High-level expression of recombinant protein A in Escherichia coli

A high-level expression plasmid pPA-3 was constructed, which yielded up to 20% of soluble cell proteins as recombinant Protein A in E. coli DH5 alpha strain by heat shock induction. The recombinant Protein A contained only the five domains of native Protein A that bind with the Fc part of IgG. The molecular weights of the recombinant Protein A expressed in E. coli were determined to be 33kDa, 32.2kDa, 29.5kDa and 28.6kDa by SDS-PAGE and Western-blotting. The diversity of the molecular weights may be due to proteolysis, and a possible cleavage site is proposed. Some of the protein was purified with coupled human IgG by one-step affinity chromatography. The reactivity of the protein was compared with that of native Protein A and found that this protein could bind with more IgG than native Protein A in equal quantities of proteins.