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3(10)-helices in proteins are parahelices
Purevjav Enkhbayar1, Kunio Hikichi, Mitsuru Osaki
1Division of Biological Resources and Production, Graduate School of Agriculture, Hokkaido University, Sapporo, Hokkaido 060-8589, Japan.
Proteins
|June 20, 2006
Summary
The 3(10)-helix, a common protein structure, becomes less stable and more irregular as it lengthens. Longer 3(10)-helices are better described as parahelices due to inherent instability.
Area of Science:
- Biochemistry
- Structural Biology
- Computational Biology
Background:
- The 3(10)-helix is a secondary structure motif in proteins defined by specific hydrogen bonding patterns.
- Understanding the stability and geometric parameters of 3(10)-helices is crucial for protein structure prediction and analysis.
Purpose of the Study:
- To analyze the structural and energetic properties of 3(10)-helices of varying lengths.
- To determine if a uniform definition based on average dihedral angles is appropriate for 3(10)-helices.
- To investigate the stability of regular 3(10)-helices and their prevalence in proteins.
Main Methods:
- Utilized the HELFIT program to determine helical parameters like pitch, radius, and root mean square deviation (rmsd).
- Classified 3(10)-helices as regular or irregular based on rmsd values.
- Performed energy minimizations to assess the stability of different helix lengths.
Main Results:
- Systematic shifts in backbone dihedral angles (phi, psi) were observed across helix positions and lengths.
- Regular 3(10)-helices become thinner and longer with increasing length (N=5-8), but their fraction decreases linearly.
- All helices longer than N=9 were found to be irregular, and stability decreases with length.
Conclusions:
- The definition of 3(10)-helices using average dihedral angles is inappropriate due to position-specific variations.
- Extended, regular 3(10)-helices are inherently unstable in polypeptides.
- Observed 3(10)-helices in proteins are more accurately termed parahelices.
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