Lecture 7
Post-Translational Processing
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Protein synthesis consists of several
steps: from the translation of the information from mRNA to the folded
and fully processed, active protein in its proper compartment of action.
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The mRNA sequence predicts a specific length polypeptide
chain made up of the primary 20 amino acids.
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Fully processed protein products are almost always
shorter than their mRNA would predict, and globally contain about 200 different
amino acids.
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(determined by sequencing, biochemistry, X-ray crystallography)
During translation, about 30-40 polypeptide residues are relatively protected
by the ribosome (tunnel T and exit sites E1 and E2 in the large subunit).
Once the polypeptide chain emerges from the ribosome it starts to fold
and can be subject to post-translational modifications.
So after translation several additional steps must be considered as part
of the complete protein biosynthetic process:
1. Covalent modification of
a: peptide bonds
b: the N-terminus
c: the C-terminus
d: amino acid residues (side chains).
2. Noncovalent modifications: folding, addition of
co-factors.
3. Translocation: compartment selection and transport
(Trafficking/Targeting).
4. Involvement of molecular chaperones in 1, 2,
and 3.
Why post-translational processing?
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adds functionality
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effects targeting
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regulates activity
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increases mechanical strength
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changes recognition
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