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The K. lactis Protein Expression Kit provides an easy method for expressing a gene of interest in the yeast Kluyveromyces lactis. Proteins may be produced intracellularly or secreted using an integrative expression vector (pKLAC2). To achieve protein secretion, a gene of interest is cloned downstream of the K. lactis α-mating factor secretion domain, which is eventually processed in the Golgi and results in secretion of the desired protein.
Supplied with competent K. lactis cells (NEB# C1001)
Allows cloning and expression of genes toxic to E. coli
Rapid high cell density growth results in high yield protein expression
Easy-to-use protocols for those inexperienced with yeast systems
The K. lactis Expression Kit provides an easy method for expressing a gene of interest in the yeast Kluyveromyces lactis (Figure 1). Proteins may be produced intracellularly or be secreted using the supplied integrative expression vector pKLAC2 (Figure 3). To achieve protein secretion, a gene of interest is cloned downstream of the K. lactis α-mating factor secretion domain (α-MF; Figure 4) which is eventually processed in the Golgi resulting in secretion of the desired protein (Figure 1).
The K. lactis expression system offers several advantages over other yeast and bacterial protein expression systems. First, K. lactis has been used to produce proteins at industrial scale in the food industry for over a decade due to its ability to rapidly achieve high culture densities and abundantly produce recombinant proteins (Figure 2). Second, yeast expression is driven by a variant of the strong LAC4 promoter that has been modified to lack background expression in E. coli (1). Therefore, genes toxic to E. coli can be cloned into pKLAC2 in bacteria prior to their expression in yeast. Third, the kit includes highly competent K. lactis cells making the technology easy-to-use for those not accustomed to working with yeast. Their high transformation efficiency makes the system suitable for methods that require large numbers of transformants, for example, expression cloning using cDNA libraries. Selection of yeast transformants uses a unique antibiotic-free method in which acetamidase (amdS) expressed from pKLAC2 permits transformed cells to utilize acetamide as a sole nitrogen source on defined medium. Acetamide selection promotes formation of cells containing multiple integrations of pKLAC2 which results in higher yields of protein. Finally, proteins expressed in K. lactis have access to eukaryotic protein folding and glycosylation machinery that E. coli cells do not possess, making it an important alternative to bacterial expression systems.
Figure 1:
Secreted protein processing. In the nucleus, an integrated expression vector encoding a fusion between the α-MF domain (blue) and a desired protein (black) is expressed. A signal peptide in the α-MF domain directs entry of the fusion protein into the endoplasmic reticulum (ER) and is removed by signal peptidase (SP). The fusion protein is transported to the Golgi where the Kex protease removes the α-MF domain. The protein of interest is then secreted from the cell.
Figure 2:
SDS-polyacrylamide gel electrophoresis separation of secreted recombinant maltose binding protein (MBP) and detection by Coomassie staining. Lane 1: Protein Molecular Weight Markers. Lane 2: spent culture medium (15 µl) from wild-type K. lactis cells. Lane 3: spent culture medium (15 µl) from K. lactis cells harboring an integrated expression cassette containing the E. coli malE gene.
Figure 3: The pKLAC2 expression vector. pKLAC2 (9107 bp) contains the 5´ and 3´ ends of the LAC4 promoter (PLAC4-PBI) separated by DNA encoding β-lactamase (ApR) and the pMB1 origin (ori) to allow for its propagation in E. coli. The K. lactis α-mating factor secretion leader sequence (α-MF), multiple cloning site (MCS), and the LAC4 transcription terminator (TT) lie immediately downstream of 3´ PLAC4-PBI. The yeast ADH1 promoter (PADH1) drives expression of an acetamidase selectable marker gene (amdS). The vector can be linearized by digestion with SacII or BstXI to create a linear DNA fragment capable of inserting into the native LAC4 promoter region of the K. lactis genome.
Figure 4: pKLAC2 (9107 bp) contains the K. lactis a-mating factor secretion leader sequence (blue background) and a polylinker immediately downstream of the PLAC4-PBI promoter. Unique polylinker restriction sites are indicated. Arrows indicate the positions of pKLAC-series vector-specific sequencing primers that you can have synthesized to confirm your target gene is properly cloned.
Highlights
Kit Components
The following reagents are supplied with this product:
NEB 5-alpha Competent E. coli (High Efficiency) (NEB #C2987), NEB 5-alpha Electrocompetent E. coli (NEB #C2989) and NEB 5-alpha Competent E. coli (Subcloning Efficiency) (NEB #C2988) are all recommended for propagation and subcloning pKLAC1 control plasmid and pKLAC2 vector.
NEBuilder HiFi DNA Assembly Cloning Kit (NEB #E5520) or the Gibson Assembly Cloning Kit (NEB #E5510) are excellent ways to assemble a linear yeast expression cassette. (See "Improved method for assembly of linear yeast expression cassettes using NEBuilder® HiFi DNA Assembly Master Mix" in the Application Notes section under the Other Tools and Resources tab)
Quality Control tests are performed on each new lot of NEB product to meet the specifications designated for it. Specifications and individual lot data from the tests that are performed for this particular product can be found and downloaded on the Product Specification Sheet, Certificate of Analysis, data card or product manual. Further information regarding NEB product quality can be found here.
The Specification sheet is a document that includes the storage temperature, shelf life and the specifications designated for the product. The following file naming structure is used to name these document files: [Product Number]_[Size]_[Version]
The Certificate of Analysis (COA) is a signed document that includes the storage temperature, expiration date and quality controls for an individual lot. The following file naming structure is used to name these document files: [Product Number]_[Size]_[Version]_[Lot Number]
This product is covered by one or more patents, trademarks and/or copyrights owned or controlled by New England Biolabs, Inc (NEB).
While NEB develops and validates its products for various applications, the use of this product may require the buyer to obtain additional third party intellectual property rights for certain applications.
For more information about commercial rights, please contact NEB's Global Business Development team at gbd@neb.com.
This product is intended for research purposes only. This product is not intended to be used for therapeutic or diagnostic purposes in humans or animals.
New England Biolabs (NEB) is committed to practicing ethical science – we believe it is our job as researchers to ask the important questions that when answered will help preserve our quality of life and the world that we live in. However, this research should always be done in safe and ethical manner. Learn more.
Licenses
Notice to Buyer/User: The K. lactis Protein Expression Kit was developed from basic research at New England Biolabs, Inc. and DSM Biologics Company B.V. The buyer and user has a non-exclusive sublicense to use this system or any component thereof, including the K. lactis GG799 Competent Cells, for RESEARCH PURPOSES ONLY. A license to use this system for manufacture of clinical grade material or commercial purposes is available from New England Biolabs, Inc., or DSM Biologics Company B.V.
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