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Research

A Versatile Nanotrap for Biochemical and Functional Studies with Fluorescent Fusion Proteins^*,S

Ulrich Rothbauer, Kourosh Zolghadr, Serge Muyldermans, Aloys Schepers^¶, M. Cristina Cardoso^|| and Heinrich Leonhardt^,**

From the Munich Center for Integrated Protein Science, (CiPS^M) and Department of Biology, Ludwig Maximilians University Munich, 82152 Planegg-Martinsried, Germany, Department of Molecular and Cellular Interactions, VIB and Laboratory of Cellular and Molecular Immunology, Vrije Universiteit Brussel, 1050 Brussels, Belgium, ^¶ Departments of Gene Vectors, GSF-National Research Center for Environment and Health, 81377 Munich, Germany, and ^|| Max Delbrueck Center for Molecular Medicine, 13125 Berlin, Germany

Green fluorescent proteins (GFPs) and variants thereof are widely used to study protein localization and dynamics. We engineered a specific binder for fluorescent proteins based on a 13-kDa GFP binding fragment derived from a llama single chain antibody. This GFP-binding protein (GBP) can easily be produced in bacteria and coupled to a monovalent matrix. The GBP allows a fast and efficient (one-step) isolation of GFP fusion proteins and their interacting factors for biochemical analyses including mass spectroscopy and enzyme activity measurements. Moreover GBP is also suitable for chromatin immunoprecipitations from cells expressing fluorescent DNA-binding proteins. Most importantly, GBP can be fused with cellular proteins to ectopically recruit GFP fusion proteins allowing targeted manipulation of cellular structures and processes in living cells. Because of the high affinity capture of GFP fusion proteins in vitro and in vivo and a size in the lower nanometer range we refer to the immobilized GFP-binding protein as GFP-nanotrap. This versatile GFP-nanotrap enables a unique combination of microscopic, biochemical, and functional analyses with one and the same protein.