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Exploring the functional robustness of an enzyme by in vitro evolution
M A Martinez1, V Pezo, P Marlière
1Unité de Rétrovirologie Moléculaire, Institut Pasteur, Paris, France.
The EMBO Journal
|March 15, 1996
Summary
In vitro protein evolution using RNA hypermutagenesis accelerates enzyme development. This method generated active dihydrofolate reductase variants with over 20% amino acid changes, surpassing natural evolutionary rates.
Area of Science:
- Biochemistry
- Molecular Biology
- Protein Engineering
Background:
- Natural protein evolution proceeds through gradual accumulation of mutations.
- In vitro methods aim to expedite protein evolution for research and applications.
- RNA hypermutagenesis is a technique to increase mutation rates during in vitro evolution.
Purpose of the Study:
- To accelerate the evolution of active enzymes using RNA hypermutagenesis.
- To generate diverse mutant lineages of Escherichia coli dihydrofolate reductase (DHFR).
- To investigate the role of specific protein regions in enzyme robustness and mutational tolerance.
Main Methods:
- Iterative RNA hypermutagenesis applied to the R67 plasmid-encoded DHFR gene.
- cDNA synthesis using biased deoxynucleotide triphosphate (dNTP) concentrations to induce mutations.
- Deletion and substitution of the N-terminal 22 residues to assess functional impact.
Main Results:
- Generated active DHFR enzyme variants with over 20% amino acid replacement.
- Identified the N-terminal 22 residues as a determinant of R67 DHFR robustness.
- Demonstrated that complete substitution of the N-terminus still permitted further mutation fixation.
Conclusions:
- RNA hypermutagenesis is an effective tool for rapid in vitro protein evolution.
- The N-terminus of R67 DHFR plays a crucial role in enzyme stability and tolerance to mutations.
- This approach enables the creation of novel active proteins from existing genes via a pathway distinct from natural selection.