A structural entropy index to analyse local conformations in intrinsically disordered proteins

Area of Science:

• Biochemistry
• Structural Biology
• Computational Biology

Background:

• The sequence-structure-function paradigm in proteins has been significantly impacted by the discovery of intrinsically disordered proteins and regions.
• Defining protein flexibility and disorder is complex, often inferred from experimental data like X-ray structures (B-factors, missing residues).
• A precise description of the continuum between rigidity, flexibility, and disorder has been lacking.

Purpose of the Study:

• To precisely describe and quantify the continuum of local dynamics in proteins, ranging from rigidity to flexibility and disorder.
• To introduce and validate an entropy index derived from a structural alphabet for measuring these dynamic states.
• To identify non-disordered regions within intrinsically disordered protein ensembles.

Main Methods:

• Application of a structural alphabet, Protein Blocks, to analyze the local conformation of disordered protein ensembles.
• Development and utilization of an entropy index based on the Protein Blocks structural alphabet.
• Analysis of X-ray structural data to assess residue flexibility (B-factors) and identify missing residues.

Main Results:

• Protein Blocks effectively highlighted rigid local domains within flexible protein regions, discriminating between deformability and mobility.
• The derived entropy index accurately measured local protein dynamics.
• The study quantified, for the first time, the continuum of states from rigidity to flexibility and disorder.
• Non-disordered regions were identified within the studied ensemble of disordered proteins.

Conclusions:

• The Protein Blocks structural alphabet and its associated entropy index provide a powerful tool for characterizing protein dynamics.
• This approach enables a quantitative understanding of the continuum between protein rigidity, flexibility, and disorder.
• The findings contribute to a more nuanced understanding of protein structure-function relationships, particularly for disordered proteins.