Abstract: The present disclosure includes catalytically active truncations of a protein, referred to as a PnSPase protein, that degrade the capsular polysaccharide of serotype 3 Streptococcus pneumoniae. The disclosure includes a genetically modified cell that includes a PnSPase protein of the present disclosure, and compositions that include the protein, the polynucleotide encoding the protein, the genetically modified cell, or a combination thereof. Also provided are methods for using a PnSPase protein of the present disclosure, including methods for contacting a S. pneumoniae having a type III capsular polysaccharide with a PnSPase protein, increasing deposition of at least one complement component on the surface of a S. pneumoniae, treating an infection in a subject, treating a symptom in a subject, decreasing colonization of a subject by S. pneumoniae, or a combination thereof.