Protein A isolated from Staphylococcus aureus after digestion with lysostaphin.

Previous methods which have been used for the preparation of protein A, such as thermal release of protein A with lysozyme from the bacteria, have given a heterogenous product in a low yield. The present publication reports the isolation procedure of protein A from Staphylococcus aureus digested by lysostaphin for 2 h at 37°C. 450—500 mg of protein A was obtained from 300 g of wet bacteria. The preparation is homogenous as seen from its disc electrophoretic pattern. Amino acid composition was determined and based on a molecular weight of 42000. The number of amino acid residues found was 378 ± 6. Less than 0.2% hexosamines was present. The ultraviolet spectrum and the absorption coefficient, A1%275nm= 1.65 of protein A is given. Less than 0.1 mol amino terminal amino acid per mol protein was detected which indicates that the protein has a blocked N-terminal amino acid. The protein was slowly digested with a mixture of carboxypeptidase A and B and 2 mol lysine/mol protein was released. Precipitation of protein A with normal human γ-globulin gave an IgG: protein A molar ratio of 2.1:1 within the equivalence zone. The results are discussed with regard to the subunit structure of the protein and the type of attachment of protein A to the peptidoglycan part of the cell wall.