Staphylococcus AG structure?
After puzzling over this for a while I think I have the answer . It's nothing to do with protein A or protein G. I think that whoever wrote your study materials meant Ag which is a common abbreviation for 'antigen'. I guess this was in the context of immune responses, or strain typing.

Looking back over your last few questions, it seems that you are at the mercy of a teacher who specialises in ambiguity.