Introduction

There has been a wide array of peptides, either innate or synthetic, used as drugs or vaccine in combat of different diseases. For instance, insulin was synthesized and mass produced in bacteria; long, synthetic peptide vaccine has also brought to bedside to help treat patient with invasive cancers. (Nat Rev Cancer. 2008 May;8(5):351-60.) However, the delivery of the peptide into human body is a big issue, since it cannot be administered orally, and has a poor distribution and absorption as compared to small molecules drugs in human body. With the advent of biotechnology and the growing forum of synthetic biology, we try to engineer and finely design different circuits in bacteria, which can deliver peptides through epidermal, buccal, rectal, or enteral. As for a simple exemplification of our ultimate goal of microbial peptide delivery system, we choose GLP-1, the endogenous hormone as our delivery model. Our design features efficiency, quick response to the environment changes, and sustainable release of GLP-1. This is the first model of our peptide delivery system, and opens a new room for the synthetic biology in medicine applications.

GLP-1, a human innate neuro-peptide for energy balance, is chosen to combat for obesity and metabolic syndrome. We engineer the non-pathogenic E. coli which senses fatty acids in intestines and secretes synthetic GLP-1. Appropriate signal peptides and penetratin are used to facilitate peptide secretion and intestinal uptake. Furthermore, we design a circuit with quorum sensing and double repressors, which aims to generate quick but sustainable responses and serves as an anti-noise filter. Plasmid stabilization modules including partition system and multimer resolution system are also incorporated to circumvent the undesirable loss or segregational instability of our artificial device. With this general concept of delivery of short peptide into human body, we can also target other human diseases with alternative circuit designs.