Expression and purification of a truncated recombinant streptococcal protein G

Publisher Website
Google Scholar
Abstract
The gene for Protein G from Streptococcus strain G148 was cloned and expressed in Escherichia coli. The regions on the gene corresponding to the albumin-binding domains and the Fab-binding region were then deleted by site-directed mutagenesis. The translation of regions corresponding to the cell-wall- and membrane-binding domains was prevented by introduction of stop codons upstream of these domains. The recombinant DNA sequence codes for a protein (G'') that contains repetitive regions and that binds only the Fc portion of IgG, analogously to Protein A. Translation of the sequence produces a presence with an Mr of about 20000. The nucleotide sequence differs from those published previously. The protein can be substantially purified on a large scale by chromatography on IgG-Sepharose 4B. Homogeneous Protein G can be prepared by anion-exchange f.p.l.c. on Mono Q HR. This protein G'' has a pI of 4.19 and SDS/PAGE gives an apparent anomalous Mr of 35000.