Properties and characteristics of Staphylococcus aureus A protein

(1)SPA exists in most Staphylococcus aureus, but not in Staphylococcus epidermidis. It mainly exists in plasma coagulase positive strains, but not in negative strains. The former is pathogenic and the latter is non-pathogenic, but no positive correlation between SPA and the pathogenicity of the strain was found in the in vivo study. There are obvious differences in SPA content among different strains. Staphylococcus aureus strain I has the highest SPA content, and SPA binds to peptidoglycan in the cell wall with the valence of * * *. The mutant resistant to dimethoxybenzylpenicillin can produce secretory SPA, and its immunological properties are similar to those contained in cell wall, but it is easy to separate and has less loss. (2)SPA is a component of protein, which contains little or no carbohydrate, and its molecular weight varies with different extraction methods. The cell wall was digested by deoxyribonuclease, ultracentrifugation or hot oil extraction, and the molecular weight was 12000 ~ 15000. After precipitation equilibrium analysis and gel filtration, the molecular weight was 42000. SPA is a polypeptide single chain, which contains three highly similar Fc segment binding regions, each of which is composed of more than 50 amino acids, and contains no tryptophan and cysteine. Its carboxyl terminal is lysine, and its amino terminal structure has not been confirmed. The viscosity of SPA is higher than that of globulin, and its isoelectric point is pH5. 1. Its natural structure is very stable. In the case of using 6mol/L guanine hydrochloride denaturant, some tertiary structures can still be retained. If this denaturant is removed, it can be corrected naturally and the original structure can be restored.

(3) 3) The reason why SPA attracts the attention of immunologists is because of its immunological characteristics. SPA has the ability to bind IgG to humans and many animals such as guinea pigs, pigs, mice and monkeys. The binding site of SPA is Fc segment rather than Fab segment, and this binding will not affect the activity of antibody. The binding force of SPA is bivalent. Each SPA molecule can bind two IgG molecules at the same time, and can also bind IgG on the one hand and fluorescein, peroxidase, colloidal gold, ferritin and other markers on the other. Another interesting fact is that IgG bound to SPA can be dissociated by 4mol/L guanine hydrochloride. SPA is selective in binding IgG immunoglobulin subtypes. For example, SPA has binding ability to human IgG subtypes: IgG 1, IgG2 and IgG4, but does not bind IgG3. Only IgA2 is bound, but IgA 1 is not bound. SPA does not bind to IgG in poultry serum.

(4)SPA has many biological functions, such as inducing the free and contraction of guinea pig ileum, inhibiting the phagocytosis and sterilization of IgG opsonin in phagocytosis, fixing human complement and fresh complement of human, dog and pig, and promoting the mitosis of human B cells.