α[sub 1] Acid Glycoprotein: a Small-Angle Neutron Scattering Study of a Human Plasma Glycoprotein.

Small-angle neutron scattering experiments on α₁ acid glycoprotein showed that it has a molecular weight of 37000 and a matchpoint of 44.7% ²H₂O The molecular weight, the matchpoint and a &vmacr; of 0.704 ml/g are in agreement with the primary sequence and standard residue volumes for amino acids and carbohydrates. The radius of gyration R_G of α₁ acid glycoprotein was found to be independent of concentration in the range 2- 11 mg/ml, but increases on going from a buffer containing 0.2 MnaCl to one containing 1 M NaCl. A contrast variation study showed that the R_G at infinite contrast is 2.47 nm fir the expanded form and 2.19 nm for the contracted form, and that the two Stuhrmann α values are similar at 27 x 10^-5. The latter is greater than the expected for globular proteins and are explained by the surface disposition of the five glycan chains on a core of protein in α₁ acid glycoprotein. Modeling calculations account for the two R_G values in which for the expanded form the glycan chains extend out into the solvent and for the contracted form they either fold back or are splayed our such that they are able to interact with surface of the protein core. [ABSTRACT FROM AUTHOR]