I am wondering if "outer membrane protein A" from some bacteria such as E Coli is also a kind of "protein A"? Is "salmonella invasion protein A" also a kind of "protein A"? In addition to Staphylococcus aureus, do other bacteria also produce "protein A"?
E. coli outer membrane protein A (OmpA) is a beta-barrel integral membrane protein. It is not related to the protein A of S. aureus that binds IgG.
Outer membrane Protein A (OmpA) is very different from Staphylococcus aureus Protein A (SPA). The former is an integral membrane protein embedded in the outer membrane of Gram -ve bacterial and is also known as an aquaporin (may also act as an adhesion factor), the latter is a secreted protein that binds to IgG via the Fc region and is part of the bacterial defence against the immune system. Almost all Gram negative bacteria appear to have some analogue of OmpA. SPA, on the other hand, appears to be unique to S. aureus, although other bacteria produce proteins that also bind IgG (e.g. Streptococcal protein G) but are structurally different to SPA.
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