Activity-based in vitro selection of T4 DNA ligase

Progresses in Cell-Free In Vitro Evolution

Biopolymers, such as proteins and RNA, are integral components of living organisms and have evolved through a process of repeated mutation and selection. The technique of "cell-free in vitro evolution" is a powerful experimental approach for developing biopolymers with desired functions and structural properties. Since Spiegelman's pioneering work over 50 years ago, biopolymers with a wide range of functions have been developed using in vitro evolution in cell-free systems. The use of cell-free systems offers several advantages, including the ability to synthesize a wider range of proteins without the limitations imposed by cytotoxicity, and the capacity for higher throughput and larger library sizes than cell-based evolutionary experiments. In this chapter, we provide a comprehensive overview of the progress made in the field of cell-free in vitro evolution by categorizing evolution into directed and undirected. The biopolymers produced by these methods are valuable assets in medicine and industry, and as a means of exploring the potential of biopolymers.

Bacterial Cell Display as a Robust and Versatile Platform for Engineering Low-Affinity Ligands and Enzymes

Directed evolution has been remarkably successful at expanding the chemical and functional boundaries of biology. That progress is heavily dependent on the robustness and flexibility of the available selection platforms, given the significant cost to (re)develop a given platform to target a new desired function. Bacterial cell display has a significant track record as a viable strategy for the engineering of mesophilic enzymes, as enzyme activity can be probed directly and free from interference from the cellular milieu, but its adoption has lagged behind other display-based methods. Herein, we report the development of SNAP as a quantitative reporter for bacterial cell display, which enables fast troubleshooting and the systematic development of the display-based selection platform, thus improving its robustness. In addition, we demonstrate that even weak interactions between displayed proteins and nucleic acids can be harnessed for the specific labelling of bacterial cells, allowing functional characterisation of DNA binding proteins and enzymes, thus making it a highly flexible platform for these biochemical functions. Together, this establishes bacterial display as a robust and flexible platform, ideally suited for the systematic engineering of ligands and enzymes needed for XNA molecular biology.

In vitro evolution of enzymes

In the past decade, in vitro evolution techniques have been used to improve the performance or alter the activity of a number of different enzymes and have generated enzymes de novo. In this review, we provide an overview of the available in vitro methods, their application, and some general considerations for enzyme engineering in vitro. We discuss the advantages of in vitro over in vivo approaches and focus on ribosome display, mRNA display, DNA display technologies, and in vitro compartmentalization (IVC) methods. This review aims to help researchers determine which approach is best suited for their own experimental needs and to highlight that in vitro methods offer a promising route for enzyme engineering.

Selection of mRNA 5'-untranslated region sequence with high translation efficiency through ribosome display

The 5'-untranslated region (5'-UTR) of mRNAs functions as a translation enhancer, promoting translation efficiency. Many in vitro translation systems exhibit a reduced efficiency in protein translation due to decreased translation initiation. The use of a 5'-UTR sequence with high translation efficiency greatly enhances protein production in these systems. In this study, we have developed an in vitro selection system that favors 5'-UTRs with high translation efficiency using a ribosome display technique. A 5'-UTR random library, comprised of 5'-UTRs tagged with a His-tag and Renilla luciferase (R-luc) fusion, were in vitro translated in rabbit reticulocytes. By limiting the translation period, only mRNAs with high translation efficiency were translated. During translation, mRNA, ribosome and translated R-luc with His-tag formed ternary complexes. They were collected with translated His-tag using Ni-particles. Extracted mRNA from ternary complex was amplified using RT-PCR and sequenced. Finally, 5'-UTR with high translation efficiency was obtained from random 5'-UTR library.

Selection strategies for improved biocatalysts

Enzymes have become an attractive alternative to conventional catalysts in numerous industrial processes. However, their properties do not always meet the criteria of the application of interest. Directed evolution is a powerful tool for adopting the characteristics of an enzyme. However, selection of the evolved variants is a critical step, and therefore new strategies to enable selection of the desired enzymatic activity have been developed. This review focuses on these novel strategies for selecting enzymes from large libraries, in particular those that are used in the synthesis of pharmaceutical intermediates and pharmaceuticals.

In vitro selection of zinc finger DNA-binding proteins through ribosome display

DNA-binding proteins with sequence specificities have a variety of applications. To create novel functional DNA-binding proteins, in vivo selection methods have been developed. There are, however, crucial problems with such methods, e.g., limitation of library size and difficulty of expression of toxic proteins for the host cells. In order to overcome these problems, we developed a novel way to select DNA-binding proteins using an in vitro ribosome display technique. The three zinc finger DNA-binding protein libraries, based on a Zif268 containing randomized sequence in each finger, were prepared and transcribed to mRNA in vitro. The ternary ribosomal complexes, formed by mRNA, ribosome, and translated DNA-binding protein during translation in a rabbit reticulocyte in vitro translation system, were selected with biotinylated target DNA fragments bound to streptavidin magnetic beads. The extracted mRNAs from the selected complexes were amplified using reverse transcription PCR and then sequenced. This is the first report of the selection of DNA-binding proteins involving an in vitro ribosome display technique.