Revision as of 06:17, 22 September 2015

Lpp-OmpA-N

Introduction

Fig.1 Lpp-OmpA-NcoI

Lpp-OmpA protein is the expression system of outer membrane protein, which consists of the 20 amino acids of signal sequence, the nine N-terminal amino acids of the lipoprotein (Lpp) and the residual 46-159 amino acids of the OmpA. The lipoprotein (Lpp) is the most abundant protein on the outer membrane, which possesses the function of targeting to the outer membrane. The OmpA domain constitutes eight-stranded β-barrel to construct an anchor on the outer membrane, providing the stable expression of the protein displayed on the outer membrane. By taking advantage of efficient targeting OmpA to the outer membrane, it allows C-terminal fusion of the protein sequence to be displayed out of the outer mambrane.

Modifying and Improving the Existed Biobrick

To be mentioned, we modified this commonly used transmembrane protein which has been submitted by Warsaw iGEM team in 2008, BBa_K103006 . The most contributed modification to this biobrick is that we replaced the long GS linker behide the transmembrane protein but we chose a six nucleotides restriction site, NcoI, to make it express remarkably on the outer membrane. This change has two benefits. First, the appearance of NcoI allowed the linked protein, for example scFv in our project, to be easily changed and to be brought outside conveniently (like a cassette). Second, NcoI also can act as an useful linker in fusion protein (between transmembrane protein and the linked protein), this has been proved in our project. Moreover, we also selected the amino acids of OmpA from the twenty-fifth one to the one hundred thirty-eighth one to ensure that the displayed linked protein (scFv) can stay closer to the outer membrane and will not swing and move uncontrollably at the outer environment.

The features of Lpp-OmpA expression system

The special restriction site─NcoI： This design avoids the problem of using mixed restriction sites.

The versatile applications： The diversity of introduced protein connecting to OmpA can provide the multiple functions outside the surface of the E. coli. For instance, in our project, we can change every kind of scFv we want.

The stabilization of expression： Due to the anchoring capabilities of lipoprotein and outer membrane protein, the Lpp-OmpA expression system can display passenger proteins more efficiently and also performs the strong adaptability to the various passenger protens.

Experiment

After receiving the DNA sequences from the gene synthesis company, we recombined each Lpp-OmpA-N gene to PSB1C3 backbones and conducted a PCR experiment to check the size of each of the Lpp-OmpA-N. The DNA sequence length of the Lpp-OmpA-N is around 400~500 bp. In this PCR experiment, the Lpp-OmpA-N products size should be near at 650~750 bp. The Fig.2 showed the correct size of the Lpp-OmpA-N, and proved that we successful ligated the Lpp-OmpA-N sequence onto an ideal backbone.

Fig.2 The DNA sequence length of the Lpp-OmpA-N is around 400~550 bp. In this PCR experiment, the Lpp-OmpA-N products size should be close to 650~800 bp.

Fig.3 Lpp-OmpA-NcoI

Sequence and Features