Improving Protein Stability with Amino Acid Polymers during Lyophilization

Proteins are widely used as reagents in laboratories and as therapeutics for a variety of diseases. However, the native proteins are prone to aggregation and can be denatured under extreme conditions such as freezing, drying and dehydration, leading to a reduced activity, and thus an increased dosage. To achieve protein protection under extreme conditions, we prepared two types of amino acid polymers, poly-(L-lysine) (PLL) and poly-L-glutamate (PLG) from the rapid ring-opening polymerization (ROP) of α-amino acid N-carboxyanhydride (NCA) using lithium hexamethyldisilazide (LiHMDS) as the initiator. β-galactosidase (β-Gal) was used as a model protein to examine the protein protective effect of the synthesized amino acid polymers during lyophilization. The results showed that the presence of PLL and PLG blending had significant protection effect on β-Gal activity during lyophilization. The enzyrnatic activity of the lyophilized protein was improved from 38%（without protecting agent）to 77%（with protecting agent）. The results suggest that amino acid polymers are good candidates for protein stabilization under extreme conditions. The easy operation of LiHMDS-initiated, moisture insensitive and rapid NCA polymerization implies great potential of this strategy to prepare simple amino acid polymers for screening of protein stabilization agents.