The core protein of 294 amino acids has an extracellular domain of 235 amino acids and a single transmembrane domain of 25 amino acids. The extracellular domain has up to three heparan sulphate and two chondroitin or dermatan sulphate chains plus an N linked oligosaccharide.
The heparan sulphate chains bind to several proteins of the extracellular matrix, including collagens, fibronectin and tenascin. The cytoplasmic domain is thought to interact with actin filaments. Its name is derived from the greek syndein, to bind together.