Novel expression systems for recombinant protein production at low temperatures

One of the main limitations experienced while producing proteins in conventional bacterial mesophilic systems is the need to operate at their optimal growth temperature (usually 37 oC) for the production process. Since temperature has a general negative impact on protein folding due to the strong temperature dependence of hydrophobic interactions that mainly drive the aggregation reaction, the production of recombinant proteins at low temperatures represents an exciting model to improve the quality of the products. Recombinant protein production in psychrophilic bacteria, i.e. at temperature as low as 4°C, may minimise undesired hydrophobic interactions during protein folding, desirably resulting in enhancing the yield of soluble and correctly folded products. In this context, a few cold adapted species are under early but intense exploration as cold cell factories, among them, Pseudoalteromonas haloplanktis being a representative example. The efficiency of cold-adapted expression systems was tested by fully soluble and biologically competent production of several thermal-labile and aggregation-prone products in PhTAC125 such as the mature human nerve growth factor and a yeast αglucosidase Furthermore, with respect to E. coli, PhTAC125 is extremely efficient in secreting proteins in the culture medium. By the use of a psychrophilic α-amylase as secretion carrier for the extra-cellular targeting of recombinant proteins an efficient gene-expression system was set up. Observed efficiency of the cold-adapted system (secretion yield was always above 80%) placed it amongst the best heterologous secretion systems in Gram-negative bacteria reported so far.