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Protein structural plasticity exemplified by insertion and deletion mutants in T4 lysozyme
I R Vetter1, W A Baase, D W Heinz
1Institute of Molecular Biology, Howard Hughes Medical Institute, University of Oregon, Eugene 97403, USA.
Protein Science : a Publication of the Protein Society
|December 1, 1996
Summary
Protein structure is adaptable, with alpha-helices often preserving their integrity by shifting residues to accommodate insertions or deletions. This structural plasticity influences protein evolution.
Area of Science:
- Biochemistry
- Structural Biology
- Protein Engineering
Background:
- Proteins are essential biological macromolecules with complex three-dimensional structures.
- Alpha-helices are common secondary structure elements crucial for protein folding and function.
- Understanding how proteins respond to alterations in polypeptide chain length is key to protein engineering and evolutionary studies.
Purpose of the Study:
- To investigate the structural and stability consequences of altering alpha-helix length in T4 lysozyme.
- To elucidate the mechanisms by which proteins accommodate insertions and deletions within helical regions.
- To explore the relationship between structural adaptability and protein evolution.
Main Methods:
- Introduction of 32 insertions and 5 deletions into nine alpha-helices of T4 lysozyme.
- Analysis of protein stability using thermodynamic measurements (kcal/mol).
- Determination of protein structures using X-ray crystallography for wild-type and mutant proteins.
Main Results:
- Insertions and deletions caused varying degrees of protein destabilization, ranging from 1 to 6 kcal/mol.
- Proteins predominantly preserved alpha-helix integrity through residue translocation ('register shift'), often forming loops or bends at helix ends.
- In extreme cases, disruption of the hydrophobic core or 'looping-out' within the helix occurred, leading to substantial destabilization.
Conclusions:
- T4 lysozyme exhibits significant structural plasticity, accommodating polypeptide chain length variations.
- Residue translocation is a primary mechanism for maintaining alpha-helix structure, with varying stability costs.
- The observed structural adaptability provides insights into protein evolution and the potential for engineering novel protein structures.