Comparison of the PspA sequence from Streptococcus pneumoniae EF5668 to the previously identified PspA sequence from strain Rx1 and ability of PspA from EF5668 to elicit protection against pneumococci of different capsular types.

PspA (pneumococcal surface protein A) is a serologically varied virulence factor of Streptococcus pneumoniae. In mice, PspA has been shown to elicit an antibody response that protects against fatal challenge with encapsulated S. pneumoniae, and the protection-eliciting residues have been mapped to the alpha-helical N-terminal half of the protein. To date, a published DNA sequence for pspA is available only for S. pneumoniae Rx1, a laboratory strain. PspA/EF5668 (EF5668 indicates the strain of origin of the PspA) is serologically distinct from PspA/Rx1. Sequencing of the gene encoding PspA/EF5668 revealed 71% identity with that of PspA/Rx1. The greatest amount of divergence between the two proteins was seen in their alpha-helical portions, which are surface exposed and probably under selective pressure to diversify serologically. In spite of the diversity within the alpha-helical regions of PspAs, we have observed that recombinant PspA (rPspA)/EF5668, like rPspA/Rx1, can elicit cross-protection against pneumococci of different capsular and PspA serological types.