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Relocation or duplication of the helix A sequence of T4 lysozyme causes only modest changes in structure but can
Martin Sagermann1, Walter A Baase, Blaine H M Mooers
1Institute of Molecular Biology, Howard Hughes Medical Institute, and Department of Physics, 1229, University of Oregon, Eugene, Oregon 97403-1229, USA.
Biochemistry
|February 6, 2004
Summary
Circularly permuting T4 lysozyme reveals how helix A
Area of Science:
- Protein folding and structural biology
- Biochemistry and molecular biophysics
Background:
- Helix A in T4 lysozyme is N-terminal in sequence but C-terminal in structure.
- This unusual arrangement raises questions about protein folding pathways.
Purpose of the Study:
- To investigate the role of helix A's position in T4 lysozyme folding.
- To explore how structural domain reconstitution is affected by sequence permutation.
Main Methods:
- Creation and structural analysis of a circularly permuted T4 lysozyme variant.
- Engineering a second variant with duplicated helix A sequences.
- Crystallography and stability/folding rate measurements.
Main Results:
- A circularly permuted variant showed helix A can form a contiguous domain.
- This variant exhibited reduced stability but faster folding.
- A duplicated helix A variant showed N-terminal helix A folded normally, C-terminal looped out, leading to slower folding.
Conclusions:
- The spatial arrangement of helix A is crucial for T4 lysozyme stability and folding kinetics.
- Competing identical sequence segments significantly impede protein folding rates.