The Ramachandran Number: An Order Parameter for Protein Geometry.

Area of Science:

• Biophysics
• Materials Science
• Structural Biology

Background:

• Protein structures feature local order (secondary structures like α-helices, β-sheets) defined by dihedral angles (ϕ, ψ).
• Ramachandran plots visualize these angles, typically showing distinct regions for known secondary structures.
• Peptoid nanomaterials exhibit unique secondary structures occupying two Ramachandran plot regions, necessitating new descriptive methods.

Purpose of the Study:

• Introduce a novel 'Ramachandran number' for compactly describing regions on the Ramachandran plot.
• Develop a method to characterize 'higher-order' secondary structures, including those found in peptoids.
• Provide a versatile tool for analyzing protein geometry and structural patterns.

Main Methods:

• Defined a structurally meaningful combination of dihedral angles ϕ and ψ into a single Ramachandran number.
• Applied the Ramachandran number to characterize secondary structure motifs in proteins and peptoids.
• Utilized the Ramachandran number for visualizing structural data in large protein datasets.

Main Results:

• The Ramachandran number effectively describes geometric content of protein structures.
• Diagrams generated using the Ramachandran number reveal frequencies of secondary structures and disordered regions at a glance.
• Demonstrated the utility of the Ramachandran number for analyzing peptoid secondary structures.

Conclusions:

• The Ramachandran number offers a compact and informative descriptor for protein secondary structure.
• This new parameter facilitates rapid analysis and visualization of protein structural data.
• The Ramachandran number shows potential as an order parameter for diverse protein geometry applications.