An amino acid code for irregular and mixed protein packing

Area of Science:

• Protein structure and bioinformatics
• Computational biology and biophysics

Background:

• Understanding protein tertiary structure is crucial for molecular biology.
• Existing models often simplify the complex packing of secondary structures.

Purpose of the Study:

• To develop and apply the knob-socket model for analyzing protein tertiary structure.
• To investigate packing patterns in irregular coil, turn, and mixed secondary structures.

Main Methods:

• Development of the knob-socket model based on three-residue sockets (secondary) and four-residue knob-sockets (tertiary).
• Analysis of amino acid composition preferences in sockets and knobs within different secondary structures.
• Identification of canonical packing patterns and crossing angles in beta-sheets and mixed structures.

Main Results:

• The knob-socket model reveals correlations between amino acid composition and tertiary arrangements in coil and turn structures.
• Coil structures contribute significantly to tertiary packing, comparable to alpha-helices.
• Specific amino acid preferences were identified for irregular sockets and knobs, with some amino acids disfavored.
• Mixed packing showed knob preferences dependent on socket type, but not vice-versa.
• A unique coil knob-beta-sheet socket motif may inhibit beta-sheet extension.
• Canonical packing patterns in beta-sheets and mixed structures were identified.

Conclusions:

• The knob-socket model provides an intuitive map of protein tertiary structure topology.
• The model simplifies the complexity of protein packing, aiding in understanding structure-function relationships.
• Identified packing patterns and motifs can inform protein design and engineering efforts.