Xin Du, Ewa Marszal, and Andrew Shrake, Laboratory of Plasma Derivatives, Division of Hematology, Office of Blood Research and Review, CBER, FDA
The normal physiological role of alpha-1-proteinase inhibitor (A1-PI) is inhibition of neutrophil elastase. A1-PI, purified from human plasma, is a licensed biologic used to treat patients with mutant A1-PI, which polymerizes and accumulates in hepatocytes thereby reducing circulating levels causing progressive emphysema and, in a substantial portion of these patients, leading to severe liver disease.
Normal A1-PI can be induced to polymerize by partially unfolding it by treatment with a low concentration of denaturant or by heating at GT 37 deg C. Previously, our laboratory demonstrated that fully folded, purified disulfide-linked dimer, formed in 1.4 M guanidine-HCl (Gu) in the absence of reducing agent, spontaneously polymerizes at LT 37 deg C. To investigate the nature of the interactions involved in the formation of dimer and polymerization of it and monomer, we studied the effect of ethylene glycol on the polymerization of: (1) partially purified dimer in buffer at 4 and 25 deg C; (2) monomer in buffer heated at 45 and 60 deg C; and (3) monomer in 1.4 M Gu at 25 deg C.
Results suggest that the formation of the dimeric intermediate from monomeric intermediates involves hydrophobic interactions whereas, in the further polymerization of the dimer and monomer, such interactions may play a less significant role.