This thesis reports the viability of E. coli cell extracts prepared using equipment that is both common to biotechnology laboratories and able to process small volume samples and expression of proteins containing unnatural amino acids (UAAs) at higher level using PCR amplified linear DNA templates (LETs) in cell-free protein synthesis (CFPS) system. E. coli-based cell extracts are a vital component of inexpensive and high-yielding CFPS reactions. However, effective preparation of E. coli cell extract is limited to high-pressure homogenizers (French press style or impinge-style) or bead mill homogenizers, which all require a significant capital investment. This work specifically assessed the following capital cost lysis techniques: (1) sonication, (2) bead vortex mixing, (3) freeze-thaw cycling, and (4) lysozyme incubation to prepare E. coli cell extract for CFPS. In this work, simple shake flask fermentation with a commercially available E. coli strain was used. Additionally, the RNA polymerase was over expressed in the E. coli cells prior to lysis which eliminated the need to add independently purified RNA polymerase to the CFPS reaction. As a result, high yielding E. coli-based cell extract was prepared using equipment requiring reduced capital investment and common to biotechnology laboratories. To our knowledge, this is the first successful prokaryote-based CFPS reaction to be carried out with extract prepared by sonication or bead vortex mixing. LETs are an attractive alternative to plasmids for site-specific incorporation of unnatural amino acids in proteins in the CFPS system because of their short preparation time and ease of production. However, major limitations associated with LETs are: (1) their degradation by RecBCD enzyme present in the cell-extract used for CFPS and (2) high CFPS energy costs. In this work, we report the optimization of LET-based CFPS for improved protein yield by inhibiting the RecBCD enzyme with small inhibitor molecules resulting in three fold increment in yield of protein containing UAA. We also assessed alternative energy sources such as glucose, fructose-1,6-bisphospate, creatine phosphate/creatine kinase, and high glutamate salt for cost reduction. This work could be important for high-throughput applications based on linear expression templates. This work demonstrates simple E. coli extract preparation and improved yield with linear expression templates for further advancements of cell-free protein synthesis system.
College and Department
Ira A. Fulton College of Engineering and Technology; Chemical Engineering
BYU ScholarsArchive Citation
Shrestha, Prashanta, "Streamlined Extract Preparation for E. coli-Based Cell-Free Protein Synthesis and Rapid Site-Specific Incorporation of Unnatural Amino Acids in Proteins" (2012). Theses and Dissertations. 3917.
Prashanta Shrestha, cell-free protein synthesis, in vitro protein synthesis, unnatural amino acids, para-proparglyoxyphenylalanine (pPa), cell lysis, cell extract, bead milling, sonication, RecBCD, exonucleases, small molecules, linear expression templates, linear DNA, PCR, transcription, translation