Signal peptides

How signal peptides work

A signal peptide, also called leader peptide, is the first part of extracellular proteins and can vary in length, its a short sequence fused to the N-terminus of a protein. The ones we work with are 25 amino acids and 50 amino acids in length. The signal peptides enables the protein to be translocated through the bacterial plasma membrane via the SecY complex. [1]

Lactobacillus - A champion of protein secretion

One of the specific advantageous traits of the lactobacillus genus is that they are great at secreting proteins. Therefore we decided to synthesize the signal peptide usp45 from lactococcus lactis according to the Freiburg fusion standard to enable fusion with any protein. This peptide has been shown to work in lactobacillus reuteri together with GFP and will probably work in other lactobacillus species. [2] Our goal is fuse this with a protein called miraculin [3]. This peptide acts as a sweetener by binding to taste receptors on the tongue and gives acidic or sour foods a sweet taste. Since it needs to bind to these receptors it is easier to reap its benefits if it is readily available in the probiotic product rather than contained within the bacteria.

References:

[1] Rapoport T. (Nov. 2007). "Protein translocation across the eukaryotic endoplasmic reticulum and bacterial plasma membranes.". Nature 450 (7170): 663–9. [2] Chi-Ming Wu. (April 2006). “Green fluorescent protein is a reliable reporter for screening signal peptides functional in Lactobacillus reuteri” Journal of Microbiological Methods (2006) 181-186. [3] https://2013.igem.org/Team:Uppsala/miraculin