Several strategies to
Bsend^ heterologous proteins to the cell surface of LAB
strains or into the environment have been developed. For antigen
secretion, the signal sequence of the protein Usp45 (unknown
secreted protein of 45 kDa)—the only L. lactis protein
secreted in significant quantities by L. lactis—is generally
used (van Asseldonk et al. 1990). The Usp45 signal sequence
also led to satisfactory secretion in Lactobacillus species