Analysis and use of the serum albumin binding domains of streptococcal protein G.
Streptococcal protein G is an IgG-binding receptor with a molecular weight of 63 kDa as predicted from the sequence of the corresponding gene. Here we show that a truncated recombinant protein of 23 kDa still has IgG-binding capacity and also interacts specifically with human serum albumin (HSA). This demonstrates that protein G is a bifunctional receptor. To investigate the structures needed for IgG- and albumin-binding, different parts of the receptor molecule were produced in E. coli using a coupled expression/secretion system. Affinity chromatography, using IgG or HSA immobilized on Sepharose, showed that the two binding activities are structurally separated. From these experiments, it was concluded that a region of 64 amino acid residues is sufficient for albumin-binding. The structure of this part of the protein suggests either a divalent or a trivalent binding capacity. The specific interaction to albumin was used to purify a heterologous protein by affinity chromatography to yield a pure fusion protein in a one-step procedure. The implication of this novel affinity system as a tool to facilitate protein immobilization and purification is discussed.
Nygren
P A
PA
Department of Biochemistry, Royal Institute of Technology, Stockholm, Sweden.
Eliasson
M
M
Abrahmsén
L
L
Uhlén
M
M
Palmcrantz
E
E
D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D002417:Cattle; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D011485:Protein Binding; D011817:Rabbits; D011994:Recombinant Proteins / Q000378:metabolism; D012709:Serum Albumin / Q000378:metabolism*; D013045:Species Specificity; D013329:Structure-Activity Relationship
D001426:Bacterial Proteins; C034284:IgG Fc-binding protein, Streptococcus; D007074:Immunoglobulin G; D011994:Recombinant Proteins; D012709:Serum Albumin