One of the most significant challenges in biotechnology is technological utilization of self-assembled systems. Surface (S-) layer technology is advanced due to the intrinsic property of subunits to reassemble into two-dimensional arrays. Lactobacillus acidophilus ATCC 4356 composed of S-layer protein (SlpA) subunits which are organized into regular arrays. Herein, S-layer gene (slpA) of L. acidophilus was cloned in Escherichia coli BL21 and recombinant SlpA (rSlpA) expression was verified by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and western-blotting. Temperature of induction (18°C for 18 h), cell density (OD600) 1 and isopropyl β-D-1- thiogalactopyranoside (IPTG) concentration of 0.1 mM were the optimum expression conditions for the rSlpA production with the concentration of 3 mg/ml. Since rSlpA was aggregated as inclusion bodies in the pellet of cell lysis, purification of rSlpA subunits was carried out by the on-column refolding method based on urea gradient. The structural analysis of rSlpA was analyzed by far-UV circular dichroism and transition electron microscope (TEM). The present study suggests production of SlpA in large quantities due to development of biotechnological applications of S-layer nanostructures.

Keywords: Expression, purification, Lactobacillus acidophilus ATCC 4356, optimization, S-layer protein, oncolumn refoldin