The principal investigator has made the observation that a C-terminal deletion mutant of SspB, expressed in E. faecalis, produced a protein that attached to the cell wall like the wild-type protein. This was an unexpected result since the deletion removed three C-terminal domains that are thought to be required for the proper secretion/attachment of Gram positive cell wall proteins. Strong cell attachment of the mutant SspB was inferred in that the protein was not found in the culture supernatant and treatment of the cells with chaotropic and ionic agents as well as SDS did not release the protein from the cell. The surface of E. faecalis cells, expressing the recombinant protein, were labeled with anti-SspB antibody that confirmed that the truncated protein was targeted to the cell wall. Finally, the principal investigator determined that the recombinant protein retained biological activity by demonstrating that the E. faecalis cells, expressing the mutant protein, would aggregate in the presence of salivary agglutinin. These observations suggested that the binding of SspB to the cell surface was not dependent on the 3 C-terminal domains which have been shown to be important for the cell surface attachment of other Gram positive surface proteins. Thus, the SspB protein must use some other signals that are present upstream of the deleted amino acids.
