A crystallizable form of the Streptococcus gordonii surface antigen SspB C-domain obtained by limited proteolysis.

SspB is a 1500-residue adhesin expressed on the surface of the oral bacterium Streptococcus gordonii. Its interaction with other bacteria and host cells initiates the development of dental plaque. The full-length C-terminal domain of SspB was cloned, overexpressed in Escherichia coli and purified. However, the protein could not be crystallized. Limited proteolysis of the full-length C-domain identified a core fragment. The proteolysis product was cloned, expressed and purified. The protein was crystallized using the hanging-drop vapour-diffusion method. X-ray data were collected and processed to a maximum resolution of 2.1 A with 96.4% completeness. The crystals belonged to space group P2(1), with one molecule in the asymmetric unit, a solvent content of 33.7% and a corresponding Matthews coefficient of 1.85 A(3) Da(-1).