STRUCTURAL-PROPERTIES OF THE MYELIN-ASSOCIATED GLYCOPROTEIN ECTODOMAIN

Myelin-associated glycoprotein (MAG) has been proposed to mediate adhe sive interactions during myelin development. We have used the baculovi rus expression system to produce a truncated form of this molecule [so luble extracellular domain of MAG (sMAG)] consisting of the complete e xtracellular ectodomain. Spectroscopic studies indicate a high beta-sh eet content, consistent with the prediction of Ig-like structure. Hydr odynamic studies indicate an asymmetric monomer, with a Stokes radius of 4.1-4.6 nm, a sedimentation coefficient of 3.6S, and a frictional r atio of approximately 1.6. We postulate that the outer two Ig-like dom ains form a unit that folds back over the rest of the molecule. Fluore scence quenching studies indicate that sMAG interacts with divalent ca tions and may have a functional lectin domain.