The molecule and its structure

A floppy 43-residue chain that grips actin

Thymosin beta-4 has no stable shape in solution. Free in water, its chain of 43 amino acids is predominantly unstructured, the kind of chain called intrinsically disordered, with at most six residues forming a helix, and a few more residues become helical when it binds its best-studied partner, actin. The LKKTET motif in the middle is known as its actin-binding region.

This unit walks the sequence, the disorder, and how the whole peptide wraps an actin monomer, plus what separates trial-grade thymosin beta-4 from a gray-market TB-500 vial.