Use of gram-positive bacteria to express recombinant proteins

Abstract

A novel system for cloning and expression of genes in gram-positive bacteria. The expression system is based on the finding that many gram-positive bacteria sort proteins to their cell surface through cis-acting N-terminal signal sequences and C-terminal anchor regions. In particular, the cell sorting signals of the streptococcal M6 protein, a well-known surface molecule, are used to construct a gram-positive expression system, designated SPEX (Streptococcal Protein Expression). Expression is achieved by cloning the gene of interest into an appropriate SPEX cassette which is then stably introduced into a bacterial host, such as the human commensal Streptococcus gordonii. Depending on the SPEX vector used, recombinant proteins can be anchored to the cell wall prior to release by specific endoproteolytic cleavage or secreted into the culture medium during bacterial growth. The use of host bacteria lacking extracellular proteases should protect secreted proteins from proteolytic degradation. Several expression vectors in this system also produce specifically-tagged recombinant proteins which allows for a one-step purification of the resulting product.