title: A Fab-Selective Immunoglobulin-Binding Domain from Streptococcal Protein G with Improved Half-Life Extension Properties.
abstract: BACKGROUND
  Half-life extension strategies have gained increasing interest to improve the pharmacokinetic and pharmacodynamic properties of protein therapeutics. Recently, we established an immunoglobulin-binding domain (IgBD) from streptococcal protein G (SpGC3) as module for half-life extension. SpGC3 is capable of binding to the Fc region as well as the CH1 domain of Fab arms under neutral and acidic conditions.
  
  
  RESULTS
  Using site-directed mutagenesis, we generated a Fab-selective mutant (SpGC3Fab) to avoid possible interference with the FcRn-mediated recycling process and improved its affinity for mouse and human IgG by site-directed mutagenesis and phage display selections. In mice, this affinity-improved mutant (SpGC3FabRR) conferred prolonged plasma half-lives compared with SpGC3Fab when fused to small recombinant antibody fragments, such as single-chain Fv (scFv) and bispecific single-chain diabody (scDb). Hence, the SpGC3FabRR domain seems to be a suitable fusion partner for the half-life extension of small recombinant therapeutics.
  
  
  CONCLUSIONS
  The half-life extension properties of SpGC3 can be retained by restricting binding to the Fab fragment of serum immunoglobulins and can be improved by increasing binding activity. The modified SpGC3 module should be suitable to extend the half-life of therapeutic proteins and, thus to improve therapeutic activity.
authors.affiliation: Institute of Cell Biology and Immunology, University of Stuttgart, Stuttgart, Germany.
authors.forename: Felix
authors.initials: F
authors.lastname: Unverdorben
authors.affiliation: Institute of Cell Biology and Immunology, University of Stuttgart, Stuttgart, Germany.
authors.forename: Meike
authors.initials: M
authors.lastname: Hutt
authors.affiliation: Institute of Cell Biology and Immunology, University of Stuttgart, Stuttgart, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Seifert
authors.affiliation: Institute of Cell Biology and Immunology, University of Stuttgart, Stuttgart, Germany.
authors.forename: Roland E
authors.initials: RE
authors.lastname: Kontermann
mesh_terms: D000595:Amino Acid Sequence; D000915:Antibody Affinity; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics; D001665:Binding Sites; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D006207:Half-Life; D007136:Immunoglobulins / Q000378:metabolism*; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; C034284:IgG Fc-binding protein, Streptococcus; D007136:Immunoglobulins