Purification, crystallization and preliminary X-ray diffraction analysis of RafE, a sugar-binding lipoprotein from Streptococcus pneumoniae

Streptococcus pneumoniae contains a large number of sugar-transport systems and the system responsible for raffinose uptake has recently been identified. The substrate-binding protein component of this system shares strong sequence homology with the multiple sugar metabolism substrate-binding protein MsmE from S. mutans and contains a lipoprotein-attachment site at cysteine residue 23. A truncated form (residues 24-419) of RafE from S. pneumoniae was cloned and overexpressed in Escherichia coli. Native and selenomethionine-labelled protein have been crystallized in the hexagonal space group P6(1)22. Diffraction data have been successfully phased to 2.90 angstroms using Se SAD data and model building is in progress.