Characterization of immunoglobulin G binding to Staphylococcus aureus strain Wood 46.

Protein A (PA)-activity was detected in Staphylococcus aureus strain Wood 46 which had been considered to be PA-negative. This staphylococcal strain bound 28% of 125I-labelled IgG, compared with 89% by strain Cowan I. The binding activities of both S. aureus strains were saturable, time-dependent and specific. The dissociation constants of 1.6 X 10(-9) M for Wood 46 and 9.3 X 10(-8) M for Cowan I indicated a similar affinity for human IgG in both strains. The number of IgG-binding sites were estimated to be 16,970 for Wood 46 and 41,200 for Cowan I. Exposure to heat and ultrasonication reduced PA-activities of strain Cowan I, but not that of strain Wood 46. Extraction of the staphylococci with guanidine and formic acid resulted in a reduction of IgG-binding activities only in strain Wood 46. Photooxidation, trypsinization and lysozyme treatment also diminished IgG-binding of strain Wood 46 to a larger extent than that of strain Cowan I. Extracellular PA from S. aureus strains Wood 46 and Cowan I could be purified by affinity chromatography on IgG-sepharose. The purified PA preparations gave single protein bands upon SDS-polyacrylamide gel electrophoresis. Their molecular weights were 42,000 and their isoelectric points approximated 5.0.