Cooperative multivalency converts disorder into rods, resolving a paradox in cellular architecture

Area of Science:

• Cell Biology
• Structural Biology
• Biochemistry

Background:

• KANK1 organizes microtubules at focal adhesions via a long, intrinsically disordered linker (L2).
• The mechanism by which L2 spans the membrane-microtubule gap (35-50 nm) remains unclear.

Purpose of the Study:

• To elucidate how the KANK1 L2 linker spans the membrane-microtubule gap.
• To investigate the role of the hub protein LC8 in organizing KANK1.

Main Methods:

• In-cell, biochemical, and biophysical assays.
• AlphaFold predictions for motif interaction and multivalent assembly.
• Electron microscopy for structural analysis.

Main Results:

• LC8 converts the intrinsically disordered KANK1 L2 into an elongated, multivalent, rod-like assembly.
• Physiologically relevant concentrations show LC8 binding arises from cooperativity among multiple weak sites, not isolated motifs.
• LC8 acts as a molecular switch, rigidifying and extending KANK1 L2.

Conclusions:

• LC8 forms compositionally homogeneous yet conformationally adaptable rods that bridge the membrane-microtubule gap.
• This interaction expands the LC8 binding repertoire and reveals design principles for multivalent protein assembly.
• A generalizable strategy for tuning protein architecture length, rigidity, and flexibility is suggested.