Protein–Protein Interactions

DOI:10.1002/anie.201201717

Protein Tango:The Toolbox to Capture Interacting Partners

Anna Rutkowska and Carsten Schultz*

cross-linkers ·dimerizers ·protein–protein interactions ·small molecules

1.Introduction

In cells,protein function is usually determined by formation of multi-protein complexes as well as the dynamics of protein–protein interactions (PPIs).Techniques to enable the discovery and investigation of PPIs on a short time scale in living cells include 1)visualization of protein localization and interactions by protein fragment complementation assays or by light microscopy through F?rster resonance energy trans-fer (FRET)measurements or fluorescence cross correlation spectroscopy (FCCS),2)manipulation of cellular protein levels (by overexpression or knockdown),and 3)immuno-precipitation of protein complexes from cell lysates.[1]More-over,protein interaction maps (interactomes)are currently produced with the help of biochemical methods performed at the proteomic scale (e.g.yeast-2-hybrid screens,protein arrays,and affinity purification techniques combined with mass spectrometry).[2]In all cases,the large set of detectable new PPIs is limited to fairly strong interactions,and the dataset requires validation and further characterization by complementary methods.

One possible solution to improve the analysis is based on the use of small molecules,that is,cross-linkers and chemical inducers of dimerization (CIDs;Figure 1),[3]to extend the

lifetime of protein complexes and to demonstrate function-ality of the PPI.Two general approaches are pursued:covalent fixation of existing PPIs through chemical cross-linkers or induction of protein interaction by CIDs.In both cases,the proteins of interest are linked in a stable,reversible or irreversible,manner.These techniques can be used to control protein activity and localization or to manipulate the oligomeric state of proteins.

Herein we highlight the available chemical dimerizers and cross-linkers and provide examples of their biological appli-cations in signal transduction,gene expression,or protein secretion.Moreover,novel strategies are discussed that may lead to improved tools and broader applications in the future.

T he evaluation of protein function in the context of the whole cell is

crucial for understanding of living systems.In this context,the iden-tification and modulation of protein–protein interactions in and outside cells is of ample importance.Several methods have been developed in the past years to detect and/or actively induce protein–protein interactions in living cells.As a result,tools are now available to manipulate intracellular events by reversible or irreversible cross-linking of proteins in a specific manner.These techniques open many new doors and enable the dissection of complicated protein networks.Herein we describe which cross-linkers and inducers of dimerization are out there and how to make use of this great

toolbox.

Figure 1.Concepts behind cross-linkers and dimerizers/chemical in-ducers of dimerization (CIDs).CIDs are applied to artificially force dimerization of any two proteins of interest by forming a stable ternary complex.In contrast,cross-linkers are designed to detect and monitor existing protein–protein interactions.They covalently bind to specific functional groups on the protein of interest.

[*]Dr.A.Rutkowska,Priv.-Doz.Dr.C.Schultz Cell Biology &Biophysics Unit

European Molecular Biology Laboratory

Meyerhofstr.1,69117Heidelberg (Germany)E-mail:schultz@embl.de

.Angewandte

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C.Schultz and A.Rutkowska

2

2012Wiley-VCH Verlag GmbH &Co.KGaA,Weinheim

Angew.Chem.Int.Ed.2012,51,2–13

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