Expression of Recombinant Proteins in the Methylotrophic Yeast Pichia pastoris

Summary

The protocol describes protein expression using the methylotrophic yeast Pichia pastoris. The preparation of electrocompetent yeast cells, transformation of the vector with the gene of interest into P. pastoris and yeast DNA purification are also performed. Western blot analysis and protein purification build the last steps in this protein expression protocol.

Abstract

Protein expression in the microbial eukaryotic host Pichia pastoris offers the possibility to generate high amounts of recombinant protein in a fast and easy to use expression system.

As a single-celled microorganism P. pastoris is easy to manipulate and grows rapidly on inexpensive media at high cell densities. Being a eukaryote, P. pastoris is able to perform many of the post-translational modifications performed by higher eukaryotic cells and the obtained recombinant proteins undergo protein folding, proteolytic processing, disulfide bond formation and glycosylation [1].

As a methylotrophic yeast P. pastoris is capable of metabolizing methanol as its sole carbon source. The strong promoter for alcohol oxidase, AOX1, is tightly regulated and induced by methanol and it is used for the expression of the gene of interest. Accordingly, the expression of the foreign protein can be induced by adding methanol to the growth medium [2; 3].

Another important advantage is the secretion of the recombinant protein into the growth medium, using a signal sequence to target the foreign protein to the secretory pathway of P. pastoris. With only low levels of endogenous protein secreted to the media by the yeast itself and no added proteins to the media, a heterologous protein builds the majority of the total protein in the medium and facilitates following protein purification steps [3; 4].

The vector used here (pPICZαA) contains the AOX1 promoter for tightly regulated, methanol-induced expression of the gene of interest; the α-factor secretion signal for secretion of the recombinant protein, a Zeocin resistance gene for selection in both E. coli and Pichia and a C-terminal peptide containing the c-myc epitope and a polyhistidine (6xHis) tag for detection and purification of a recombinant protein. We also show western blot analysis of the recombinant protein using the specific Anti-myc-HRP antibody recognizing the c-myc epitope on the parent vector.

Protocol

Expression of recombinant proteins in the methylotrophic yeast Pichia pastoris

Before you start this protocol you should have your gene of interest cloned in frame in a P. pastoris parent vector and have it sequenced to check for the correct insertion of the gene of interest in the vector.

Step I: Generating electrocompetent yeast cells, linearization of the construct and transformation into P. pastoris

For this step you will need to have the following media and plates at hand:

• YPDS plates
• 600 mL YPD medium
• ice-cold ....

Discussion

Protein expression using the methylotrophic yeast Pichia pastoris as a host system is described in this protocol. The protein can be secreted into the medium depending on the used cloning vector. The secretion of the recombinant protein makes the subsequent purification easier. However, the shown conditions may have to be optimized for the expression of different proteins and changes in the conditions and expression times may result in increased protein levels. The vector used in this protocol has the feature of.......