Efficient recombinant protein secretion in Mycobacterium smegmatis: A valuable platform for protein production involved in biomedical development targeting mycobacterial diseases

Mycobacterium smegmatis is often used as a host for preparing various recombinant mycobacterial proteins that are used for structural and functional studies. The advantages of M. smegmatis as a host are that it is fast-growing, non-pathogenic, easy to manipulate, and has similar post-translational modifications to other mycobacteria. It is critical to express recombinant proteins with similar conformations and/or functions to native proteins from major pathogenic mycobacterial strains, including both Mycobacterium tuberculosis and non-tuberculosis mycobacteria. Accordingly, M. smegmatis has been chosen as a model for both systems. Therefore, the M. smegmatis expression platform must be applicable not only for functional studies but also for studies of antigen production. In this study, we examined whether the secretion system of M. smegmatis was suitable for establishing a vector capable of producing large amounts of recombinant protein. To do so, we examined the secretions of several mycobacterial secretory proteins in M. smegmatis to identify an effective signal sequence for efficient production. We found that a signal peptide from the Mycobacterium kansasii homolog of Rv1926c demonstrated efficient secretion of targeted mycobacterial proteins. Next, mutant signal peptide analysis revealed that the length of the hydrophobic amino acid stretch region plays a critical factor during signal peptide function. Overall, our data show that the secretion system of M. smegmatis may have potential for production of various mycobacterial proteins for vaccine development and diagnostic research.