%0 Journal Article
%T In Vitro Selection of Fab Fragments by mRNA Display and Gene-Linking Emulsion PCR
%A Takeshi Sumida
%A Hiroshi Yanagawa
%A Nobuhide Doi
%J Journal of Nucleic Acids
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/371379
%X In vitro selection by display methods has been an effective tool for engineering recombinant antibodies. mRNA display based on a cell-free translation system has the advantages of larger library sizes and quicker selection procedures compared with cell-based display methods such as phage display. However, mRNA display has been limited to select single-chain polypeptides such as scFvs due to its characteristic of linking a nascent polypeptide with its encoding mRNA on the ribosome. Here we demonstrated a new way of selecting heterodimeric Fab fragments by using mRNA display combined with emulsion PCR. We designed a pair of complementary 5กไ UTR sequences that can link the Fab heavy and light chain genes together by overlap-extension PCR in water-in-oil emulsions. We confirmed that two mRNA-displayed polypeptides for heavy and light chain of a model Fab fragment were associated into the active form and that a specific Fab fragment gene was enriched over 100-fold per round of a model affinity selection followed by the gene-linking emulsion PCR. We further performed directed evolution of Fab fragments with higher binding activity from a randomized Fab fragment library. 1. Introduction In vitro selection by display methods has been an effective tool in the field of protein engineering and especially has been used to engineer recombinant antibodies for various biological applications [1]. Phage display has been widely used in the industry due to its feasibility to select Fab fragments [2]. The Fab fragment of an immunoglobulin is a heterodimer of the N-terminal half of a heavy (H) chain and a complete light (L) chain. Because the Fab is more native-like than the single-chain Fv (scFv), which is the other commonly used recombinant antibody format for in vitro selection, the Fab fragment format makes it able to select more practical antibodies [3]. Other than phage display, cell-free translation-based methods such as ribosome display [4] and mRNA display [5] are being used for in vitro selection of antibodies due to its advantage of permitting speedier selection from larger size libraries than cell-based methods. However, these cell-free translation-based methods are limited to select scFvs due to its characteristic of linking a nascent polypeptide with its encoding mRNA on the ribosome. To overcome this limit, we have recently developed a bicistronic DNA display to select Fab fragments in a cell-free translation system [6]. Bicistronic DNA display relies on in vitro compartmentalization in water-in-oil emulsions [7], and the man-made cell-like compartments make
%U http://www.hindawi.com/journals/jna/2012/371379/