The present application provides methods and uses of O-oligosaccharyltransferase (O-OTases) for generating vac cines. In particular, the present application provides a method of synthesizing a glycoprotein comprising glycosylation of pilin-like protein ComP using a PglLcomP O-OTase. Uses of glycoproteins synthesized by glycosylating Com P using PglLcomP O-OTase, par ticularly for the preparation of vaccines and the like, including a vaccine to Streptococcus, is also provided.