Compositions and methods for preventing and treating pneumococcal infections are provided. Compositions include novel polypeptides comprising an amino acid sequence corresponding to the R21 or R22 domain of CbpA or a consensus sequence of one of these domains, and variants and fragments thereof, wherein the polypeptide is stabilized in a desired conformation, particularly a loop conformation. The polypeptides of the invention may be engineered to comprise a first and a second cysteine residue, thereby resulting in the formation of a disulfide bond that stabilizes the polypeptide in the desired conformation. Alternatively, a polypeptide of the invention may be modified to create a synthetic linkage between a first and second amino acid residue present within the polypeptide, wherein the synthetic linkage stabilizes the polypeptide in the desired conformation. The polypeptides of the invention may further comprise an amino acid sequence for a T cell epitope. Compositions further include isolated nucleic acid molecules that encode the polypeptides of the invention, immunogenic compositions and vaccines comprising the disclosed polypeptides, and antibodies specific for these polypeptides.