Affinity purification of recombinant proteins using a LysM domain and bacterium like particles

Abstract

The lysin motif (LysM) is a ubiquitous motif across kingdoms, which in bacteria allows cell wall degrading enzymes to bind noncovalently to peptidoglycan. This property has been exploited for two decades to design mucosal vaccines consisting of LysM-tagged recombinant proteins anchored to bacterium like particles (BLP) as carriers. Surprisingly, less attention has been paid to apply the LysM motif to protein purification of recombinant proteins. Thus, our goal was to determine if the LysM motif is suitable for recombinant protein purification. We obtained the BLPs by treating overnight cultures of lactobacilli with acid and heat to get rid of other cell wall components that may interfere with binding. To select the best binding matrix, we generated BLPs from 3 different Lactobacillus species: L. rhamnosus, L. fermentum, and L. vaginalis and checked them by transmission electron microscopy. We constructed a fusion protein consisting of the yellow fluorescent protein Venus fused to a module containing five LysM motifs derived from a Lactobacillus sp. strain. The recombinant protein was expressed in E. coli Rossetta using standard procedures, and the supernatant containing the fusion protein was incubated with BLPs for binding. We evaluated the effectiveness of binding by fluorescent microscopy and SDS-PAGE. After binding, the complex was washed several times, and the elution of the protein was tested by changing pH, ionic strength and buffer composition. As a conclusion, we demonstrate that the LysM motif can be used as novel tag to purify recombinant proteins by affinity using an economical matrix, obtaining similar yields to the NiNTA system for protein purification.