: they block DNA replication, transcription and bacterial cell wall
ynthesis. A large number of antibiotics, including medically useful substance
lock protein translation.
locking protein translation is very effective for two reasons:
q Protein translation plays a central role in overall metabolism
q The structural differences between prokaryotic and eukaroytic ribosomes
and associated factors (IFs/EFs/RFs) allow specific targeting.
ttp://bass.bio.uci.edu/~hudel/bs99a/lecture25/lecture6_2.html (6 of 7)5/25/2007 9:39:47 AM
-
7/29/2019 Lecture_6-Regulation of Protein Synthesis at the Translational Level
11/12
Regulation of Protein Synthesis (6.2)
rokaryotic Inhibitors
q Chloramphenicol - inhibits peptidyl transferase on 50S subunit.
q Erythromycin - inhibits translocation by 50S subunit.
q Fusidic acid - inhibits translocation by preventing the dissociation of EF-
GDP from ribosome.
q Puromycin - an aminoacyl-tRNA analog that causes premature chain
termination.
q Streptomycin - causes mRNA misreading and inhibits chain initiation.
q Tetracycline - inhibits binding of aminoacyl-tRNA to ribosomal A-site.
ukaryotic Inhibitors
q Puromycin & Tetracycline (see prokaryotes above).
q Cycloheximide - inhibits peptidyl transferase on 60S subunit.
q Diphtheria Toxin - inactivates eEF-2 by ADP ribosylation.
Summary
ease report typos, errors etc. byEMAIL (mention the title of this page).
ttp://bass.bio.uci.edu/~hudel/bs99a/lecture25/lecture6_2.html (7 of 7)5/25/2007 9:39:47 AM
http://www.doe-mbi.ucla.edu/people/steere/dt_research.htmlhttp://www.urmc.rochester.edu/smd/mbi/bactox/DT.htmmailto:[email protected]:[email protected]://www.urmc.rochester.edu/smd/mbi/bactox/DT.htmhttp://www.doe-mbi.ucla.edu/people/steere/dt_research.html -
7/29/2019 Lecture_6-Regulation of Protein Synthesis at the Translational Level
12/12
ummary (6.3)
Summary
q GTP-binding often causes major conformational changes in
proteins
q Each major step in protein synthesis, except peptide-bond
formation itself, involves hydrolysis of GTP to GDP.
q Four high-energy phosphate-bonds are required for each amino
acid added
q The rate of protein synthesis is well matched to the rate of
transcription
q EF-G is shaped like EF-Tu-GTP-aminoacyl-tRNA (molecular
mimicry)
q mRNA in prokaryotes is short-lived (minutes)q mRNA in eukaryotes is long-lived (hours/days), requiring
additional control
q A large number of antibiotics inhibit protein synthesis, many
specifically in prokaryotes
Next lecture: Post-Translational Processing
ease report typos, errors etc. byEMAIL (mention the title of this page).
http://bass.bio.uci.edu/~hudel/bs99a/lecture26/index.htmlmailto:[email protected]:[email protected]://bass.bio.uci.edu/~hudel/bs99a/lecture26/index.html