Involved in the polymorphic O-glycosylation of the serine-rich repeat protein PsrP. Catalyzes the third step in glycosylation PsrP in this bacteria. Transfers glucose from UDP-glucose to the terminal glucose moiety of already-glycosylated PsrP (using truncated substrates with PsrP SSR1-GlcNAc-Glc). Has a marked preference for PsrP substrate that has already been modified by GlcNAc and glucose. In vitro has hydrolytic activity against UDP-glucose and to a lesser extent against UDP-galactose. Also catalyzes the fourth step in glycosylation of the serine-rich repeat protein PsrP in this bacteria. Can transfer the sugar from UDP-glucose (and much less well from UDP-galactose) to the terminal sugar moiety of PsrP-GlcNAc-Glc-Gal or of PsrP-GlcNAc-Glc-Glc. Protein modification; protein glycosylation. Encoded in RD10, a pathogenicity island with an atypical GC content that is associated with invasive pneumococcal disease. Pathogenicity islands account for greater than half the genomic diversity observed between isolates (PubMed:11463916, PubMed:16861665). The main function of this island seems to be correct synthesis and export of pneumococcal serine-rich repeat protein PsrP (Probable). Belongs to the glycosyltransferase 2 family.