Expression and purification of the crystalline surface layer protein of Rickettsia typhi

The crystalline surface layer (S-layer) protein (SLP) of Rickettsia typhi is known as the protective antigen against murine typhus. We previously reported a cloning and sequence analysis of the SLP gene of R. typhi (slpT) and showed that the open reading frame of this gene encodes both the SLP and a 32-kDa protein. To express only the SLP from this gene, the putative signal sequence and the 32-kDa protein portion were removed from the slpT. This protein was expressed in Escherichia coli as a fusion protein, consisting of the SLP and maltose binding protein. The recombinant protein reacted strongly with polyclonal antiserum of a patient with murine typhus.