Immunological applications of type III Fc binding proteins. Comparison of different sources of protein G

Use of protein chip mass spectrometry to monitor biotinylation reactions

Surface-enhanced laser desorption/ionization time-of-flight analysis was used to monitor both the kinetics and heterogeneity of product formation during the biotinylation of a number of model proteins and peptide targets. The selected molecules were the IgG-binding protein, protein A, human serum albumin, and a synthetic peptide corresponding to the N terminus of a streptococcal M1 protein. The extent of biotinylation was determined by kinetic analysis of the shift in molecular mass from the native material. Each residue modified by reaction with N-hydroxysuccinimide biotin resulted in an addition of approximately 341 amu to the native protein or polypeptide. The novelty of the method was in the ability to determine the molecular mass shift, without first separating the targeted molecule from the biotinylating reagent. The analysis was rapid, simple, and provided information on the average number of biotin molecules added and the homogeneity of the resulting product.

Purification of goat immunoglobulin G1 (IgG1) and IgG2 antibodies by use of Streptococcus dysgalactiae cells with Fc receptors

The application of stabilised streptococcal cells for the purification of both immunoglobulin 1 (IgG1) and IgG2 subclasses from goat sera was evaluated. Guanidinium chloride extracted, lyophilised cells of the Lancefield Group C Streptococcus dysgalactiae Sc1 strain showed strong binding to goat IgG, reaching a capacity of approximately 1.4 mg IgG per 100 mg cells (dry weight). The IgG preparation obtained was of high quality. In immunoelectrophoretic analysis the preparation appeared to consist of pure IgG, whereas the high pressure liquid chromatography (HPLC) gel filtration and immunoblot analyses showed a very slight contamination (less than 1.3% of the total probe) with alpha 2-macroglobulin. The presence of both IgG subclasses in the preparation was verified by HPLC ion exchange chromatography. The adsorption procedure proved to be efficient and easy to perform without advanced technical equipment and the cells were reusable. As these streptococcal cells bind both IgG subclasses, this method presents an economical way for the small scale purification of goat IgG. Additionally the streptococcal cells may conveniently substitute Protein A bearing Staphylococcus aureus cells in various immunological assays.

A simple preparative procedure to extract and purify protein G from group G streptococci

A rapid method for the solubilization of the bacterial type III Fc binding protein, protein G, from a group G streptococcus is described. Treatment of intact bacteria with cyanogen bromide results in the solubilization of a homogeneous Mr approximately 50,000 protein which retains IgG and human serum albumin binding properties. The solubilized protein could be purified to homogeneity by molecular sieving chromatography and retained all of the functional properties of the native protein.

Isolated DNA repeat region from fcrA76, the Fc-binding protein gene from an M-type 76 strain of group A streptococci, encodes a protein with Fc-binding activity

The DNA repeat region of fcrA76, the gene encoding a group A streptococcal Fc-binding protein, was subcloned in-frame into an Escherichia coli plasmid expression vector. The expressed protein product displayed the same Fc-binding properties as the full-length Fc-binding protein expressed from fcrA76. The affinity-purified, full-length Fc-binding protein was found to compete with staphylococcal protein A or streptococcal protein G for binding to beads coated with human IgG. These results are consistent with earlier studies suggesting that the binding sites on human IgG for protein A, protein G and the type II Fc-binding protein from group A streptococci are located at the interface of the CH2 and CH3 domains of the Fc region.