The gram-positive bacterium Lactococcus lactis is a useful host for extracellular protein production. A main advantage of L. lactis over other bacterial expression systems is that lactococcal cells display low levels of autolysis and proteolysis. Previously， we developed a set of vectors for nisin-inducible extracellular production of N- or C-terminally hexa-histidine (His)-tagged proteins. The present study was aimed at expanding our portfolio of L. lactis expression vectors for protein purification and site-specific labeling. Specifically， we present two new groups of vectors allowing N- or C-terminal provision of proteins with a Strep-tag II or AVI-tag. Vectors for AVI-tagging encode an additional His-ta... More
The gram-positive bacterium Lactococcus lactis is a useful host for extracellular protein production. A main advantage of L. lactis over other bacterial expression systems is that lactococcal cells display low levels of autolysis and proteolysis. Previously， we developed a set of vectors for nisin-inducible extracellular production of N- or C-terminally hexa-histidine (His)-tagged proteins. The present study was aimed at expanding our portfolio of L. lactis expression vectors for protein purification and site-specific labeling. Specifically， we present two new groups of vectors allowing N- or C-terminal provision of proteins with a Strep-tag II or AVI-tag. Vectors for AVI-tagging encode an additional His-tag for protein purification. Another set of vectors allows removal of N-terminal Strep- or His-tags from expressed proteins with the tobacco etch virus protease. Two possible applications of the developed vectors are presented. First， we show that Strep-tagged LytM of Staphylococcus aureus in the growth medium of L. lactis can be directly bound to microtiter plates coated with an affinity reagent and used for enzyme-linked immunosorbent assays. Second， we show that the AVI-tagged Sle1 protein from S. aureus produced in L. lactis can be directly biotinylated and fluorescently labeled. The fluorescently labeled Sle1 was successfully applied for S. aureus re-binding studies， allowing subcellular localization by fluorescence microscopy. In conclusion， we have developed a set of expression vectors that enhances the versatility of L. lactis as a system for production of proteins with tags that can be used for affinity purification and site-specific protein labeling.
