Disorder in cholesterol-binding functionality of CRAC peptides: a molecular dynamics study.

Area of Science:

• Biochemistry and Molecular Biology
• Structural Biology
• Membrane Biophysics

Background:

• The cholesterol recognition/interaction amino acid consensus (CRAC) motif is key for identifying cholesterol-binding regions in proteins.
• Leukotoxin A (LtxA), a bacterial toxin, possesses two CRAC sequences, with only one mediating essential cholesterol binding for cytotoxicity.
• The precise factors governing CRAC motif functionality and its atomic interactions with cholesterol remain incompletely understood.

Purpose of the Study:

• To elucidate the structural characteristics and specific interactions of LtxA CRAC peptides with cholesterol-containing and cholesterol-devoid lipid bilayers.
• To identify the molecular determinants of cholesterol-binding functionality within the LtxA CRAC motif.

Main Methods:

• Utilized molecular dynamics simulations to analyze the behavior of two LtxA CRAC peptides.
• Investigated peptide interactions with both pure phospholipid and binary cholesterol-phospholipid bilayers.

Main Results:

• Observed significant changes in peptide secondary structure upon cholesterol binding, absent in cholesterol-devoid membranes.
• Identified a crucial role for the central tyrosine residue within the CRAC motif in cholesterol binding.
• Demonstrated that residues outside the canonical CRAC motif also influence membrane interactions and LtxA functionality.

Conclusions:

• Cholesterol binding induces specific structural alterations in LtxA CRAC peptides, linking structural disorder to functional outcomes.
• The central tyrosine residue is critical for LtxA's cholesterol interaction, highlighting its importance beyond the basic CRAC definition.
• A comprehensive understanding of LtxA's membrane interaction requires considering both CRAC motif residues and flanking amino acids.