Trigger Factor of P. haloplanktis: BBa_K3121000
While researching the literature for bacterial strategies enabling survival under suboptimal conditions (cold temperatures) we came across a remarkable protein which is a key regulator of these adaptive strategies - the Trigger Factor (hereon referred to as TF). As our new part submission to the iGEM Biobrick repository, we have decided to contribute the TF, originally found in Antarctic bacterium Pseudoalteromonas haloplanktis, and codon-optimized it to be expressed in E. coli.
First, let’s take a look at what makes the TF such an essential player under cold conditions. At low temperatures, the usual rate-limiting step for efficient growth is protein folding. In fact, the regular chaperone systems, for instance, the GroEL/ES are also faced with significant challenges at colder conditions, which severely hamper their activity. This leads to a dramatic decrease in bacterial growth and proliferation.
The TF, in essence, is a cold-active chaperone, which is significantly upregulated at low temperatures. This is especially helpful because unlike standard chaperones, the TF has a very unique operational mechanism - it requires near-zero temperatures to stably bind unfolded polypeptides. Under cold conditions, the TF will find almost all the newly synthesized polypeptides, and thereby rescue the chaperone function of the cold-inactivated GroEL/ES (and similar chaperone complexes like the DnaK). Additionally, the TF is a monomeric chaperonic unit, which has considerable structural flexibility in order to compensate for the reduced molecular motions at lower temperatures.
Interestingly enough, the TF is not an essential gene under mesophilic growth conditions - indicating a specialized adaptive role. Moreover, the niche (yet indispensable) requirement of TF is underscored by the fact that the other two major chaperone systems - GroEL/ES and DnaK are significantly downregulated, as well as inactivated, under cold conditions - thereby making the TF system the only chaperone in this scenario.
In light of the above, we realized the vital importance of the TF in enabling stable growth and proliferation of bacteria under cold temperatures, and hence, targeted a new part development endeavor focused on the TF.
