Unusual biophysics of immune signaling-related intrinsically disordered proteins

Area of Science:

• Biophysics
• Molecular Biology
• Cell Signaling

Background:

• Intrinsically disordered (ID) regions are crucial in cell signaling and often found in cytoplasmic segments of plasma membrane proteins.
• Signaling subunits of immune receptors, such as T cell receptor and B cell receptor, contain ID regions within their cytoplasmic domains.
• These domains feature immunoreceptor tyrosine-based activation motifs (ITAMs) critical for signal transduction.

Purpose of the Study:

• To characterize the biophysical properties of intrinsically disordered proteins (IDPs) in immune receptor signaling.
• To investigate novel phenomena associated with these IDPs, including dimerization and membrane interactions.
• To re-evaluate fundamental paradigms in protein biophysics and receptor signaling.

Main Methods:

• Characterization of cytoplasmic domains of immune receptor signaling subunits as intrinsically disordered proteins (IDPs).
• Biophysical studies to analyze dimerization properties (specific, fast/slow equilibrium) and interactions with folded proteins.
• Investigation of dual-mode binding to model membranes with varying lipid bilayer stability.

Main Results:

• Identified cytoplasmic domains of immune receptor signaling subunits as a novel class of IDPs.
• Observed specific dimerization of IDPs, with varied equilibrium kinetics.
• Demonstrated no disorder-to-order transition upon dimerization or interaction with folded partners.
• Revealed dual binding modes to lipid bilayers, dependent on membrane stability.

Conclusions:

• Intrinsically disordered proteins in immune receptor signaling exhibit unique biophysical properties.
• These properties challenge conventional understanding of protein structure-function relationships.
• Findings provide new perspectives on the molecular mechanisms underlying immune receptor signal transduction.