Engineering streptococcal protein G for increased alkaline stability.
Most protein-based affinity chromatography media are very sensitive towards alkaline treatment, which is a preferred method for regeneration and removal of contaminants from the purification devices in industrial applications. In a previous study, we concluded that a simple and straightforward strategy consisting of replacing asparagine residues could improve the stability towards alkaline conditions. In this study, we have shown the potential of this rationale by stabilizing an IgG-binding domain of streptococcal protein G, i.e. the C2 domain. In order to analyze the contribution of the different amino acids to the alkaline sensitivity of the domain we used a single point mutation strategy. Amino acids known to be susceptible towards high pH, asparagine and glutamine, were substituted for less-alkali-susceptible residues. In addition, aspartic acid residues were mutated to evaluate if the stability could be further increased. The stability of the different C2 variants was subsequently analyzed by exposing them to NaOH. The obtained results reveal that the most sensitive amino acid towards alkaline conditions in the structure of C2 is Asn36. The double mutant, C2(N7,36A), was found to be the most stable mutant constructed. In addition to the increased alkaline stability and also very important for potential use as an affinity ligand, this mutated variant also retains the secondary structure, as well as the affinity to the Fc fragment of IgG.
Gülich
Susanne
S
Department of Biotechnology, Royal Institute of Technology (KTH), Stockholm Centre for Physics, Astronomy and Biotechnology (SCFAB), SE-106 91 Stockholm.
Linhult
Martin
M
Ståhl
Stefan
S
Hober
Sophia
S
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001216:Asparagine / Q000737:chemistry / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics* / Q000276:immunology; D002846:Chromatography, Affinity; D002942:Circular Dichroism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007141:Immunoglobulin Fc Fragments / Q000737:chemistry / Q000276:immunology; D007525:Isoelectric Focusing; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011489:Protein Denaturation; D015202:Protein Engineering / Q000379:methods; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012972:Sodium Hydroxide / Q000737:chemistry
D001426:Bacterial Proteins; C034284:IgG Fc-binding protein, Streptococcus; D007141:Immunoglobulin Fc Fragments; D012972:Sodium Hydroxide; D001216:Asparagine