Production of protein conjugate vaccines by use of transpeptidase enzymes, such as sortase enzymes. For example, homogenous immunoconjugates (e.g., a population of molecules having the same structure) formed by conjugating an antigenic polypeptide and a bacterial capsule component are provided. In certain aspects, methods for generating an immune response to B. anthracis by use of protective antigen-PDGA immunoconjugates are provided.