Twist and shear in beta-sheets and beta-ribbons.

Area of Science:

• Protein structure analysis
• Structural bioinformatics
• Biophysics

Background:

• Beta-sheets and beta-ribbons are fundamental protein secondary structures.
• Understanding their structural nuances is key to protein folding and function.
• Existing models do not fully explain observed asymmetries like sheet twist and strand shear.

Purpose of the Study:

• To analyze the structural asymmetries in parallel and antiparallel beta-sheets and beta-ribbons.
• To identify the interactions and correlations responsible for these asymmetries.
• To develop a model that explains the origin of sheet twist and strand shear.

Main Methods:

• Analysis of high-resolution protein structure data.
• Systematic measurement of sheet twist and strand shear.
• Examination of residue interactions, correlations, and hydrogen bonding patterns.
• Utilizing Ramachandran plot analysis for residue conformations.

Main Results:

• Strongest correlations for asymmetries found in non-hydrogen-bonded pairs in antiparallel beta-sheets/ribbons.
• Identified a bifurcated hydrogen bond linking neighboring beta-strands.
• Ramachandran plot regions for beta-structures are influenced by bifurcated H-bonds and steric interactions.
• A model successfully reproduced shear and twist using bifurcated H-bonds and Ramachandran plot parameters.

Conclusions:

• Bifurcated hydrogen bonds are crucial for linking beta-strands and influencing structure.
• Specific residue interactions and steric factors dictate the distinct conformations in beta-sheets and beta-ribbons.
• The study provides a mechanistic understanding of beta-structure formation and asymmetry.