Protein Expression and Libraries Facility

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Baculovirus expression systems
Lentivirus preparation
Vector DB
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Baculovirus expression systems

DNA Transfection for Baculovirus Expression Vector System 
Spodoptera frugiperda (Sf9) insect cells are cotransfected with the transfer vector (donor or shuttle) plasmid DNA containing the foreign gene to be expressed and BaculoGold™ DNA (PharMingen), Bac-N-Blue™ DNA (Invitrogen), or BacPAK6™ DNA (Clontech).  Alternatively, insect cells are
transfected with a recombinant bacmid DNA constructed by transposition of the donor plasmid DNA in E. coli cells, the so-called Bac-to-Bac™ (Invitrogen-Gibco/Life Technologies) method. The baculovirus DNA is from Autographica californicanuclear polyhedrosis virus (AcNPV). The
BaculoGold™ and Bac-to-Bac™ methods are designed to achieve virtually 100% recombination efficiencies and recombinant protein expression is subsequently evaluated using recombinant virus amplified (without plaque purification) in P2 in insect cells. A single plaque purification of recombinant
virus from the initial virus production (P1 virus) is optional before virus is amplified in a second passage (P2) or higher. Recombinant baculovirus derived from all other commercially available baculovirus DNA preparations is produced with 80-90% efficiency and requires plaque purification to remove parental virus. 

Recombinant Baculovirus Stocks
High titer P2 virus stock is produced from the P1 virus (the original virus from cell culture supernatant of co-transfected cells) in Sf9 cells.  P2 virus stock is generally produced in 100 ml of serum-free medium.  A P3 virus (50 ml or 500 ml) is produced by infecting Sf9 cells with a P2 virus at a low multiplicity of infection (MOI=0.1).

Plaque Assay and Purification of Recombinant Baculovirus
Plaque assays are done by infecting sf9 or sf21 insect cells with the P1 virus (or higher passage virus) at a low multiplicity of infection (MOI = 0.1) and overlaying the infected cells with agarose.  Well isolated plaques are scored and virus is subsequently amplified in monolayer cultures of Sf9 cells prior to preparation of larger volume high-titer stocks.

Time-Course Study of Protein Expression 
100 ml suspension cultures of insect cells are infected with a high-titer baculovirus stock at an MOI=1-2.  Cells or conditioned media (for secreted proteins) are harvested at 24, 48, and 72 hours post infection to evaluate the integrity, stability and optimum yield of the product(s) of gene expression. The results can be used to determine optimal conditions for protein production.. Harvested samples are analyzed for expression of the recombinant protein by western blot.  The staff can compare recombinant protein production in at least three different cell lines (sf9, sf21, and High Five) if necessary.

Large-Scale Production of Recombinant Proteins 
High density (1-2 x106 cells/ml) suspension cultures of Sf9, Sf21, or Trichoplusia ni (commonly referred to as High Five) cells are infected at a multiplicity of infection (MOI) equal to 1-2. High Five cells are preferred for production of secreted proteins. We routinely infect cultures (250 ml to 1 L) of insect cells in serum-free medium containing Pluronic F-68 (to prevent cell damage due to shearing) in spinner bottles.
For additional information about insect cell culturing and baculovirus expression systems, please see:
          Guide to baculovirus expression systems and insect cell culturing (PDF)
          Bac-to-Bac Baculovirus expression systems (PDF)
          Baculodirect Baculovirus Expression Systems (PDF)
          Baculovirus Expression Vector Systems (PDF)
          Bac-N-Blue Baculovirus Expression System (PDF)

Lentivirus preparation

HIV-derived lentiviral vectors have been developed as a gene delivery system that can mediate the efficient delivery, integration, and sustained long-term expression of transgenes to dividing and non-dividing cells in vitro and in vivo. Over the years, lentiviral vectors have turned out to represent very powerful tools in basic and translational scientific research. As such, the facility has implemented the infrastructure and technology to produce high-titer lentiviral vectors. In addition, we have pursued their technological improvement for constitutive and conditional expression of cDNAs and shRNAs.

Lentivirus particles are generated by co-expressing the virion packaging elements and the vector genome 
via transient transfection in a producer cell line (e.g. HEK293T). For HIV-1-based vectors, the core and enzymatic components of the virion come from HIV-1, 
while the envelope is derived from a heterologous virus, most often vesicular stomatitis virus (VSV) 
due to the high stability and broad tropism of its G protein. 
By convention, the former elements are referred to as the LV packaging system and the latter as the envelope.

3 components are required to produce an infectious lentivirus vector
• vector, e.g. pLU, pLKO, pGIPZ
• packaging system, e.g. pCMV-dR8.91, psPAX2 (2nd generation)
• envelope plasmid, e.g. pMD2G (VSVg)

Three generations of HIV-based LV packaging systems have been
developed for production of lentivectors by transient transfection.

The first generation LV packaging system encompasses all HIV-1 genes besides the envelope.

The second generation LV packaging system is additionally deleted in all viral auxilliary genes, 
i.e. vpr, vif, vpu and nef. Examples: pCMV-dR8.91, pCMV-dR8.74, psPAX2

The third generation LV packaging system comprises only gag, coding for the virion main structural proteins and pol, responsible for the retrovirus-specific enzymes. A cDNA encoding rev, which encodes a post-transcriptional regulator necessary for efficient gag and pol expression, is provided on a separate plasmid. The third generation packaging system offers maximal biosafety but is more cumbersome, involving the transfection of four different plasmids in the producer cells.
Plasmid DNAs for the 3rd generation packaging system include pMDL g/p RRE and pRSV-Rev.

All lentiviral vectors that contain a wild-type 5'LTR (e.g. pGIPZ) need to be packaged with a 2nd generation packaging system, as wt 5'LTR requires TAT for maximal activation of transcription. The 3rd generation packaging system can only be used with a lentiviral vector with a chimeric 5'LTR e.g. CCL-, RRL-, etc, in which HIV promoter has been replaced with CMV or RSV, thus making them TAT-independent. The lentivectors carrying the chimeric 5'LTR can be packaged into both, 2nd or 3rd generation packaging system.

The production of vector particles by our facility uses a second generation packaging system, which satisfies most applications.

The vector itself is the only genetic material transferred to the target cells. It typically comprises the transgene cassette flanked by cis-acting elements necessary for its encapsidation, reverse transcription and integration. As previously done with oncoretroviral vectors, advantage was taken of the gymnastics of reverse transcription to engineer self-inactivating (SIN) HIV-1-derived vectors, which lose the transcriptional capacity of the viral long terminal repeat (LTR) once transferred to target cells. This minimizes the risk of emergence of replication 
competent recombinants (RCR) and avoids problems linked to promoter interference.

Vector DB (Note this site is under construction.  Links to maps and sequences are incomplete)

Bacterial Expression Plasmids

Baculovirus Expression Vectors

Mammalian Expression Vectors

Lentivirus vectors